diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2023-02-10 10:10:57 +0000 |
|---|---|---|
| committer | Borislav Petkov (AMD) <bp@alien8.de> | 2023-05-31 13:40:57 +0200 |
| commit | 3496d1c64a0fcc9bae3ed40decc3ecd7f8ac072f (patch) | |
| tree | e2ed900906cd5a8d4939a1301fad233c48583a71 /arch/x86/include/asm/nospec-branch.h | |
| parent | df25edbac31ea87b488789d44a362063542b5967 (diff) | |
x86/nospec: Shorten RESET_CALL_DEPTH
RESET_CALL_DEPTH is a pretty fat monster and blows up UNTRAIN_RET to
20 bytes:
19: 48 c7 c0 80 00 00 00 mov $0x80,%rax
20: 48 c1 e0 38 shl $0x38,%rax
24: 65 48 89 04 25 00 00 00 00 mov %rax,%gs:0x0 29: R_X86_64_32S pcpu_hot+0x10
Shrink it by 4 bytes:
0: 31 c0 xor %eax,%eax
2: 48 0f ba e8 3f bts $0x3f,%rax
7: 65 48 89 04 25 00 00 00 00 mov %rax,%gs:0x0
Shrink RESET_CALL_DEPTH_FROM_CALL by 5 bytes by only setting %al, the
other bits are shifted out (the same could be done for RESET_CALL_DEPTH,
but the XOR+BTS sequence has less dependencies due to the zeroing).
Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230515093020.729622326@infradead.org
Diffstat (limited to 'arch/x86/include/asm/nospec-branch.h')
| -rw-r--r-- | arch/x86/include/asm/nospec-branch.h | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index edb2b0cb8efe..55388c9f7601 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -84,12 +84,12 @@ movq $-1, PER_CPU_VAR(pcpu_hot + X86_call_depth); #define RESET_CALL_DEPTH \ - mov $0x80, %rax; \ - shl $56, %rax; \ + xor %eax, %eax; \ + bts $63, %rax; \ movq %rax, PER_CPU_VAR(pcpu_hot + X86_call_depth); #define RESET_CALL_DEPTH_FROM_CALL \ - mov $0xfc, %rax; \ + movb $0xfc, %al; \ shl $56, %rax; \ movq %rax, PER_CPU_VAR(pcpu_hot + X86_call_depth); \ CALL_THUNKS_DEBUG_INC_CALLS |