January 2018 - Linux-stable-mirror

[Linux-stable-mirror] Patch "x86/cpu/AMD: Make LFENCE a serializing instruction" has been added to the 4.14-stable tree

by gregkh＠linuxfoundation.org

This is a note to let you know that I've just added the patch titled x86/cpu/AMD: Make LFENCE a serializing instruction to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=sum… The filename of the patch is: x86-cpu-amd-make-lfence-a-serializing-instruction.patch and it can be found in the queue-4.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable(a)vger.kernel.org> know about it. >From e4d0e84e490790798691aaa0f2e598637f1867ec Mon Sep 17 00:00:00 2001 From: Tom Lendacky <thomas.lendacky(a)amd.com> Date: Mon, 8 Jan 2018 16:09:21 -0600 Subject: x86/cpu/AMD: Make LFENCE a serializing instruction From: Tom Lendacky <thomas.lendacky(a)amd.com> commit e4d0e84e490790798691aaa0f2e598637f1867ec upstream. To aid in speculation control, make LFENCE a serializing instruction since it has less overhead than MFENCE. This is done by setting bit 1 of MSR 0xc0011029 (DE_CFG). Some families that support LFENCE do not have this MSR. For these families, the LFENCE instruction is already serializing. Signed-off-by: Tom Lendacky <thomas.lendacky(a)amd.com> Signed-off-by: Thomas Gleixner <tglx(a)linutronix.de> Reviewed-by: Reviewed-by: Borislav Petkov <bp(a)suse.de> Cc: Peter Zijlstra <peterz(a)infradead.org> Cc: Tim Chen <tim.c.chen(a)linux.intel.com> Cc: Dave Hansen <dave.hansen(a)intel.com> Cc: Borislav Petkov <bp(a)alien8.de> Cc: Dan Williams <dan.j.williams(a)intel.com> Cc: Linus Torvalds <torvalds(a)linux-foundation.org> Cc: Greg Kroah-Hartman <gregkh(a)linux-foundation.org> Cc: David Woodhouse <dwmw(a)amazon.co.uk> Cc: Paul Turner <pjt(a)google.com> Link: https://lkml.kernel.org/r/20180108220921.12580.71694.stgit@tlendack-t1.amdo… Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- arch/x86/include/asm/msr-index.h | 2 ++ arch/x86/kernel/cpu/amd.c | 10 ++++++++++ 2 files changed, 12 insertions(+) --- a/arch/x86/include/asm/msr-index.h +++ b/arch/x86/include/asm/msr-index.h @@ -352,6 +352,8 @@ #define FAM10H_MMIO_CONF_BASE_MASK 0xfffffffULL #define FAM10H_MMIO_CONF_BASE_SHIFT 20 #define MSR_FAM10H_NODE_ID 0xc001100c +#define MSR_F10H_DECFG 0xc0011029 +#define MSR_F10H_DECFG_LFENCE_SERIALIZE_BIT 1 /* K8 MSRs */ #define MSR_K8_TOP_MEM1 0xc001001a --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -829,6 +829,16 @@ static void init_amd(struct cpuinfo_x86 set_cpu_cap(c, X86_FEATURE_K8); if (cpu_has(c, X86_FEATURE_XMM2)) { + /* + * A serializing LFENCE has less overhead than MFENCE, so + * use it for execution serialization. On families which + * don't have that MSR, LFENCE is already serializing. + * msr_set_bit() uses the safe accessors, too, even if the MSR + * is not present. + */ + msr_set_bit(MSR_F10H_DECFG, + MSR_F10H_DECFG_LFENCE_SERIALIZE_BIT); + /* MFENCE stops RDTSC speculation */ set_cpu_cap(c, X86_FEATURE_MFENCE_RDTSC); } Patches currently in stable-queue which might be from thomas.lendacky(a)amd.com are queue-4.14/kvm-vmx-scrub-hardware-gprs-at-vm-exit.patch queue-4.14/x86-mm-pti-remove-dead-logic-in-pti_user_pagetable_walk.patch queue-4.14/x86-cpu-amd-make-lfence-a-serializing-instruction.patch queue-4.14/x86-alternatives-fix-optimize_nops-checking.patch queue-4.14/x86-cpu-amd-use-lfence_rdtsc-in-preference-to-mfence_rdtsc.patch

6 years, 11 months

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[Linux-stable-mirror] Patch "x86/alternatives: Fix optimize_nops() checking" has been added to the 4.14-stable tree

by gregkh＠linuxfoundation.org

This is a note to let you know that I've just added the patch titled x86/alternatives: Fix optimize_nops() checking to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=sum… The filename of the patch is: x86-alternatives-fix-optimize_nops-checking.patch and it can be found in the queue-4.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable(a)vger.kernel.org> know about it. >From 612e8e9350fd19cae6900cf36ea0c6892d1a0dca Mon Sep 17 00:00:00 2001 From: Borislav Petkov <bp(a)suse.de> Date: Wed, 10 Jan 2018 12:28:16 +0100 Subject: x86/alternatives: Fix optimize_nops() checking From: Borislav Petkov <bp(a)suse.de> commit 612e8e9350fd19cae6900cf36ea0c6892d1a0dca upstream. The alternatives code checks only the first byte whether it is a NOP, but with NOPs in front of the payload and having actual instructions after it breaks the "optimized' test. Make sure to scan all bytes before deciding to optimize the NOPs in there. Reported-by: David Woodhouse <dwmw2(a)infradead.org> Signed-off-by: Borislav Petkov <bp(a)suse.de> Signed-off-by: Thomas Gleixner <tglx(a)linutronix.de> Cc: Tom Lendacky <thomas.lendacky(a)amd.com> Cc: Andi Kleen <ak(a)linux.intel.com> Cc: Tim Chen <tim.c.chen(a)linux.intel.com> Cc: Peter Zijlstra <peterz(a)infradead.org> Cc: Jiri Kosina <jikos(a)kernel.org> Cc: Dave Hansen <dave.hansen(a)intel.com> Cc: Andi Kleen <andi(a)firstfloor.org> Cc: Andrew Lutomirski <luto(a)kernel.org> Cc: Linus Torvalds <torvalds(a)linux-foundation.org> Cc: Greg Kroah-Hartman <gregkh(a)linux-foundation.org> Cc: Paul Turner <pjt(a)google.com> Link: https://lkml.kernel.org/r/20180110112815.mgciyf5acwacphkq@pd.tnic Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- arch/x86/kernel/alternative.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -344,9 +344,12 @@ done: static void __init_or_module noinline optimize_nops(struct alt_instr *a, u8 *instr) { unsigned long flags; + int i; - if (instr[0] != 0x90) - return; + for (i = 0; i < a->padlen; i++) { + if (instr[i] != 0x90) + return; + } local_irq_save(flags); add_nops(instr + (a->instrlen - a->padlen), a->padlen); Patches currently in stable-queue which might be from bp(a)suse.de are queue-4.14/x86-microcode-intel-extend-bdw-late-loading-with-a-revision-check.patch queue-4.14/x86-cpu-amd-make-lfence-a-serializing-instruction.patch queue-4.14/x86-alternatives-fix-optimize_nops-checking.patch queue-4.14/x86-cpu-amd-use-lfence_rdtsc-in-preference-to-mfence_rdtsc.patch

