Messages in this thread | | | From | Nick Desaulniers <> | Date | Wed, 22 Apr 2020 11:55:50 -0700 | Subject | Re: [PATCH v2] x86: fix early boot crash on gcc-10 |
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On Wed, Apr 22, 2020 at 3:23 AM Borislav Petkov <bp@alien8.de> wrote: > > Ok, > > let's try the simple and clean fix first. Nick, would that work on LLVM > too? > > And I hope this will remain working and the compiler won't jump over an > inline asm and go nuts. > > Thx. > > --- > diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c > index 3b9bf8c7e29d..06d2e16bedbb 100644 > --- a/arch/x86/kernel/smpboot.c > +++ b/arch/x86/kernel/smpboot.c > @@ -266,6 +266,13 @@ static void notrace start_secondary(void *unused) > > wmb(); > cpu_startup_entry(CPUHP_AP_ONLINE_IDLE); > + > + /* > + * Prevent tail call to cpu_startup_entry() because the stack protector > + * guard has been changed in the middle of this function and must not be > + * checked before tail calling another function.
Can you add by whom? It's not clear to me which function call in start_secondary modifies the stack protector guard.
Another question. Do we not want a stack protector at all in this function? I'm not super familiar with how they work; do we not want them at all, or simply not to check the guard?
But if we're not going to check it, I think __attribute__((no_stack_protector)) applied to start_secondary might be a more precise fix. Though the empty asm statement may be the most portable at this time, and with a well specified comment, I can live with it.
> + */ > + asm (""); > } > > /** > > -- > Regards/Gruss, > Boris. > > https://people.kernel.org/tglx/notes-about-netiquette
-- Thanks, ~Nick Desaulniers
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