Re: [PATCH] x86: Fix early boot crash on gcc-10, next try

[JÃrgen GroÃ]

On 25.04.20 10:57, Borislav Petkov wrote:
> On Fri, Apr 24, 2020 at 09:46:57PM -0400, Arvind Sankar wrote:
> > The comment above boot_init_stack_canary's definition should be updated
> > to note that it needs to be called from a function that, in addition to
> > not returning, either has stackprotector disabled or avoids ending in a
> > tail call.
>
> How's that?
>
> diff --git a/arch/x86/include/asm/stackprotector.h b/arch/x86/include/asm/stackprotector.h
> index 91e29b6a86a5..237a54f60d6b 100644
> --- a/arch/x86/include/asm/stackprotector.h
> +++ b/arch/x86/include/asm/stackprotector.h
> @@ -55,8 +55,12 @@
>   /*
>    * Initialize the stackprotector canary value.
>    *
> - * NOTE: this must only be called from functions that never return,
> - * and it must always be inlined.
> + * NOTE: this must only be called from functions that never return, it must
> + * always be inlined and it should be called from a compilation unit for
> + * which stack protector is disabled.
> + *
> + * Alternatively, the caller should not end with a function call which gets
> + * tail-call optimized as that would lead to checking a modified canary value.
>    */
>   static __always_inline void boot_init_stack_canary(void)
>   {
>
> > There are also other calls that likely need to be fixed as well -- in
> > init/main.c, arch/x86/xen/smp_pv.c, and there is a powerpc version of
> > start_secondary in arch/powerpc/kernel/smp.c which may also be affected.
>
> Yes, there was an attempt to fix former:
>
> https://lkml.kernel.org/r/20200413123535.10884-1-frederic.pierret@xxxxxxxxxxxx
>
> I probably should point the folks to this thread. CCed.
>
> Boris O, JÃrgen, I'm guessing I should fix cpu_bringup_and_idle() too,
> see:
>
> https://lkml.kernel.org/r/20200423161126.GD26021@xxxxxxx
>
> or do you prefer a separate patch?

I'm fine with you including it in your patch.


Juergen