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Subject: Re: [PATCH] x86: Fix early boot crash on gcc-10, next try
To:     Borislav Petkov <bp@alien8.de>,
        Arvind Sankar <nivedita@alum.mit.edu>
Cc:     Nick Desaulniers <ndesaulniers@google.com>,
        Michael Matz <matz@suse.de>, Jakub Jelinek <jakub@redhat.com>,
        Sergei Trofimovich <slyfox@gentoo.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>, x86@kernel.org,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Kees Cook <keescook@chromium.org>,
        =?UTF-8?Q?Martin_Li=c5=a1ka?= <mliska@suse.cz>,
        =?UTF-8?Q?Fr=c3=a9d=c3=a9ric_Pierret_=28fepitre=29?= 
        <frederic.pierret@qubes-os.org>, boris.ostrovsky@oracle.com
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 <20200423125300.GC26021@zn.tnic> <20200423161126.GD26021@zn.tnic>
 <20200425014657.GA2191784@rani.riverdale.lan>
 <20200425085759.GA24294@zn.tnic>
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Date:   Sat, 25 Apr 2020 13:09:53 +0200
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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