6 years, 11 months

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[Linux-stable-mirror] Patch "sysfs/cpu: Fix typos in vulnerability documentation" has been added to the 4.14-stable tree

by gregkh＠linuxfoundation.org

This is a note to let you know that I've just added the patch titled sysfs/cpu: Fix typos in vulnerability documentation to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=sum… The filename of the patch is: sysfs-cpu-fix-typos-in-vulnerability-documentation.patch and it can be found in the queue-4.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable(a)vger.kernel.org> know about it. >From 9ecccfaa7cb5249bd31bdceb93fcf5bedb8a24d8 Mon Sep 17 00:00:00 2001 From: David Woodhouse <dwmw(a)amazon.co.uk> Date: Tue, 9 Jan 2018 15:02:51 +0000 Subject: sysfs/cpu: Fix typos in vulnerability documentation From: David Woodhouse <dwmw(a)amazon.co.uk> commit 9ecccfaa7cb5249bd31bdceb93fcf5bedb8a24d8 upstream. Fixes: 87590ce6e ("sysfs/cpu: Add vulnerability folder") Signed-off-by: David Woodhouse <dwmw(a)amazon.co.uk> Signed-off-by: Thomas Gleixner <tglx(a)linutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- Documentation/ABI/testing/sysfs-devices-system-cpu | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -378,7 +378,7 @@ What: /sys/devices/system/cpu/vulnerabi /sys/devices/system/cpu/vulnerabilities/meltdown /sys/devices/system/cpu/vulnerabilities/spectre_v1 /sys/devices/system/cpu/vulnerabilities/spectre_v2 -Date: Januar 2018 +Date: January 2018 Contact: Linux kernel mailing list <linux-kernel(a)vger.kernel.org> Description: Information about CPU vulnerabilities @@ -388,4 +388,4 @@ Description: Information about CPU vulne "Not affected" CPU is not affected by the vulnerability "Vulnerable" CPU is affected and no mitigation in effect - "Mitigation: $M" CPU is affetcted and mitigation $M is in effect + "Mitigation: $M" CPU is affected and mitigation $M is in effect Patches currently in stable-queue which might be from dwmw(a)amazon.co.uk are queue-4.14/x86-cpufeatures-add-x86_bug_spectre_v.patch queue-4.14/x86-mm-pti-remove-dead-logic-in-pti_user_pagetable_walk.patch queue-4.14/sysfs-cpu-fix-typos-in-vulnerability-documentation.patch queue-4.14/x86-cpu-amd-make-lfence-a-serializing-instruction.patch queue-4.14/x86-cpu-implement-cpu-vulnerabilites-sysfs-functions.patch queue-4.14/x86-tboot-unbreak-tboot-with-pti-enabled.patch queue-4.14/sysfs-cpu-add-vulnerability-folder.patch queue-4.14/x86-cpu-amd-use-lfence_rdtsc-in-preference-to-mfence_rdtsc.patch

6 years, 11 months

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[Linux-stable-mirror] Patch "x86/Documentation: Add PTI description" has been added to the 4.9-stable tree

by gregkh＠linuxfoundation.org

This is a note to let you know that I've just added the patch titled x86/Documentation: Add PTI description to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=sum… The filename of the patch is: x86-documentation-add-pti-description.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable(a)vger.kernel.org> know about it. >From 01c9b17bf673b05bb401b76ec763e9730ccf1376 Mon Sep 17 00:00:00 2001 From: Dave Hansen <dave.hansen(a)linux.intel.com> Date: Fri, 5 Jan 2018 09:44:36 -0800 Subject: x86/Documentation: Add PTI description From: Dave Hansen <dave.hansen(a)linux.intel.com> commit 01c9b17bf673b05bb401b76ec763e9730ccf1376 upstream. Add some details about how PTI works, what some of the downsides are, and how to debug it when things go wrong. Also document the kernel parameter: 'pti/nopti'. Signed-off-by: Dave Hansen <dave.hansen(a)linux.intel.com> Signed-off-by: Thomas Gleixner <tglx(a)linutronix.de> Reviewed-by: Randy Dunlap <rdunlap(a)infradead.org> Reviewed-by: Kees Cook <keescook(a)chromium.org> Cc: Moritz Lipp <moritz.lipp(a)iaik.tugraz.at> Cc: Daniel Gruss <daniel.gruss(a)iaik.tugraz.at> Cc: Michael Schwarz <michael.schwarz(a)iaik.tugraz.at> Cc: Richard Fellner <richard.fellner(a)student.tugraz.at> Cc: Andy Lutomirski <luto(a)kernel.org> Cc: Linus Torvalds <torvalds(a)linux-foundation.org> Cc: Hugh Dickins <hughd(a)google.com> Cc: Andi Lutomirsky <luto(a)kernel.org> Cc: stable(a)vger.kernel.org Link: https://lkml.kernel.org/r/20180105174436.1BC6FA2B@viggo.jf.intel.com Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- Documentation/kernel-parameters.txt | 21 ++-- Documentation/x86/pti.txt | 186 ++++++++++++++++++++++++++++++++++++ 2 files changed, 200 insertions(+), 7 deletions(-) --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -2763,8 +2763,6 @@ bytes respectively. Such letter suffixes nojitter [IA-64] Disables jitter checking for ITC timers. - nopti [X86-64] Disable KAISER isolation of kernel from user. - no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page @@ -3327,11 +3325,20 @@ bytes respectively. Such letter suffixes pt. [PARIDE] See Documentation/blockdev/paride.txt. - pti= [X86_64] - Control KAISER user/kernel address space isolation: - on - enable - off - disable - auto - default setting + pti= [X86_64] Control Page Table Isolation of user and + kernel address spaces. Disabling this feature + removes hardening, but improves performance of + system calls and interrupts. + + on - unconditionally enable + off - unconditionally disable + auto - kernel detects whether your CPU model is + vulnerable to issues that PTI mitigates + + Not specifying this option is equivalent to pti=auto. + + nopti [X86_64] + Equivalent to pti=off pty.legacy_count= [KNL] Number of legacy pty's. Overwrites compiled-in --- /dev/null +++ b/Documentation/x86/pti.txt @@ -0,0 +1,186 @@ +Overview +======== + +Page Table Isolation (pti, previously known as KAISER[1]) is a +countermeasure against attacks on the shared user/kernel address +space such as the "Meltdown" approach[2]. + +To mitigate this class of attacks, we create an independent set of +page tables for use only when running userspace applications. When +the kernel is entered via syscalls, interrupts or exceptions, the +page tables are switched to the full "kernel" copy. When the system +switches back to user mode, the user copy is used again. + +The userspace page tables contain only a minimal amount of kernel +data: only what is needed to enter/exit the kernel such as the +entry/exit functions themselves and the interrupt descriptor table +(IDT). There are a few strictly unnecessary things that get mapped +such as the first C function when entering an interrupt (see +comments in pti.c). + +This approach helps to ensure that side-channel attacks leveraging +the paging structures do not function when PTI is enabled. It can be +enabled by setting CONFIG_PAGE_TABLE_ISOLATION=y at compile time. +Once enabled at compile-time, it can be disabled at boot with the +'nopti' or 'pti=' kernel parameters (see kernel-parameters.txt). + +Page Table Management +===================== + +When PTI is enabled, the kernel manages two sets of page tables. +The first set is very similar to the single set which is present in +kernels without PTI. This includes a complete mapping of userspace +that the kernel can use for things like copy_to_user(). + +Although _complete_, the user portion of the kernel page tables is +crippled by setting the NX bit in the top level. This ensures +that any missed kernel->user CR3 switch will immediately