commit aa8a5e0062ac940f7659394f4817c948dc8c0667 upstream.
On some CPUs we can prevent the Meltdown vulnerability by flushing the L1-D cache on exit from kernel to user mode, and from hypervisor to guest.
This is known to be the case on at least Power7, Power8 and Power9. At this time we do not know the status of the vulnerability on other CPUs such as the 970 (Apple G5), pasemi CPUs (AmigaOne X1000) or Freescale CPUs. As more information comes to light we can enable this, or other mechanisms on those CPUs.
The vulnerability occurs when the load of an architecturally inaccessible memory region (eg. userspace load of kernel memory) is speculatively executed to the point where its result can influence the address of a subsequent speculatively executed load.
In order for that to happen, the first load must hit in the L1, because before the load is sent to the L2 the permission check is performed. Therefore if no kernel addresses hit in the L1 the vulnerability can not occur. We can ensure that is the case by flushing the L1 whenever we return to userspace. Similarly for hypervisor vs guest.
In order to flush the L1-D cache on exit, we add a section of nops at each (h)rfi location that returns to a lower privileged context, and patch that with some sequence. Newer firmwares are able to advertise to us that there is a special nop instruction that flushes the L1-D. If we do not see that advertised, we fall back to doing a displacement flush in software.
For guest kernels we support migration between some CPU versions, and different CPUs may use different flush instructions. So that we are prepared to migrate to a machine with a different flush instruction activated, we may have to patch more than one flush instruction at boot if the hypervisor tells us to.
In the end this patch is mostly the work of Nicholas Piggin and Michael Ellerman. However a cast of thousands contributed to analysis of the issue, earlier versions of the patch, back ports testing etc. Many thanks to all of them.
Signed-off-by: Nicholas Piggin npiggin@gmail.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au [Balbir - back ported to stable with changes] Signed-off-by: Balbir Singh bsingharora@gmail.com --- arch/powerpc/include/asm/exception-64s.h | 40 +++++++++++--- arch/powerpc/include/asm/feature-fixups.h | 15 ++++++ arch/powerpc/include/asm/paca.h | 10 ++++ arch/powerpc/include/asm/setup.h | 13 +++++ arch/powerpc/kernel/asm-offsets.c | 4 ++ arch/powerpc/kernel/exceptions-64s.S | 86 +++++++++++++++++++++++++++++++ arch/powerpc/kernel/setup_64.c | 79 ++++++++++++++++++++++++++++ arch/powerpc/kernel/vmlinux.lds.S | 9 ++++ arch/powerpc/lib/feature-fixups.c | 42 +++++++++++++++ 9 files changed, 290 insertions(+), 8 deletions(-)
diff --git a/arch/powerpc/include/asm/exception-64s.h b/arch/powerpc/include/asm/exception-64s.h index 6dfb6e928f81..9bddbec441b8 100644 --- a/arch/powerpc/include/asm/exception-64s.h +++ b/arch/powerpc/include/asm/exception-64s.h @@ -50,34 +50,58 @@ #define EX_PPR 88 /* SMT thread status register (priority) */ #define EX_CTR 96
-/* Macros for annotating the expected destination of (h)rfid */ +/* + * Macros for annotating the expected destination of (h)rfid + * + * The nop instructions allow us to insert one or more instructions to flush the + * L1-D cache when returning to userspace or a guest. + */ +#define RFI_FLUSH_SLOT \ + RFI_FLUSH_FIXUP_SECTION; \ + nop; \ + nop; \ + nop
#define RFI_TO_KERNEL \ rfid
