Messages in this thread Patch in this message |  | | Date | Sat, 14 Jan 2023 17:17:28 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH] x86: combine memmove FSRM and ERMS alternatives |
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On Sat, Jan 14, 2023 at 11:42:13AM +0100, Borislav Petkov wrote: > Or, altenatively (pun intended), you can do what copy_user_generic() does and > move all that logic into C and inline asm. Which I'd prefer, actually, instead of > doing ugly asm hacks. Depends on how ugly it gets...
Alternatively #2, you can do the below as a minimal fix for stable along with explaining what we're doing there and why and then do the other things I suggested - if you'd like, that is - later and with no pressure.
Thx.
--- diff --git a/arch/x86/lib/memmove_64.S b/arch/x86/lib/memmove_64.S index 02661861e5dd..d6ffb4164cdb 100644 --- a/arch/x86/lib/memmove_64.S +++ b/arch/x86/lib/memmove_64.S @@ -38,10 +38,9 @@ SYM_FUNC_START(__memmove) cmp %rdi, %r8 jg 2f - /* FSRM implies ERMS => no length checks, do the copy directly */ .Lmemmove_begin_forward: ALTERNATIVE "cmp $0x20, %rdx; jb 1f", "", X86_FEATURE_FSRM - ALTERNATIVE "", "jmp .Lmemmove_erms", X86_FEATURE_ERMS + ALTERNATIVE "cmp $0x20, %rdx; jb 1f", "jmp .Lmemmove_erms", X86_FEATURE_ERMS /* * movsq instruction have many startup latency
-- Regards/Gruss, Boris.
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