crash +userspace upon executing its first instruction. + +The userspace page tables map only the kernel data needed to enter +and exit the kernel. This data is entirely contained in the 'struct +cpu_entry_area' structure which is placed in the fixmap which gives +each CPU's copy of the area a compile-time-fixed virtual address. + +For new userspace mappings, the kernel makes the entries in its +page tables like normal. The only difference is when the kernel +makes entries in the top (PGD) level. In addition to setting the +entry in the main kernel PGD, a copy of the entry is made in the +userspace page tables' PGD. + +This sharing at the PGD level also inherently shares all the lower +layers of the page tables. This leaves a single, shared set of +userspace page tables to manage. One PTE to lock, one set of +accessed bits, dirty bits, etc... + +Overhead +======== + +Protection against side-channel attacks is important. But, +this protection comes at a cost: + +1. Increased Memory Use + a. Each process now needs an order-1 PGD instead of order-0. + (Consumes an additional 4k per process). + b. The 'cpu_entry_area' structure must be 2MB in size and 2MB + aligned so that it can be mapped by setting a single PMD + entry. This consumes nearly 2MB of RAM once the kernel + is decompressed, but no space in the kernel image itself. + +2. Runtime Cost + a. CR3 manipulation to switch between the page table copies + must be done at interrupt, syscall, and exception entry + and exit (it can be skipped when the kernel is interrupted, + though.) Moves to CR3 are on the order of a hundred + cycles, and are required at every entry and exit. + b. A "trampoline" must be used for SYSCALL entry. This + trampoline depends on a smaller set of resources than the + non-PTI SYSCALL entry code, so requires mapping fewer + things into the userspace page tables. The downside is + that stacks must be switched at entry time. + d. Global pages are disabled for all kernel structures not + mapped into both kernel and userspace page tables. This + feature of the MMU allows different processes to share TLB + entries mapping the kernel. Losing the feature means more + TLB misses after a context switch. The actual loss of + performance is very small, however, never exceeding 1%. + d. Process Context IDentifiers (PCID) is a CPU feature that + allows us to skip flushing the entire TLB when switching page + tables by setting a special bit in CR3 when the page tables + are changed. This makes switching the page tables (at context + switch, or kernel entry/exit) cheaper. But, on systems with + PCID support, the context switch code must flush both the user + and kernel entries out of the TLB. The user PCID TLB flush is + deferred until the exit to userspace, minimizing the cost. + See intel.com/sdm for the gory PCID/INVPCID details. + e. The userspace page tables must be populated for each new + process. Even without PTI, the shared kernel mappings + are created by copying top-level (PGD) entries into each + new process. But, with PTI, there are now *two* kernel + mappings: one in the kernel page tables that maps everything + and one for the entry/exit structures. At fork(), we need to + copy both. + f. In addition to the fork()-time copying, there must also + be an update to the userspace PGD any time a set_pgd() is done + on a PGD used to map userspace. This ensures that the kernel + and userspace copies always map the same userspace + memory. + g. On systems without PCID support, each CR3 write flushes + the entire TLB. That means that each syscall, interrupt + or exception flushes the TLB. + h. INVPCID is a TLB-flushing instruction which allows flushing + of TLB entries for non-current PCIDs. Some systems support + PCIDs, but do not support INVPCID. On these systems, addresses + can only be flushed from the TLB for the current PCID. When + flushing a kernel address, we need to flush all PCIDs, so a + single kernel address flush will require a TLB-flushing CR3 + write upon the next use of every PCID. + +Possible Future Work +==================== +1. We can be more careful about not actually writing to CR3 + unless its value is actually changed. +2. Allow PTI to be enabled/disabled at runtime in addition to the + boot-time switching. + +Testing +======== + +To test stability of PTI, the following test procedure is recommended, +ideally doing all of these in parallel: + +1. Set CONFIG_DEBUG_ENTRY=y +2. Run several copies of all of the tools/testing/selftests/x86/ tests + (excluding MPX and protection_keys) in a loop on multiple CPUs for + several minutes. These tests frequently uncover corner cases in the + kernel entry code. In general, old kernels might cause these tests + themselves to crash, but they should never crash the kernel. +3. Run the 'perf' tool in a mode (top or record) that generates many + frequent performance monitoring non-maskable interrupts (see "NMI" + in /proc/interrupts). This exercises the NMI entry/exit code which + is known to trigger bugs in code paths that did not expect to be + interrupted, including nested NMIs. Using "-c" boosts the rate of + NMIs, and using two -c with separate counters encourages nested NMIs + and less deterministic behavior. + + while true; do perf record -c 10000 -e instructions,cycles -a sleep 10; done + +4. Launch a KVM virtual machine. +5. Run 32-bit binaries on systems supporting the SYSCALL instruction. + This has been a lightly-tested code path and needs extra scrutiny. + +Debugging +========= + +Bugs in PTI cause a few different signatures of crashes +that are worth noting here. + + * Failures of the selftests/x86 code. Usually a bug in one of the + more obscure corners of entry_64.S + * Crashes in early boot, especially around CPU bringup. Bugs + in the trampoline code or mappings cause these. + * Crashes at the first interrupt. Caused by bugs in entry_64.S, + like screwing up a page table switch. Also caused by + incorrectly mapping the IRQ handler entry code. + * Crashes at the first NMI. The NMI code is separate from main + interrupt handlers and can have bugs that do not affect + normal interrupts. Also caused by incorrectly mapping NMI + code. NMIs that interrupt the entry code must be very + careful and can be the cause of crashes that show up when + running perf. + * Kernel crashes at the first exit to userspace. entry_64.S + bugs, or failing to map some of the exit code. + * Crashes at first interrupt that interrupts userspace. The paths + in entry_64.S that return to userspace are sometimes separate + from the ones that return to the kernel. + * Double faults: overflowing the kernel stack because of page + faults upon page faults. Caused by touching non-pti-mapped + data in the entry code, or forgetting to switch to kernel + CR3 before calling into C functions which are not pti-mapped. + * Userspace segfaults early in boot, sometimes manifesting + as mount(8) failing to mount the rootfs. These have + tended to be TLB invalidation issues. Usually invalidating + the wrong PCID, or otherwise missing an invalidation. + +1. https://gruss.cc/files/kaiser.pdf +2. https://meltdownattack.com/meltdown.pdf Patches currently in stable-queue which might be from dave.hansen(a)linux.intel.com are queue-4.9/x86-documentation-add-pti-description.patch

