Messages in this thread |  | | Date | Sat, 14 Jan 2023 21:49:01 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH] x86: combine memmove FSRM and ERMS alternatives |
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On Sat, Jan 14, 2023 at 05:17:28PM +0100, Borislav Petkov wrote: > 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
Forget what I said - now that I think of it this is bull.
The more and more I think about it, the more I like the copy_user_generic() idea but lemme see how ugly it gets...
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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