linux-kernel - Re: [patch 1/8] selftests/x86: Test signal frame XSTATE header corruption handling

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Date:   Wed, 02 Jun 2021 16:15:11 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Borislav Petkov <bp@...en8.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Shuah Khan <shuah@...nel.org>
Subject: Re: [patch 1/8] selftests/x86: Test signal frame XSTATE header corruption handling

On Wed, Jun 02 2021 at 14:38, Borislav Petkov wrote:
> On Wed, Jun 02, 2021 at 11:55:44AM +0200, Thomas Gleixner wrote:
>> From: Andy Lutomirski <luto@...nel.org>
>> 
>> This is very heavily based on some code from Thomas Gleixner.  On a system
>> without XSAVES, it triggers the WARN_ON():
>> 
>>     Bad FPU state detected at copy_kernel_to_fpregs+0x2f/0x40, reinitializing FPU registers.
>
> That triggers
>
> [  149.497274] corrupt_xstate_[1627] bad frame in rt_sigreturn frame:00000000dad08ab1 ip:7f031449ffe1 sp:7ffd0c5c59f0 orax:ffffffffffffffff in libpthread-2.31.so[7f0314493000+10000]
>
> on an AMD laptop here.

Yes, that's the ratelimited printk in the signal code.

>> +static inline void __cpuid(unsigned int *eax, unsigned int *ebx,
>> +			   unsigned int *ecx, unsigned int *edx)
>> +{
>> +	asm volatile(
>> +		"cpuid;"
>> +		: "=a" (*eax),
>> +		  "=b" (*ebx),
>> +		  "=c" (*ecx),
>> +		  "=d" (*edx)
>> +		: "0" (*eax), "2" (*ecx));
>> +}
>> +
>> +static inline int xsave_enabled(void)
>> +{
>> +	unsigned int eax, ebx, ecx, edx;
>> +
>> +	eax = 0x1;
>> +	ecx = 0x0;
>> +	__cpuid(&eax, &ebx, &ecx, &edx);
>> +
>> +	/* Is CR4.OSXSAVE enabled ? */
>> +	return ecx & (1U << 27);
>> +}
>
> One fine day someone should sit down and unify all those auxillary
> functions used in the selftests into a lib...

Yes please. Shuah, that would be a great newcomer task...

>> +
>> +int main()
>
> ERROR: Bad function definition - int main() should probably be int main(void)

Bah, I thought I had fixed that.