6 years, 11 months

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[Linux-stable-mirror] Patch "sysfs/cpu: Add vulnerability folder" has been added to the 4.9-stable tree

by gregkh＠linuxfoundation.org

This is a note to let you know that I've just added the patch titled sysfs/cpu: Add vulnerability folder to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=sum… The filename of the patch is: sysfs-cpu-add-vulnerability-folder.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable(a)vger.kernel.org> know about it. >From 87590ce6e373d1a5401f6539f0c59ef92dd924a9 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner <tglx(a)linutronix.de> Date: Sun, 7 Jan 2018 22:48:00 +0100 Subject: sysfs/cpu: Add vulnerability folder From: Thomas Gleixner <tglx(a)linutronix.de> commit 87590ce6e373d1a5401f6539f0c59ef92dd924a9 upstream. As the meltdown/spectre problem affects several CPU architectures, it makes sense to have common way to express whether a system is affected by a particular vulnerability or not. If affected the way to express the mitigation should be common as well. Create /sys/devices/system/cpu/vulnerabilities folder and files for meltdown, spectre_v1 and spectre_v2. Allow architectures to override the show function. Signed-off-by: Thomas Gleixner <tglx(a)linutronix.de> Reviewed-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk(a)oracle.com> Cc: Peter Zijlstra <peterz(a)infradead.org> Cc: Will Deacon <will.deacon(a)arm.com> Cc: Dave Hansen <dave.hansen(a)intel.com> Cc: Linus Torvalds <torvalds(a)linuxfoundation.org> Cc: Borislav Petkov <bp(a)alien8.de> Cc: David Woodhouse <dwmw(a)amazon.co.uk> Link: https://lkml.kernel.org/r/20180107214913.096657732@linutronix.de Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- Documentation/ABI/testing/sysfs-devices-system-cpu | 16 +++++++ drivers/base/Kconfig | 3 + drivers/base/cpu.c | 48 +++++++++++++++++++++ include/linux/cpu.h | 7 +++ 4 files changed, 74 insertions(+) --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -350,3 +350,19 @@ Contact: Linux ARM Kernel Mailing list < Description: AArch64 CPU registers 'identification' directory exposes the CPU ID registers for identifying model and revision of the CPU. + +What: /sys/devices/system/cpu/vulnerabilities + /sys/devices/system/cpu/vulnerabilities/meltdown + /sys/devices/system/cpu/vulnerabilities/spectre_v1 + /sys/devices/system/cpu/vulnerabilities/spectre_v2 +Date: Januar 2018 +Contact: Linux kernel mailing list <linux-kernel(a)vger.kernel.org> +Description: Information about CPU vulnerabilities + + The files are named after the code names of CPU + vulnerabilities. The output of those files reflects the + state of the CPUs in the system. Possible output values: + + "Not affected" CPU is not affected by the vulnerability + "Vulnerable" CPU is affected and no mitigation in effect + "Mitigation: $M" CPU is affetcted and mitigation $M is in effect --- a/drivers/base/Kconfig +++ b/drivers/base/Kconfig @@ -235,6 +235,9 @@ config GENERIC_CPU_DEVICES config GENERIC_CPU_AUTOPROBE bool +config GENERIC_CPU_VULNERABILITIES + bool + config SOC_BUS bool --- a/drivers/base/cpu.c +++ b/drivers/base/cpu.c @@ -499,10 +499,58 @@ static void __init cpu_dev_register_gene #endif } +#ifdef CONFIG_GENERIC_CPU_VULNERABILITIES + +ssize_t __weak cpu_show_meltdown(struct device *dev, + struct device_attribute *attr, char *buf) +{ + return sprintf(buf, "Not affected\n"); +} + +ssize_t __weak cpu_show_spectre_v1(struct device *dev, + struct device_attribute *attr, char *buf) +{ + return sprintf(buf, "Not affected\n"); +} + +ssize_t __weak cpu_show_spectre_v2(struct device *dev, + struct device_attribute *attr, char *buf) +{ + return sprintf(buf, "Not affected\n"); +} + +static DEVICE_ATTR(meltdown, 0444, cpu_show_meltdown, NULL); +static DEVICE_ATTR(spectre_v1, 0444, cpu_show_spectre_v1, NULL); +static DEVICE_ATTR(spectre_v2, 0444, cpu_show_spectre_v2, NULL); + +static struct attribute *cpu_root_vulnerabilities_attrs[] = { + &dev_attr_meltdown.attr, + &dev_attr_spectre_v1.attr, + &dev_attr_spectre_v2.attr, + NULL +}; + +static const struct attribute_group cpu_root_vulnerabilities_group = { + .name = "vulnerabilities", + .attrs = cpu_root_vulnerabilities_attrs, +}; + +static void __init cpu_register_vulnerabilities(void) +{ + if (sysfs_create_group(&cpu_subsys.dev_root->kobj, + &cpu_root_vulnerabilities_group)) + pr_err("Unable to register CPU vulnerabilities\n"); +} + +#else +static inline void cpu_register_vulnerabilities(void) { } +#endif + void __init cpu_dev_init(void) { if (subsys_system_register(&cpu_subsys, cpu_root_attr_groups)) panic("Failed to register CPU subsystem"); cpu_dev_register_generic(); + cpu_register_vulnerabilities(); } --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -44,6 +44,13 @@ extern void cpu_remove_dev_attr(struct d extern int cpu_add_dev_attr_group(struct attribute_group *attrs); extern void cpu_remove_dev_attr_group(struct attribute_group *attrs); +extern ssize_t cpu_show_meltdown(struct device *dev, + struct device_attribute *attr, char *buf); +extern ssize_t cpu_show_spectre_v1(struct device *dev, + struct device_attribute *attr, char *buf); +extern ssize_t cpu_show_spectre_v2(struct device *dev, + struct device_attribute *attr, char *buf); + extern __printf(4, 5) struct device *cpu_device_create(struct device *parent, void *drvdata, const struct attribute_group **groups, Patches currently in stable-queue which might be from tglx(a)linutronix.de are queue-4.9/x86-microcode-intel-extend-bdw-late-loading-with-a-revision-check.patch queue-4.9/x86-documentation-add-pti-description.patch queue-4.9/x86-acpi-handle-sci-interrupts-above-legacy-space-gracefully.patch queue-4.9/sysfs-cpu-add-vulnerability-folder.patch queue-4.9/x86-acpi-reduce-code-duplication-in-mp_override_legacy_irq.patch

6 years, 11 months

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[Linux-stable-mirror] Patch "x86/Documentation: Add PTI description" has been added to the 4.4-stable tree

