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

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Date:   Sat, 25 Apr 2020 13:09:53 +0200
From:   Jürgen Groß <jgross@...e.com>
To:     Borislav Petkov <bp@...en8.de>,
        Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Michael Matz <matz@...e.de>, Jakub Jelinek <jakub@...hat.com>,
        Sergei Trofimovich <slyfox@...too.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Kees Cook <keescook@...omium.org>,
        Martin Liška <mliska@...e.cz>,
        Frédéric Pierret (fepitre) 
        <frederic.pierret@...es-os.org>, boris.ostrovsky@...cle.com
Subject: Re: [PATCH] x86: Fix early boot crash on gcc-10, next try

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@qubes-os.org
> 
> I probably should point the folks to this thread. CCed.
> 
> Boris O, Jürgen, I'm guessing I should fix cpu_bringup_and_idle() too,
> see:
> 
> https://lkml.kernel.org/r/20200423161126.GD26021@zn.tnic
> 
> or do you prefer a separate patch?

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


Juergen