The following commit has been merged into the x86/alternatives branch of tip: Commit-ID: df25edbac31ea87b488789d44a362063542b5967 Gitweb: https://git.kernel.org/tip/df25edbac31ea87b488789d44a362063542b5967 Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx> AuthorDate: Mon, 15 May 2023 11:28:05 +02:00 Committer: Borislav Petkov (AMD) <bp@xxxxxxxxx> CommitterDate: Wed, 31 May 2023 10:21:21 +02:00 x86/alternatives: Add longer 64-bit NOPs By adding support for longer NOPs there are a few more alternatives that can turn into a single instruction. Add up to NOP11, the same limit where GNU as .nops also stops generating longer nops. This is because a number of uarchs have severe decode penalties for more than 3 prefixes. [ bp: Sync up with the version in tools/ while at it. ] Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx> Link: https://lore.kernel.org/r/20230515093020.661756940@xxxxxxxxxxxxx --- arch/x86/include/asm/nops.h | 16 ++++++++++++++-- arch/x86/kernel/alternative.c | 10 ++++++++++ tools/arch/x86/include/asm/nops.h | 16 ++++++++++++++-- 3 files changed, 38 insertions(+), 4 deletions(-) diff --git a/arch/x86/include/asm/nops.h b/arch/x86/include/asm/nops.h index c5573ea..1c1b755 100644 --- a/arch/x86/include/asm/nops.h +++ b/arch/x86/include/asm/nops.h @@ -34,6 +34,8 @@ #define BYTES_NOP7 0x8d,0xb4,0x26,0x00,0x00,0x00,0x00 #define BYTES_NOP8 0x3e,BYTES_NOP7 +#define ASM_NOP_MAX 8 + #else /* @@ -47,6 +49,9 @@ * 6: osp nopl 0x00(%eax,%eax,1) * 7: nopl 0x00000000(%eax) * 8: nopl 0x00000000(%eax,%eax,1) + * 9: cs nopl 0x00000000(%eax,%eax,1) + * 10: osp cs nopl 0x00000000(%eax,%eax,1) + * 11: osp osp cs nopl 0x00000000(%eax,%eax,1) */ #define BYTES_NOP1 0x90 #define BYTES_NOP2 0x66,BYTES_NOP1 @@ -56,6 +61,15 @@ #define BYTES_NOP6 0x66,BYTES_NOP5 #define BYTES_NOP7 0x0f,0x1f,0x80,0x00,0x00,0x00,0x00 #define BYTES_NOP8 0x0f,0x1f,0x84,0x00,0x00,0x00,0x00,0x00 +#define BYTES_NOP9 0x2e,BYTES_NOP8 +#define BYTES_NOP10 0x66,BYTES_NOP9 +#define BYTES_NOP11 0x66,BYTES_NOP10 + +#define ASM_NOP9 _ASM_BYTES(BYTES_NOP9) +#define ASM_NOP10 _ASM_BYTES(BYTES_NOP10) +#define ASM_NOP11 _ASM_BYTES(BYTES_NOP11) + +#define ASM_NOP_MAX 11 #endif /* CONFIG_64BIT */ @@ -68,8 +82,6 @@ #define ASM_NOP7 _ASM_BYTES(BYTES_NOP7) #define ASM_NOP8 _ASM_BYTES(BYTES_NOP8) -#define ASM_NOP_MAX 8 - #ifndef __ASSEMBLY__ extern const unsigned char * const x86_nops[]; #endif diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 93aa95a..0747d29 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -98,6 +98,11 @@ static const unsigned char x86nops[] = BYTES_NOP6, BYTES_NOP7, BYTES_NOP8, +#ifdef CONFIG_64BIT + BYTES_NOP9, + BYTES_NOP10, + BYTES_NOP11, +#endif }; const unsigned char * const x86_nops[ASM_NOP_MAX+1] = @@ -111,6 +116,11 @@ const unsigned char * const x86_nops[ASM_NOP_MAX+1] = x86nops + 1 + 2 + 3 + 4 + 5, x86nops + 1 + 2 + 3 + 4 + 5 + 6, x86nops + 1 + 2 + 3 + 4 + 5 + 6 + 7, +#ifdef CONFIG_64BIT + x86nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8, + x86nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9, + x86nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10, +#endif }; /* diff --git a/tools/arch/x86/include/asm/nops.h b/tools/arch/x86/include/asm/nops.h index c5573ea..1c1b755 100644 --- a/tools/arch/x86/include/asm/nops.h +++ b/tools/arch/x86/include/asm/nops.h @@ -34,6 +34,8 @@ #define BYTES_NOP7 0x8d,0xb4,0x26,0x00,0x00,0x00,0x00 #define BYTES_NOP8 0x3e,BYTES_NOP7 +#define ASM_NOP_MAX 8 + #else /* @@ -47,6 +49,9 @@ * 6: osp nopl 0x00(%eax,%eax,1) * 7: nopl 0x00000000(%eax) * 8: nopl 0x00000000(%eax,%eax,1) + * 9: cs nopl 0x00000000(%eax,%eax,1) + * 10: osp cs nopl 0x00000000(%eax,%eax,1) + * 11: osp osp cs nopl 0x00000000(%eax,%eax,1) */ #define BYTES_NOP1 0x90 #define BYTES_NOP2 0x66,BYTES_NOP1 @@ -56,6 +61,15 @@ #define BYTES_NOP6 0x66,BYTES_NOP5 #define BYTES_NOP7 0x0f,0x1f,0x80,0x00,0x00,0x00,0x00 #define BYTES_NOP8 0x0f,0x1f,0x84,0x00,0x00,0x00,0x00,0x00 +#define BYTES_NOP9 0x2e,BYTES_NOP8 +#define BYTES_NOP10 0x66,BYTES_NOP9 +#define BYTES_NOP11 0x66,BYTES_NOP10 + +#define ASM_NOP9 _ASM_BYTES(BYTES_NOP9) +#define ASM_NOP10 _ASM_BYTES(BYTES_NOP10) +#define ASM_NOP11 _ASM_BYTES(BYTES_NOP11) + +#define ASM_NOP_MAX 11 #endif /* CONFIG_64BIT */ @@ -68,8 +82,6 @@ #define ASM_NOP7 _ASM_BYTES(BYTES_NOP7) #define ASM_NOP8 _ASM_BYTES(BYTES_NOP8) -#define ASM_NOP_MAX 8 - #ifndef __ASSEMBLY__ extern const unsigned char * const x86_nops[]; #endif
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