by gregkh＠linuxfoundation.org

This is a note to let you know that I've just added the patch titled x86/Documentation: Add PTI description to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=sum… The filename of the patch is: x86-documentation-add-pti-description.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable(a)vger.kernel.org> know about it. >From 01c9b17bf673b05bb401b76ec763e9730ccf1376 Mon Sep 17 00:00:00 2001 From: Dave Hansen <dave.hansen(a)linux.intel.com> Date: Fri, 5 Jan 2018 09:44:36 -0800 Subject: x86/Documentation: Add PTI description From: Dave Hansen <dave.hansen(a)linux.intel.com> commit 01c9b17bf673b05bb401b76ec763e9730ccf1376 upstream. Add some details about how PTI works, what some of the downsides are, and how to debug it when things go wrong. Also document the kernel parameter: 'pti/nopti'. Signed-off-by: Dave Hansen <dave.hansen(a)linux.intel.com> Signed-off-by: Thomas Gleixner <tglx(a)linutronix.de> Reviewed-by: Randy Dunlap <rdunlap(a)infradead.org> Reviewed-by: Kees Cook <keescook(a)chromium.org> Cc: Moritz Lipp <moritz.lipp(a)iaik.tugraz.at> Cc: Daniel Gruss <daniel.gruss(a)iaik.tugraz.at> Cc: Michael Schwarz <michael.schwarz(a)iaik.tugraz.at> Cc: Richard Fellner <richard.fellner(a)student.tugraz.at> Cc: Andy Lutomirski <luto(a)kernel.org> Cc: Linus Torvalds <torvalds(a)linux-foundation.org> Cc: Hugh Dickins <hughd(a)google.com> Cc: Andi Lutomirsky <luto(a)kernel.org> Cc: stable(a)vger.kernel.org Link: https://lkml.kernel.org/r/20180105174436.1BC6FA2B@viggo.jf.intel.com Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- Documentation/kernel-parameters.txt | 21 ++-- Documentation/x86/pti.txt | 186 ++++++++++++++++++++++++++++++++++++ 2 files changed, 200 insertions(+), 7 deletions(-) --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -2523,8 +2523,6 @@ bytes respectively. Such letter suffixes nojitter [IA-64] Disables jitter checking for ITC timers. - nopti [X86-64] Disable KAISER isolation of kernel from user. - no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page @@ -3056,11 +3054,20 @@ bytes respectively. Such letter suffixes pt. [PARIDE] See Documentation/blockdev/paride.txt. - pti= [X86_64] - Control KAISER user/kernel address space isolation: - on - enable - off - disable - auto - default setting + pti= [X86_64] Control Page Table Isolation of user and + kernel address spaces. Disabling this feature + removes hardening, but improves performance of + system calls and interrupts. + + on - unconditionally enable + off - unconditionally disable + auto - kernel detects whether your CPU model is + vulnerable to issues that PTI mitigates + + Not specifying this option is equivalent to pti=auto. + + nopti [X86_64] + Equivalent to pti=off pty.legacy_count= [KNL] Number of legacy pty's. Overwrites compiled-in --- /dev/null +++ b/Documentation/x86/pti.txt @@ -0,0 +1,186 @@ +Overview +======== + +Page Table Isolation (pti, previously known as KAISER[1]) is a +countermeasure against attacks on the shared user/kernel address +space such as the "Meltdown" approach[2]. + +To mitigate this class of attacks, we create an independent set of +page tables for use only when running userspace applications. When +the kernel is entered via syscalls, interrupts or exceptions, the +page tables are switched to the full "kernel" copy. When the system +switches back to user mode, the user copy is used again. + +The userspace page tables contain only a minimal amount of kernel +data: only what is needed to enter/exit the kernel such as the +entry/exit functions themselves and the interrupt descriptor table +(IDT). There are a few strictly unnecessary things that get mapped +such as the first C function when entering an interrupt (see +comments in pti.c). + +This approach helps to ensure that side-channel attacks leveraging +the paging structures do not function when PTI is enabled. It can be +enabled by setting CONFIG_PAGE_TABLE_ISOLATION=y at compile time. +Once enabled at compile-time, it can be disabled at boot with the +'nopti' or 'pti=' kernel parameters (see kernel-parameters.txt). + +Page Table Management +===================== + +When PTI is enabled, the kernel manages two sets of page tables. +The first set is very similar to the single set which is present in +kernels without PTI. This includes a complete mapping of userspace +that the kernel can use for things like copy_to_user(). + +Although _complete_, the user portion of the kernel page tables is +crippled by setting the NX bit in the top level. This ensures +that any missed kernel->user CR3 switch will immediately crash +userspace upon executing its first instruction. + +The userspace page tables map only the kernel data needed to enter +and exit the kernel. This data is entirely contained in the 'struct +cpu_entry_area' structure which is placed in the fixmap which gives +each CPU's copy of the area a compile-time-fixed virtual address. + +For new userspace mappings, the kernel makes the entries in its +page tables like normal. The only difference is when the kernel +makes entries in the top (PGD) level. In addition to setting the +entry in the main kernel PGD, a copy of the entry is made in the +userspace page tables' PGD. + +This sharing at the PGD level also inherently shares all the lower +layers of the page tables. This leaves a single, shared set of +userspace page tables to manage. One PTE to lock, one set of +accessed bits, dirty bits, etc... + +Overhead +======== + +Protection against side-channel attacks is important. But, +this protection comes at a cost: + +1. Increased Memory Use + a. Each process now needs an order-1 PGD instead of order-0. + (Consumes an additional 4k per process). + b. The 'cpu_entry_area' structure must be 2MB in size and 2MB + aligned so that it can be mapped by setting a single PMD + entry. This consumes nearly 2MB of RAM once the kernel + is decompressed, but no space in the kernel image itself. + +2. Runtime Cost + a. CR3 manipulation to switch between the page table copies + must be done at interrupt, syscall, and exception entry + and exit (it can be skipped when the kernel is interrupted, + though.) Moves to CR3 are on the order of a hundred + cycles, and are required at every entry and exit. + b. A "trampoline" must be used for SYSCALL entry. This + trampoline depends on a smaller set of resources than the + non-PTI SYSCALL entry code, so requires mapping fewer + things into the userspace page tables. The downside is + that stacks must be switched at entry time. + d. Global pages are disabled for all kernel structures not + mapped into both kernel and userspace page tables. This + feature of the MMU allows different processes to share TLB + entries mapping the kernel. Losing the feature means more + TLB misses after a context switch. The actual loss of + performance is very small, however, never exceeding 1%. + d. Process Context IDentifiers (PCID) is a CPU feature that + allows us to skip flushing the entire TLB when switching page + tables by setting a special bit in CR3 when the page tables + are changed. This makes switching the page tables (at context + switch, or kernel entry/exit) cheaper. But, on systems with + PCID support, the context switch code must flush both the user + and kernel entries out of the TLB. The user PCID TLB flush is + deferred until the exit to userspace, minimizing the cost. + See intel.com/sdm for the gory PCID/INVPCID details. + e. The userspace page tables must be populated for each new + process. Even without PTI, the shared kernel mappings + are created by copying top-level (PGD) entries into each + new process. But, with PTI, there are now *two* kernel + mappings: one in the kernel page tables that maps everything + and one for the entry/exit structures. At fork(), we need to + copy both. + f. In addition to the fork()-time copying, there must also + be an update to the userspace PGD any time a set_pgd() is done + on a PGD used to map userspace. This ensures that the kernel + and userspace copies always map the same userspace + memory. + g. On systems without PCID support, each CR3 write flushes + the entire TLB. That means that each syscall, interrupt + or exception flushes the TLB. + h. INVPCID is a TLB-flushing instruction which allows flushing + of TLB entries for non-current PCIDs. Some systems support + PCIDs, but do not support INVPCID. On these systems, addresses + can only be flushed from the TLB for the current PCID. When + flushing a kernel address, we need to flush all PCIDs, so a + single kernel address flush will require a TLB-flushing CR3 + write upon the next use of every PCID. + +Possible Future Work +==================== +1. We can be more careful about not actually writing to CR3 + unless its value is actually changed. +2. Allow PTI to be enabled/disabled at runtime in addition to the + boot-time switching. + +Testing +======== + +To test stability of PTI, the following test procedure is recommended, +ideally doing all of these in parallel: + +1. Set CONFIG_DEBUG_ENTRY=y +2. Run several copies of all of the tools/testing/selftests/x86/ tests + (excluding MPX and protection_keys) in a loop on multiple CPUs for + several minutes. These tests frequently uncover corner cases in the + kernel entry code. In general, old kernels might cause these tests + themselves to crash, but they should never crash the kernel. +3. Run the 'perf' tool in a mode (top or record) that generates many + frequent performance monitoring non-maskable interrupts (see "NMI" + in /proc/interrupts). This exercises the NMI entry/exit code which + is known to trigger bugs in code paths that did not expect to be + interrupted, including nested NMIs. Using "-c" boosts the rate of + NMIs, and using two -c with separate counters encourages nested NMIs + and less deterministic behavior. + + while true; do perf record -c 10000 -e instructions,cycles -a sleep 10; done + +4. Launch a KVM virtual machine. +5. Run 32-bit binaries on systems supporting the SYSCALL instruction. + This has been a lightly-tested code path and needs extra scrutiny. + +Debugging +========= + +Bugs in PTI cause a few different signatures of crashes +that are worth noting here. + + * Failures of the selftests/x86 code. Usually a bug in one of the + more obscure corners of entry_64.S + * Crashes in early boot, especially around CPU bringup. Bugs + in the trampoline code or mappings cause these. + * Crashes at the first interrupt. Caused by bugs in entry_64.S, + like screwing up a page table switch. Also caused by + incorrectly mapping the IRQ handler entry code. + * Crashes at the first NMI. The NMI code is separate from main + interrupt handlers and can have bugs that do not affect + normal interrupts. Also caused by incorrectly mapping NMI + code. NMIs that interrupt the entry code must be very + careful and can be the cause of crashes that show up when + running perf. + * Kernel crashes at the first exit to userspace. entry_64.S + bugs, or failing to map some of the exit code. + * Crashes at first interrupt that interrupts userspace. The paths + in entry_64.S that return to userspace are sometimes separate + from the ones that return to the kernel. + * Double faults: overflowing the kernel stack because of page + faults upon page faults. Caused by touching non-pti-mapped + data in the entry code, or forgetting to switch to kernel + CR3 before calling into C functions which are not pti-mapped. + * Userspace segfaults early in boot, sometimes manifesting + as mount(8) failing to mount the rootfs. These have + tended to be TLB invalidation issues. Usually invalidating + the wrong PCID, or otherwise missing an invalidation. + +1. https://gruss.cc/files/kaiser.pdf +2. https://meltdownattack.com/meltdown.pdf Patches currently in stable-queue which might be from dave.hansen(a)linux.intel.com are queue-4.4/x86-pti-efi-broken-conversion-from-efi-to-kernel-page-table.patch queue-4.4/x86-documentation-add-pti-description.patch

