Messages in this thread | | | Date | Tue, 7 Apr 2020 08:27:45 -0500 | From | Josh Poimboeuf <> | Subject | Re: [PATCH V2 6/9] x86/speculation: Change __FILL_RETURN_BUFFER to work with objtool |
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On Tue, Apr 07, 2020 at 09:31:39AM +0200, Alexandre Chartre wrote: > Change __FILL_RETURN_BUFFER so that the stack state is deterministically > defined for each iteration and that objtool can have an accurate view > of the stack. > > Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com> > --- > arch/x86/include/asm/nospec-branch.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h > index 5c24a7b35166..9a946fd5e824 100644 > --- a/arch/x86/include/asm/nospec-branch.h > +++ b/arch/x86/include/asm/nospec-branch.h > @@ -60,8 +60,8 @@ > jmp 775b; \ > 774: \ > dec reg; \ > - jnz 771b; \ > - add $(BITS_PER_LONG/8) * nr, sp; > + add $(BITS_PER_LONG/8) * 2, sp; \ > + jnz 771b; > > #ifdef __ASSEMBLY__
This still isn't a complete fix because the macro is used in an alternative. So in the !X86_FEATURE_RSB_CTXSW case, this code isn't patched in and the ORC data which refers to it is wrong.
As I said before I think the easiest fix would be to convert RSB and retpolines to use static branches instead of alternatives.
-- Josh
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