#define RFI_TO_USER \ - rfid + RFI_FLUSH_SLOT; \ + rfid; \ + b rfi_flush_fallback
#define RFI_TO_USER_OR_KERNEL \ - rfid + RFI_FLUSH_SLOT; \ + rfid; \ + b rfi_flush_fallback
#define RFI_TO_GUEST \ - rfid + RFI_FLUSH_SLOT; \ + rfid; \ + b rfi_flush_fallback
#define HRFI_TO_KERNEL \ hrfid
#define HRFI_TO_USER \ - hrfid + RFI_FLUSH_SLOT; \ + hrfid; \ + b hrfi_flush_fallback
#define HRFI_TO_USER_OR_KERNEL \ - hrfid + RFI_FLUSH_SLOT; \ + hrfid; \ + b hrfi_flush_fallback
#define HRFI_TO_GUEST \ - hrfid + RFI_FLUSH_SLOT; \ + hrfid; \ + b hrfi_flush_fallback
#define HRFI_TO_UNKNOWN \ - hrfid + RFI_FLUSH_SLOT; \ + hrfid; \ + b hrfi_flush_fallback
#ifdef CONFIG_RELOCATABLE #define __EXCEPTION_RELON_PROLOG_PSERIES_1(label, h) \ diff --git a/arch/powerpc/include/asm/feature-fixups.h b/arch/powerpc/include/asm/feature-fixups.h index 9a67a38bf7b9..7068bafbb2d6 100644 --- a/arch/powerpc/include/asm/feature-fixups.h +++ b/arch/powerpc/include/asm/feature-fixups.h @@ -184,4 +184,19 @@ label##3: \ FTR_ENTRY_OFFSET label##1b-label##3b; \ .popsection;
+#define RFI_FLUSH_FIXUP_SECTION \ +951: \ + .pushsection __rfi_flush_fixup,"a"; \ + .align 2; \ +952: \ + FTR_ENTRY_OFFSET 951b-952b; \ + .popsection; + + +#ifndef __ASSEMBLY__ + +extern long __start___rfi_flush_fixup, __stop___rfi_flush_fixup; + +#endif + #endif /* __ASM_POWERPC_FEATURE_FIXUPS_H */ diff --git a/arch/powerpc/include/asm/paca.h b/arch/powerpc/include/asm/paca.h index 70bd4381f8e6..45e2aefece16 100644 --- a/arch/powerpc/include/asm/paca.h +++ b/arch/powerpc/include/asm/paca.h @@ -192,6 +192,16 @@ struct paca_struct { #endif struct kvmppc_host_state kvm_hstate; #endif +#ifdef CONFIG_PPC_BOOK3S_64 + /* + * rfi fallback flush must be in its own cacheline to prevent + * other paca data leaking into the L1d + */ + u64 exrfi[13] __aligned(0x80); + void *rfi_flush_fallback_area; + u64 l1d_flush_congruence; + u64 l1d_flush_sets; +#endif };
extern struct paca_struct *paca; diff --git a/arch/powerpc/include/asm/setup.h b/arch/powerpc/include/asm/setup.h index e9d384cbd021..7916b56f2e60 100644 --- a/arch/powerpc/include/asm/setup.h +++ b/arch/powerpc/include/asm/setup.h @@ -26,6 +26,19 @@ void initmem_init(void); void setup_panic(void); #define ARCH_PANIC_TIMEOUT 180
+void rfi_flush_enable(bool enable); + +/* These are bit flags */ +enum l1d_flush_type { + L1D_FLUSH_NONE = 0x1, + L1D_FLUSH_FALLBACK = 0x2, + L1D_FLUSH_ORI = 0x4, + L1D_FLUSH_MTTRIG = 0x8, +}; + +void __init setup_rfi_flush(enum l1d_flush_type, bool enable); +void do_rfi_flush_fixups(enum l1d_flush_type types); + #endif /* !__ASSEMBLY__ */
#endif /* _ASM_POWERPC_SETUP_H */ diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c index 40da69163d51..d92705e3a0c1 100644 --- a/arch/powerpc/kernel/asm-offsets.c +++ b/arch/powerpc/kernel/asm-offsets.c @@ -243,6 +243,10 @@ int main(void) #ifdef CONFIG_PPC_BOOK3S_64 DEFINE(PACAMCEMERGSP, offsetof(struct paca_struct, mc_emergency_sp)); DEFINE(PACA_IN_MCE, offsetof(struct paca_struct, in_mce)); + DEFINE(PACA_RFI_FLUSH_FALLBACK_AREA, offsetof(struct paca_struct, rfi_flush_fallback_area)); + DEFINE(PACA_EXRFI, offsetof(struct paca_struct, exrfi)); + DEFINE(PACA_L1D_FLUSH_CONGRUENCE, offsetof(struct paca_struct, l1d_flush_congruence)); + DEFINE(PACA_L1D_FLUSH_SETS, offsetof(struct paca_struct, l1d_flush_sets)); #endif DEFINE(PACAHWCPUID, offsetof(struct paca_struct, hw_cpu_id)); DEFINE(PACAKEXECSTATE, offsetof(struct paca_struct, kexec_state)); diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S index 2c6494351604..938a30fef031 100644 --- a/arch/powerpc/kernel/exceptions-64s.S +++ b/arch/powerpc/kernel/exceptions-64s.S @@ -1564,6 +1564,92 @@ power4_fixup_nap: blr #endif