6 years, 11 months

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[Linux-stable-mirror] Patch "sysfs/cpu: Add vulnerability folder" has been added to the 4.4-stable tree

by gregkh＠linuxfoundation.org

This is a note to let you know that I've just added the patch titled sysfs/cpu: Add vulnerability folder to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=sum… The filename of the patch is: sysfs-cpu-add-vulnerability-folder.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable(a)vger.kernel.org> know about it. >From 87590ce6e373d1a5401f6539f0c59ef92dd924a9 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner <tglx(a)linutronix.de> Date: Sun, 7 Jan 2018 22:48:00 +0100 Subject: sysfs/cpu: Add vulnerability folder From: Thomas Gleixner <tglx(a)linutronix.de> commit 87590ce6e373d1a5401f6539f0c59ef92dd924a9 upstream. As the meltdown/spectre problem affects several CPU architectures, it makes sense to have common way to express whether a system is affected by a particular vulnerability or not. If affected the way to express the mitigation should be common as well. Create /sys/devices/system/cpu/vulnerabilities folder and files for meltdown, spectre_v1 and spectre_v2. Allow architectures to override the show function. Signed-off-by: Thomas Gleixner <tglx(a)linutronix.de> Reviewed-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk(a)oracle.com> Cc: Peter Zijlstra <peterz(a)infradead.org> Cc: Will Deacon <will.deacon(a)arm.com> Cc: Dave Hansen <dave.hansen(a)intel.com> Cc: Linus Torvalds <torvalds(a)linuxfoundation.org> Cc: Borislav Petkov <bp(a)alien8.de> Cc: David Woodhouse <dwmw(a)amazon.co.uk> Link: https://lkml.kernel.org/r/20180107214913.096657732@linutronix.de Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- Documentation/ABI/testing/sysfs-devices-system-cpu | 16 +++++++ drivers/base/Kconfig | 3 + drivers/base/cpu.c | 48 +++++++++++++++++++++ include/linux/cpu.h | 7 +++ 4 files changed, 74 insertions(+) --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -271,3 +271,19 @@ Description: Parameters for the CPU cach - WriteBack: data is written only to the cache line and the modified cache line is written to main memory only when it is replaced + +What: /sys/devices/system/cpu/vulnerabilities + /sys/devices/system/cpu/vulnerabilities/meltdown + /sys/devices/system/cpu/vulnerabilities/spectre_v1 + /sys/devices/system/cpu/vulnerabilities/spectre_v2 +Date: Januar 2018 +Contact: Linux kernel mailing list <linux-kernel(a)vger.kernel.org> +Description: Information about CPU vulnerabilities + + The files are named after the code names of CPU + vulnerabilities. The output of those files reflects the + state of the CPUs in the system. Possible output values: + + "Not affected" CPU is not affected by the vulnerability + "Vulnerable" CPU is affected and no mitigation in effect + "Mitigation: $M" CPU is affetcted and mitigation $M is in effect --- a/drivers/base/Kconfig +++ b/drivers/base/Kconfig @@ -223,6 +223,9 @@ config GENERIC_CPU_DEVICES config GENERIC_CPU_AUTOPROBE bool +config GENERIC_CPU_VULNERABILITIES + bool + config SOC_BUS bool --- a/drivers/base/cpu.c +++ b/drivers/base/cpu.c @@ -498,10 +498,58 @@ static void __init cpu_dev_register_gene #endif } +#ifdef CONFIG_GENERIC_CPU_VULNERABILITIES + +ssize_t __weak cpu_show_meltdown(struct device *dev, + struct device_attribute *attr, char *buf) +{ + return sprintf(buf, "Not affected\n"); +} + +ssize_t __weak cpu_show_spectre_v1(struct device *dev, + struct device_attribute *attr, char *buf) +{ + return sprintf(buf, "Not affected\n"); +} + +ssize_t __weak cpu_show_spectre_v2(struct device *dev, + struct device_attribute *attr, char *buf) +{ + return sprintf(buf, "Not affected\n"); +} + +static DEVICE_ATTR(meltdown, 0444, cpu_show_meltdown, NULL); +static DEVICE_ATTR(spectre_v1, 0444, cpu_show_spectre_v1, NULL); +static DEVICE_ATTR(spectre_v2, 0444, cpu_show_spectre_v2, NULL); + +static struct attribute *cpu_root_vulnerabilities_attrs[] = { + &dev_attr_meltdown.attr, + &dev_attr_spectre_v1.attr, + &dev_attr_spectre_v2.attr, + NULL +}; + +static const struct attribute_group cpu_root_vulnerabilities_group = { + .name = "vulnerabilities", + .attrs = cpu_root_vulnerabilities_attrs, +}; + +static void __init cpu_register_vulnerabilities(void) +{ + if (sysfs_create_group(&cpu_subsys.dev_root->kobj, + &cpu_root_vulnerabilities_group)) + pr_err("Unable to register CPU vulnerabilities\n"); +} + +#else +static inline void cpu_register_vulnerabilities(void) { } +#endif + void __init cpu_dev_init(void) { if (subsys_system_register(&cpu_subsys, cpu_root_attr_groups)) panic("Failed to register CPU subsystem"); cpu_dev_register_generic(); + cpu_register_vulnerabilities(); } --- a/include/linux/cpu.h +++ b/include/linux/cpu.h @@ -40,6 +40,13 @@ extern void cpu_remove_dev_attr(struct d extern int cpu_add_dev_attr_group(struct attribute_group *attrs); extern void cpu_remove_dev_attr_group(struct attribute_group *attrs); +extern ssize_t cpu_show_meltdown(struct device *dev, + struct device_attribute *attr, char *buf); +extern ssize_t cpu_show_spectre_v1(struct device *dev, + struct device_attribute *attr, char *buf); +extern ssize_t cpu_show_spectre_v2(struct device *dev, + struct device_attribute *attr, char *buf); + extern __printf(4, 5) struct device *cpu_device_create(struct device *parent, void *drvdata, const struct attribute_group **groups, Patches currently in stable-queue which might be from tglx(a)linutronix.de are queue-4.4/x86-mm-pat-dev-mem-remove-superfluous-error-message.patch queue-4.4/x86-microcode-intel-extend-bdw-late-loading-with-a-revision-check.patch queue-4.4/locking-mutex-allow-next-waiter-lockless-wakeup.patch queue-4.4/x86-vsdo-fix-build-on-paravirt_clock-y-kvm_guest-n.patch queue-4.4/x86-pti-efi-broken-conversion-from-efi-to-kernel-page-table.patch queue-4.4/x86-documentation-add-pti-description.patch queue-4.4/x86-acpi-handle-sci-interrupts-above-legacy-space-gracefully.patch queue-4.4/futex-replace-barrier-in-unqueue_me-with-read_once.patch queue-4.4/sysfs-cpu-add-vulnerability-folder.patch queue-4.4/x86-acpi-reduce-code-duplication-in-mp_override_legacy_irq.patch

6 years, 11 months

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[Linux-stable-mirror] Patch "x86/pti: Unbreak EFI old_memmap" has been added to the 4.14-stable tree

by gregkh＠linuxfoundation.org

This is a note to let you know that I've just added the patch titled x86/pti: Unbreak EFI old_memmap to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=sum… The filename of the patch is: x86-pti-unbreak-efi-old_memmap.patch and it can be found in the queue-4.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable(a)vger.kernel.org> know about it. >From de53c3786a3ce162a1c815d0c04c766c23ec9c0a Mon Sep 17 00:00:00 2001 From: Jiri Kosina <jkosina(a)suse.cz> Date: Fri, 5 Jan 2018 22:35:41 +0100 Subject: x86/pti: Unbreak EFI old_memmap From: Jiri Kosina <jkosina(a)suse.cz> commit de53c3786a3ce162a1c815d0c04c766c23ec9c0a upstream. EFI_OLD_MEMMAP's efi_call_phys_prolog() calls set_pgd() with swapper PGD that has PAGE_USER set, which makes PTI set NX on it, and therefore EFI can't execute it's code. Fix that by forcefully clearing _PAGE_NX from the PGD (this can't be done by the pgprot API). _PAGE_NX will be automatically reintroduced in efi_call_phys_epilog(), as _set_pgd() will again notice that this is _PAGE_USER, and set _PAGE_NX on it. Tested-by: Dimitri Sivanich <sivanich(a)hpe.com> Signed-off-by: Jiri Kosina <jkosina(a)suse.cz> Signed-off-by: Ingo Molnar <mingo(a)kernel.org> Signed-off-by: Thomas Gleixner <tglx(a)linutronix.de> Acked-by: Dave Hansen <dave.hansen(a)linux.intel.com> Cc: Andrea Arcangeli <aarcange(a)redhat.com> Cc: Ard Biesheuvel <ard.biesheuvel(a)linaro.org> Cc: Linus Torvalds <torvalds(a)linux-foundation.org> Cc: Matt Fleming <matt(a)codeblueprint.co.uk> Cc: Peter Zijlstra <peterz(a)infradead.org> Cc: Thomas Gleixner <tglx(a)linutronix.de> Cc: linux-efi(a)vger.kernel.org Link: http://lkml.kernel.org/r/nycvar.YFH.7.76.1801052215460.11852@cbobk.fhfr.pm Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- arch/x86/platform/efi/efi_64.c | 2 ++ 1 file changed, 2 insertions(+) --- a/arch/x86/platform/efi/efi_64.c +++ b/arch/x86/platform/efi/efi_64.c @@ -134,7 +134,9 @@ pgd_t * __init efi_call_phys_prolog(void pud[j] = *pud_offset(p4d_k, vaddr); } } + pgd_offset_k(pgd * PGDIR_SIZE)->pgd &= ~_PAGE_NX; } + out: __flush_tlb_all(); Patches currently in stable-queue which might be from jkosina(a)suse.cz are queue-4.14/x86-pti-unbreak-efi-old_memmap.patch

