Messages in this thread | | | Date | Tue, 9 Jan 2018 17:30:09 -0800 | From | Andi Kleen <> | Subject | Re: [PATCH] x86/retpoline: Fix NOSPEC_JMP for tip |
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On Tue, Jan 09, 2018 at 06:45:34PM -0600, Tom Lendacky wrote: > On 1/9/2018 6:40 PM, Thomas Gleixner wrote: > > On Tue, 9 Jan 2018, Linus Torvalds wrote: > > > >> On Tue, Jan 9, 2018 at 4:31 PM, Andi Kleen <andi@firstfloor.org> wrote: > >>> > >>> The following patch fixes it for me. Something doesn't > >>> seem to work with ALTERNATIVE_2. It adds only a few bytes > >>> more code, so seems acceptable. > >> > >> Ugh. It's kind of stupid, though. > >> > >> Why is the code sequence not simply: > >> > >> ALTERNATIVE "", "lfence", X86_FEATURE_RETPOLINE_AMD > >> ALTERNATIVE __stringify(jmp *\reg), __stringify(RETPOLINE_JMP \reg), > >> X86_FEATURE_RETPOLINE > >> > >> ie make that X86_FEATURE_RETPOLINE_AMD _only_ emit the "lfence", and > >> simply fall through to what will be the "jmp *\reg" of the > >> non-RETPOLINE version. > >> > >> Then just make sure X86_FEATURE_RETPOLINE_AMD disables X86_FEATURE_RETPOLINE. > > I think there are areas that rely on X86_FEATURE_RETPOLINE being set > even if X86_FEATURE_RETPOLINE_AMD is set. For example, line 261 in > arch/x86/entry/entry_32.S is only checking for X86_FEATURE_RETPOLINE.
I audited the difference places. They all seem ok.
I assume you don't need FILL_RETURN_BUFFER on AMD. If not let me know and we can add a X86_FEATURE_RETPOLINE_COMMON
-Andi
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