+ .globl rfi_flush_fallback +rfi_flush_fallback: + SET_SCRATCH0(r13); + GET_PACA(r13); + std r9,PACA_EXRFI+EX_R9(r13) + std r10,PACA_EXRFI+EX_R10(r13) + std r11,PACA_EXRFI+EX_R11(r13) + std r12,PACA_EXRFI+EX_R12(r13) + std r8,PACA_EXRFI+EX_R13(r13) + mfctr r9 + ld r10,PACA_RFI_FLUSH_FALLBACK_AREA(r13) + ld r11,PACA_L1D_FLUSH_SETS(r13) + ld r12,PACA_L1D_FLUSH_CONGRUENCE(r13) + /* + * The load adresses are at staggered offsets within cachelines, + * which suits some pipelines better (on others it should not + * hurt). + */ + addi r12,r12,8 + mtctr r11 + DCBT_STOP_ALL_STREAM_IDS(r11) /* Stop prefetch streams */ + + /* order ld/st prior to dcbt stop all streams with flushing */ + sync +1: li r8,0 + .rept 8 /* 8-way set associative */ + ldx r11,r10,r8 + add r8,r8,r12 + xor r11,r11,r11 // Ensure r11 is 0 even if fallback area is not + add r8,r8,r11 // Add 0, this creates a dependency on the ldx + .endr + addi r10,r10,128 /* 128 byte cache line */ + bdnz 1b + + mtctr r9 + ld r9,PACA_EXRFI+EX_R9(r13) + ld r10,PACA_EXRFI+EX_R10(r13) + ld r11,PACA_EXRFI+EX_R11(r13) + ld r12,PACA_EXRFI+EX_R12(r13) + ld r8,PACA_EXRFI+EX_R13(r13) + GET_SCRATCH0(r13); + rfid + + .globl hrfi_flush_fallback +hrfi_flush_fallback: + SET_SCRATCH0(r13); + GET_PACA(r13); + std r9,PACA_EXRFI+EX_R9(r13) + std r10,PACA_EXRFI+EX_R10(r13) + std r11,PACA_EXRFI+EX_R11(r13) + std r12,PACA_EXRFI+EX_R12(r13) + std r8,PACA_EXRFI+EX_R13(r13) + mfctr r9 + ld r10,PACA_RFI_FLUSH_FALLBACK_AREA(r13) + ld r11,PACA_L1D_FLUSH_SETS(r13) + ld r12,PACA_L1D_FLUSH_CONGRUENCE(r13) + /* + * The load adresses are at staggered offsets within cachelines, + * which suits some pipelines better (on others it should not + * hurt). + */ + addi r12,r12,8 + mtctr r11 + DCBT_STOP_ALL_STREAM_IDS(r11) /* Stop prefetch streams */ + + /* order ld/st prior to dcbt stop all streams with flushing */ + sync +1: li r8,0 + .rept 8 /* 8-way set associative */ + ldx r11,r10,r8 + add r8,r8,r12 + xor r11,r11,r11 // Ensure r11 is 0 even if fallback area is not + add r8,r8,r11 // Add 0, this creates a dependency on the ldx + .endr + addi r10,r10,128 /* 128 byte cache line */ + bdnz 1b + + mtctr r9 + ld r9,PACA_EXRFI+EX_R9(r13) + ld r10,PACA_EXRFI+EX_R10(r13) + ld r11,PACA_EXRFI+EX_R11(r13) + ld r12,PACA_EXRFI+EX_R12(r13) + ld r8,PACA_EXRFI+EX_R13(r13) + GET_SCRATCH0(r13); + hrfid + /* * Hash table stuff */ diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c index a20823210ac0..1a3bd6a35c44 100644 --- a/arch/powerpc/kernel/setup_64.c +++ b/arch/powerpc/kernel/setup_64.c @@ -834,4 +834,83 @@ static int __init disable_hardlockup_detector(void) return 0; } early_initcall(disable_hardlockup_detector); + +#ifdef CONFIG_PPC_BOOK3S_64 +static enum l1d_flush_type enabled_flush_types; +static void *l1d_flush_fallback_area; +bool rfi_flush; + +static void do_nothing(void *unused) +{ + /* + * We don't need to do the flush explicitly, just enter+exit kernel is + * sufficient, the RFI exit handlers will do the right thing. + */ +} + +void rfi_flush_enable(bool enable) +{ + if (rfi_flush == enable) + return; + + if (enable) { + do_rfi_flush_fixups(enabled_flush_types); + on_each_cpu(do_nothing, NULL, 1); + } else + do_rfi_flush_fixups(L1D_FLUSH_NONE); + + rfi_flush = enable; +} + +static void init_fallback_flush(void) +{ + u64 l1d_size, limit; + int cpu; + + l1d_size = ppc64_caches.dsize; + limit = min(safe_stack_limit(), ppc64_rma_size); + + /* + * Align to L1d size, and size it at 2x L1d size, to catch possible + * hardware prefetch runoff. We don't have a recipe for load patterns to + * reliably avoid the prefetcher. + */ + l1d_flush_fallback_area = __va(memblock_alloc_base(l1d_size * 2, l1d_size, limit)); + memset(l1d_flush_fallback_area, 0, l1d_size * 2); + + for_each_possible_cpu(cpu) { + /* + * The fallback flush is currently coded for 8-way + * associativity. Different associativity is possible, but it + * will be treated as 8-way and may not evict the lines as + * effectively. + * + * 128 byte lines are mandatory. + */ + u64 c = l1d_size / 8; + + paca[cpu].rfi_flush_fallback_area = l1d_flush_fallback_area; + paca[cpu].l1d_flush_congruence = c; + paca[cpu].l1d_flush_sets = c / 128; + } +} + +void __init setup_rfi_flush(enum l1d_flush_type types, bool enable) +{ + if (types & L1D_FLUSH_FALLBACK) { + pr_info("rfi-flush: Using fallback displacement flush\n"); + init_fallback_flush(); + } + + if (types & L1D_FLUSH_ORI) + pr_info("rfi-flush: Using ori type flush\n"); + + if (types & L1D_FLUSH_MTTRIG) + pr_info("rfi-flush: Using mttrig type flush\n"); + + enabled_flush_types = types; + + rfi_flush_enable(enable); +} +#endif /* CONFIG_PPC_BOOK3S_64 */ #endif diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S index d41fd0af8980..072a23a17350 100644 --- a/arch/powerpc/kernel/vmlinux.lds.S +++ b/arch/powerpc/kernel/vmlinux.lds.S @@ -72,6 +72,15 @@ SECTIONS /* Read-only data */ RODATA
+#ifdef CONFIG_PPC64 + . = ALIGN(8); + __rfi_flush_fixup : AT(ADDR(__rfi_flush_fixup) - LOAD_OFFSET) { + __start___rfi_flush_fixup = .; + *(__rfi_flush_fixup) + __stop___rfi_flush_fixup = .; + } +#endif + EXCEPTION_TABLE(0)
NOTES :kernel :notes diff --git a/arch/powerpc/lib/feature-fixups.c b/arch/powerpc/lib/feature-fixups.c index 7ce3870d7ddd..a18d648d31a6 100644 --- a/arch/powerpc/lib/feature-fixups.c +++ b/arch/powerpc/lib/feature-fixups.c @@ -20,6 +20,7 @@ #include <asm/code-patching.h> #include <asm/page.h> #include <asm/sections.h> +#include <asm/setup.h>
struct fixup_entry { @@ -113,6 +114,47 @@ void do_feature_fixups(unsigned long value, void *fixup_start, void *fixup_end) } }
+#ifdef CONFIG_PPC_BOOK3S_64 +void do_rfi_flush_fixups(enum l1d_flush_type types) +{ + unsigned int instrs[3], *dest; + long *start, *end; + int i; + + start = PTRRELOC(&__start___rfi_flush_fixup), + end = PTRRELOC(&__stop___rfi_flush_fixup); + + instrs[0] = 0x60000000; /* nop */ + instrs[1] = 0x60000000; /* nop */ + instrs[2] = 0x60000000; /* nop */ + + if (types & L1D_FLUSH_FALLBACK) + /* b .+16 to fallback flush */ + instrs[0] = 0x48000010; + + i = 0; + if (types & L1D_FLUSH_ORI) { + instrs[i++] = 0x63ff0000; /* ori 31,31,0 speculation barrier */ + instrs[i++] = 0x63de0000; /* ori 30,30,0 L1d flush*/ + } + + if (types & L1D_FLUSH_MTTRIG) + instrs[i++] = 0x7c12dba6; /* mtspr TRIG2,r0 (SPR #882) */ + + for (i = 0; start < end; start++, i++) { + dest = (void *)start + *start; + + pr_devel("patching dest %lx\n", (unsigned long)dest); + + patch_instruction(dest, instrs[0]); + patch_instruction(dest + 1, instrs[1]); + patch_instruction(dest + 2, instrs[2]); + } + + printk(KERN_DEBUG "rfi-flush: patched %d locations\n", i); +} +#endif /* CONFIG_PPC_BOOK3S_64 */ + void do_lwsync_fixups(unsigned long value, void *fixup_start, void *fixup_end) { long *start, *end;