6 years, 11 months

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[Linux-stable-mirror] Patch "x86/Documentation: Add PTI description" has been added to the 4.14-stable tree

by gregkh＠linuxfoundation.org

This is a note to let you know that I've just added the patch titled x86/Documentation: Add PTI description to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=sum… The filename of the patch is: x86-documentation-add-pti-description.patch and it can be found in the queue-4.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable(a)vger.kernel.org> know about it. >From 01c9b17bf673b05bb401b76ec763e9730ccf1376 Mon Sep 17 00:00:00 2001 From: Dave Hansen <dave.hansen(a)linux.intel.com> Date: Fri, 5 Jan 2018 09:44:36 -0800 Subject: x86/Documentation: Add PTI description From: Dave Hansen <dave.hansen(a)linux.intel.com> commit 01c9b17bf673b05bb401b76ec763e9730ccf1376 upstream. Add some details about how PTI works, what some of the downsides are, and how to debug it when things go wrong. Also document the kernel parameter: 'pti/nopti'. Signed-off-by: Dave Hansen <dave.hansen(a)linux.intel.com> Signed-off-by: Thomas Gleixner <tglx(a)linutronix.de> Reviewed-by: Randy Dunlap <rdunlap(a)infradead.org> Reviewed-by: Kees Cook <keescook(a)chromium.org> Cc: Moritz Lipp <moritz.lipp(a)iaik.tugraz.at> Cc: Daniel Gruss <daniel.gruss(a)iaik.tugraz.at> Cc: Michael Schwarz <michael.schwarz(a)iaik.tugraz.at> Cc: Richard Fellner <richard.fellner(a)student.tugraz.at> Cc: Andy Lutomirski <luto(a)kernel.org> Cc: Linus Torvalds <torvalds(a)linux-foundation.org> Cc: Hugh Dickins <hughd(a)google.com> Cc: Andi Lutomirsky <luto(a)kernel.org> Link: https://lkml.kernel.org/r/20180105174436.1BC6FA2B@viggo.jf.intel.com Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- Documentation/admin-guide/kernel-parameters.txt | 21 +- Documentation/x86/pti.txt | 186 ++++++++++++++++++++++++ 2 files changed, 200 insertions(+), 7 deletions(-) --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2685,8 +2685,6 @@ steal time is computed, but won't influence scheduler behaviour - nopti [X86-64] Disable kernel page table isolation - nolapic [X86-32,APIC] Do not enable or use the local APIC. nolapic_timer [X86-32,APIC] Do not use the local APIC timer. @@ -3255,11 +3253,20 @@ pt. [PARIDE] See Documentation/blockdev/paride.txt. - pti= [X86_64] - Control user/kernel address space isolation: - on - enable - off - disable - auto - default setting + pti= [X86_64] Control Page Table Isolation of user and + kernel address spaces. Disabling this feature + removes hardening, but improves performance of + system calls and interrupts. + + on - unconditionally enable + off - unconditionally disable + auto - kernel detects whether your CPU model is + vulnerable to issues that PTI mitigates + + Not specifying this option is equivalent to pti=auto. + + nopti [X86_64] + Equivalent to pti=off pty.legacy_count= [KNL] Number of legacy pty's. Overwrites compiled-in --- /dev/null +++ b/Documentation/x86/pti.txt @@ -0,0 +1,186 @@ +Overview +======== + +Page Table Isolation (pti, previously known as KAISER[1]) is a +countermeasure against attacks on the shared user/kernel address +space such as the "Meltdown" approach[2]. + +To mitigate this class of attacks, we create an independent set of +page tables for use only when running userspace applications. When +the kernel is entered via syscalls, interrupts or exceptions, the +page tables are switched to the full "kernel" copy. When the system +switches back to user mode, the user copy is used again. + +The userspace page tables contain only a minimal amount of kernel +data: only what is needed to enter/exit the kernel such as the +entry/exit functions themselves and the interrupt descriptor table +(IDT). There are a few strictly unnecessary things that get mapped +such as the first C function when entering an interrupt (see +comments in pti.c). + +This approach helps to ensure that side-channel attacks leveraging +the paging structures do not function when PTI is enabled. It can be +enabled by setting CONFIG_PAGE_TABLE_ISOLATION=y at compile time. +Once enabled at compile-time, it can be disabled at boot with the +'nopti' or 'pti=' kernel parameters (see kernel-parameters.txt). + +Page Table Management +===================== + +When PTI is enabled, the kernel manages two sets of page tables. +The first set is very similar to the single set which is present in +kernels without PTI. This includes a complete mapping of userspace +that the kernel can use for things like copy_to_user(). + +Although _complete_, the user portion of the kernel page tables is +crippled by setting the NX bit in the top level. This ensures +that any missed kernel->user CR3 switch will immediately crash +userspace upon executing its first instruction. + +The userspace page tables map only the kernel data needed to enter +and exit the kernel. This data is entirely contained in the 'struct +cpu_entry_area' structure which is placed in the fixmap which gives +each CPU's copy of the area a compile-time-fixed virtual address. + +For new userspace mappings, the kernel makes the entries in its +page tables like normal. The only difference is when the kernel +makes entries in the top (PGD) level. In addition to setting the +entry in the main kernel PGD, a copy of the entry is made in the +userspace page tables' PGD. + +This sharing at the PGD level also inherently shares all the lower +layers of the page tables. This leaves a single, shared set of +userspace page tables to manage. One PTE to lock, one set of +accessed bits, dirty bits, etc... + +Overhead +======== + +Protection against side-channel attacks is important. But, +this protection comes at a cost: + +1. Increased Memory Use + a. Each process now needs an order-1 PGD instead of order-0. + (Consumes an additional 4k per process). + b. The 'cpu_entry_area' structure must be 2MB in size and 2MB + aligned so that it can be mapped by setting a single PMD + entry. This consumes nearly 2MB of RAM once the kernel + is decompressed, but no space in the kernel image itself. + +2. Runtime Cost + a. CR3 manipulation to switch between the page table copies + must be done at interrupt, syscall, and exception entry + and exit (it can be skipped when the kernel is interrupted, + though.) Moves to CR3 are on the order of a hundred + cycles, and are required at every entry and exit. + b. A "trampoline" must be used for SYSCALL entry. This + trampoline depends on a smaller set of resources than the + non-PTI SYSCALL entry code, so requires mapping fewer + things into the userspace page tables. The downside is + that stacks must be switched at entry time. + d. Global pages are disabled for all kernel structures not + mapped into both kernel and userspace page tables. This + feature of the MMU allows different processes to share TLB + entries mapping the kernel. Losing the feature means more + TLB misses after a context switch. The actual loss of + performance is very small, however, never exceeding 1%. + d. Process Context IDentifiers (PCID) is a CPU feature that + allows us to skip flushing the entire TLB when switching page + tables by setting a special bit in CR3 when the page tables + are changed. This makes switching the page tables (at context + switch, or kernel entry/exit) cheaper. But, on systems with + PCID support, the context switch code must flush both the user + and kernel entries out of the TLB. The user PCID TLB flush is + deferred until the exit to userspace, minimizing the cost. + See intel.com/sdm for the gory PCID/INVPCID details. + e. The userspace page tables must be populated for each new + process. Even without PTI, the shared kernel mappings + are created by copying top-level (PGD) entries into each + new process. But, with PTI, there are now *two* kernel + mappings: one in the kernel page tables that maps everything + and one for the entry/exit structures. At fork(), we need to + copy both. + f. In addition to the fork()-time copying, there must also + be an update to the userspace PGD any time a set_pgd() is done + on a PGD used to map userspace. This ensures that the kernel + and userspace copies always map the same userspace + memory. + g. On systems without PCID support, each CR3 write flushes + the entire TLB. That means that each syscall, interrupt + or exception flushes the TLB. + h. INVPCID is a TLB-flushing instruction which allows flushing + of TLB entries for non-current PCIDs. Some systems support + PCIDs, but do not support INVPCID. On these systems, addresses + can only be flushed from the TLB for the current PCID. When + flushing a kernel address, we need to flush all PCIDs, so a + single kernel address flush will require a TLB-flushing CR3 + write upon the next use of every PCID. + +Possible Future Work +==================== +1. We can be more careful about not actually writing to CR3 + unless its value is actually changed. +2. Allow PTI to be enabled/disabled at runtime in addition to the + boot-time switching. + +Testing +======== + +To test stability of PTI, the following test procedure is recommended, +ideally doing all of these in parallel: + +1. Set CONFIG_DEBUG_ENTRY=y +2. Run several copies of all of the tools/testing/selftests/x86/ tests + (excluding MPX and protection_keys) in a loop on multiple CPUs for + several minutes. These tests frequently uncover corner cases in the + kernel entry code. In general, old kernels might cause these tests + themselves to crash, but they should never crash the kernel. +3. Run the 'perf' tool in a mode (top or record) that generates many + frequent performance monitoring non-maskable interrupts (see "NMI" + in /proc/interrupts). This exercises the NMI entry/exit code which + is known to trigger bugs in code paths that did not expect to be + interrupted, including nested NMIs. Using "-c" boosts the rate of + NMIs, and using two -c with separate counters encourages nested NMIs + and less deterministic behavior. + + while true; do perf record -c 10000 -e instructions,cycles -a sleep 10; done + +4. Launch a KVM virtual machine. +5. Run 32-bit binaries on systems supporting the SYSCALL instruction. + This has been a lightly-tested code path and needs extra scrutiny. + +Debugging +========= + +Bugs in PTI cause a few different signatures of crashes +that are worth noting here. + + * Failures of the selftests/x86 code. Usually a bug in one of the + more obscure corners of entry_64.S + * Crashes in early boot, especially around CPU bringup. Bugs + in the trampoline code or mappings cause these. + * Crashes at the first interrupt. Caused by bugs in entry_64.S, + like screwing up a page table switch. Also caused by + incorrectly mapping the IRQ handler entry code. + * Crashes at the first NMI. The NMI code is separate from main + interrupt handlers and can have bugs that do not affect + normal interrupts. Also caused by incorrectly mapping NMI + code. NMIs that interrupt the entry code must be very + careful and can be the cause of crashes that show up when + running perf. + * Kernel crashes at the first exit to userspace. entry_64.S + bugs, or failing to map some of the exit code. + * Crashes at first interrupt that interrupts userspace. The paths + in entry_64.S that return to userspace are sometimes separate + from the ones that return to the kernel. + * Double faults: overflowing the kernel stack because of page + faults upon page faults. Caused by touching non-pti-mapped + data in the entry code, or forgetting to switch to kernel + CR3 before calling into C functions which are not pti-mapped. + * Userspace segfaults early in boot, sometimes manifesting + as mount(8) failing to mount the rootfs. These have + tended to be TLB invalidation issues. Usually invalidating + the wrong PCID, or otherwise missing an invalidation. + +1. https://gruss.cc/files/kaiser.pdf +2. https://meltdownattack.com/meltdown.pdf Patches currently in stable-queue which might be from dave.hansen(a)linux.intel.com are queue-4.14/x86-pti-unbreak-efi-old_memmap.patch queue-4.14/x86-documentation-add-pti-description.patch

