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SubjectRe: [PATCH] x86/speculation: Use AMD specific retpoline for inline asm on AMD
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On 2018/9/18 17:50, Peter Zijlstra wrote:
> On Mon, Sep 17, 2018 at 10:17:30PM -0700, Zhenzhong Duan wrote:
>> Lfence is preferred than general retpoline on AMD, add this option
>> in C / inline asm just as the ASM code does.
>>
>> For x86_64, it still help to have minimal retpoline for kernel even
>> if gcc doesn't support it, change the inline asm for x86 so that it
>> could also be used by x86_64.
>> Add ANNOTATE_NOSPEC_ALTERNATIVE for i386 to avoid below warning:
>> "warning: objtool: .altinstr_replacement+0x10: unsupported
>> intra-function call"
>> "warning: objtool: If this is a retpoline, please patch it
>> in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE."
>
> This Changelog is almost unreadable, please rewrite.
Sorry, I'll rewrite it.

>
> Reverse engineering the patch you add RETPOLINE_AMD support to the
> inline-asm CALL_NOSPEC so that they match the asm CALL_NOSPEC.
>
>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
>> ---
>> arch/x86/include/asm/nospec-branch.h | 23 ++++++++++++++++-------
>> 1 files changed, 16 insertions(+), 7 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
>> index fd2a8c1..2d49eab 100644
>> --- a/arch/x86/include/asm/nospec-branch.h
>> +++ b/arch/x86/include/asm/nospec-branch.h
>> @@ -170,21 +170,26 @@
>> */
>> # define CALL_NOSPEC \
>> ANNOTATE_NOSPEC_ALTERNATIVE \
>> - ALTERNATIVE( \
>> + ALTERNATIVE_2( \
>> ANNOTATE_RETPOLINE_SAFE \
>> "call *%[thunk_target]\n", \
>> "call __x86_indirect_thunk_%V[thunk_target]\n", \
>> - X86_FEATURE_RETPOLINE)
>> + X86_FEATURE_RETPOLINE, \
>> + "lfence;\n" \
>> + ANNOTATE_RETPOLINE_SAFE \
>> + "call *%[thunk_target]\n", \
>> + X86_FEATURE_RETPOLINE_AMD)
>> # define THUNK_TARGET(addr) [thunk_target] "r" (addr)
>
> That's OK.
>
>>
>> -#elif defined(CONFIG_X86_32) && defined(CONFIG_RETPOLINE)
>> +#elif defined(CONFIG_RETPOLINE)
>
> This doesn't make any sense..
This change is used for x86_64 to have minimal Retpoline support when
CONFIG_RETPOLINE is defined but RETPOLINE isn't defined, or I missed
something?

>
>> /*
>> * For i386 we use the original ret-equivalent retpoline, because
>> * otherwise we'll run out of registers. We don't care about CET
>> * here, anyway.
>> */
>> # define CALL_NOSPEC \
>> - ALTERNATIVE( \
>> + ANNOTATE_NOSPEC_ALTERNATIVE \
>> + ALTERNATIVE_2( \
>> ANNOTATE_RETPOLINE_SAFE \
>> "call *%[thunk_target]\n", \
>> " jmp 904f;\n" \
>> @@ -194,12 +199,16 @@
>> " lfence;\n" \
>> " jmp 902b;\n" \
>> " .align 16\n" \
>> - "903: addl $4, %%esp;\n" \
>> - " pushl %[thunk_target];\n" \
>> + "903: add $4, %%" _ASM_SP ";\n" \
>> + " push %[thunk_target];\n" \
>
> Yeah, don't do that.
This is the change for above reason.

Thanks
Zhenzhong

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