This is a note to let you know that I've just added the patch titled

x86/pti: Switch to kernel CR3 at early in entry_SYSCALL_compat()

to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: x86-pti-switch-to-kernel-cr3-at-early-in-entry_syscall_compat.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@vger.kernel.org know about it.

From d7732ba55c4b6a2da339bb12589c515830cfac2c Mon Sep 17 00:00:00 2001

From: Thomas Gleixner tglx@linutronix.de Date: Wed, 3 Jan 2018 19:52:04 +0100 Subject: x86/pti: Switch to kernel CR3 at early in entry_SYSCALL_compat()

From: Thomas Gleixner tglx@linutronix.de

commit d7732ba55c4b6a2da339bb12589c515830cfac2c upstream.

The preparation for PTI which added CR3 switching to the entry code misplaced the CR3 switch in entry_SYSCALL_compat().

With PTI enabled the entry code tries to access a per cpu variable after switching to kernel GS. This fails because that variable is not mapped to user space. This results in a double fault and in the worst case a kernel crash.

Move the switch ahead of the access and clobber RSP which has been saved already.

Fixes: 8a09317b895f ("x86/mm/pti: Prepare the x86/entry assembly code for entry/exit CR3 switching") Reported-by: Lars Wendler wendler.lars@web.de Reported-by: Laura Abbott labbott@redhat.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: Borislav Betkov bp@alien8.de Cc: Andy Lutomirski luto@kernel.org, Cc: Dave Hansen dave.hansen@linux.intel.com, Cc: Peter Zijlstra peterz@infradead.org, Cc: Greg KH gregkh@linuxfoundation.org, , Cc: Boris Ostrovsky boris.ostrovsky@oracle.com, Cc: Juergen Gross jgross@suse.com Link: https://lkml.kernel.org/r/alpine.DEB.2.20.1801031949200.1957@nanos Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- arch/x86/entry/entry_64_compat.S | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-)

--- a/arch/x86/entry/entry_64_compat.S +++ b/arch/x86/entry/entry_64_compat.S @@ -190,8 +190,13 @@ ENTRY(entry_SYSCALL_compat) /* Interrupts are off on entry. */ swapgs

- /* Stash user ESP and switch to the kernel stack. */ + /* Stash user ESP */ movl %esp, %r8d + + /* Use %rsp as scratch reg. User ESP is stashed in r8 */ + SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp + + /* Switch to the kernel stack */ movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp

/* Construct struct pt_regs on stack */ @@ -220,12 +225,6 @@ GLOBAL(entry_SYSCALL_compat_after_hwfram pushq $0 /* pt_regs->r15 = 0 */

/* - * We just saved %rdi so it is safe to clobber. It is not - * preserved during the C calls inside TRACE_IRQS_OFF anyway. - */ - SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi - - /* * User mode is traced as though IRQs are on, and SYSENTER * turned them off. */

Patches currently in stable-queue which might be from tglx@linutronix.de are

queue-4.14/x86-pti-switch-to-kernel-cr3-at-early-in-entry_syscall_compat.patch queue-4.14/x86-dumpstack-print-registers-for-first-stack-frame.patch queue-4.14/x86-process-define-cpu_tss_rw-in-same-section-as-declaration.patch queue-4.14/x86-pti-make-sure-the-user-kernel-ptes-match.patch queue-4.14/x86-cpu-x86-pti-do-not-enable-pti-on-amd-processors.patch queue-4.14/x86-dumpstack-fix-partial-register-dumps.patch