6 years, 11 months

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[Linux-stable-mirror] Patch "x86/cpufeatures: Add X86_BUG_SPECTRE_V[12]" has been added to the 4.14-stable tree

by gregkh＠linuxfoundation.org

This is a note to let you know that I've just added the patch titled x86/cpufeatures: Add X86_BUG_SPECTRE_V[12] to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=sum… The filename of the patch is: x86-cpufeatures-add-x86_bug_spectre_v.patch and it can be found in the queue-4.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable(a)vger.kernel.org> know about it. >From 99c6fa2511d8a683e61468be91b83f85452115fa Mon Sep 17 00:00:00 2001 From: David Woodhouse <dwmw(a)amazon.co.uk> Date: Sat, 6 Jan 2018 11:49:23 +0000 Subject: x86/cpufeatures: Add X86_BUG_SPECTRE_V[12] From: David Woodhouse <dwmw(a)amazon.co.uk> commit 99c6fa2511d8a683e61468be91b83f85452115fa upstream. Add the bug bits for spectre v1/2 and force them unconditionally for all cpus. Signed-off-by: David Woodhouse <dwmw(a)amazon.co.uk> Signed-off-by: Thomas Gleixner <tglx(a)linutronix.de> Cc: gnomes(a)lxorguk.ukuu.org.uk Cc: Rik van Riel <riel(a)redhat.com> Cc: Andi Kleen <ak(a)linux.intel.com> Cc: Peter Zijlstra <peterz(a)infradead.org> Cc: Linus Torvalds <torvalds(a)linux-foundation.org> Cc: Jiri Kosina <jikos(a)kernel.org> Cc: Andy Lutomirski <luto(a)amacapital.net> Cc: Dave Hansen <dave.hansen(a)intel.com> Cc: Kees Cook <keescook(a)google.com> Cc: Tim Chen <tim.c.chen(a)linux.intel.com> Cc: Greg Kroah-Hartman <gregkh(a)linux-foundation.org> Cc: Paul Turner <pjt(a)google.com> Link: https://lkml.kernel.org/r/1515239374-23361-2-git-send-email-dwmw@amazon.co.… Signed-off-by: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> --- arch/x86/include/asm/cpufeatures.h | 2 ++ arch/x86/kernel/cpu/common.c | 3 +++ 2 files changed, 5 insertions(+) --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -342,5 +342,7 @@ #define X86_BUG_MONITOR X86_BUG(12) /* IPI required to wake up remote CPU */ #define X86_BUG_AMD_E400 X86_BUG(13) /* CPU is among the affected by Erratum 400 */ #define X86_BUG_CPU_MELTDOWN X86_BUG(14) /* CPU is affected by meltdown attack and needs kernel page table isolation */ +#define X86_BUG_SPECTRE_V1 X86_BUG(15) /* CPU is affected by Spectre variant 1 attack with conditional branches */ +#define X86_BUG_SPECTRE_V2 X86_BUG(16) /* CPU is affected by Spectre variant 2 attack with indirect branches */ #endif /* _ASM_X86_CPUFEATURES_H */ --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -902,6 +902,9 @@ static void __init early_identify_cpu(st if (c->x86_vendor != X86_VENDOR_AMD) setup_force_cpu_bug(X86_BUG_CPU_MELTDOWN); + setup_force_cpu_bug(X86_BUG_SPECTRE_V1); + setup_force_cpu_bug(X86_BUG_SPECTRE_V2); + fpu__init_system(c); #ifdef CONFIG_X86_32 Patches currently in stable-queue which might be from dwmw(a)amazon.co.uk are queue-4.14/x86-cpufeatures-add-x86_bug_spectre_v.patch queue-4.14/sysfs-cpu-add-vulnerability-folder.patch

6 years, 11 months

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Linux-stable-mirror January 2018