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

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Date:   Thu, 3 Jun 2021 07:16:42 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        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>,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [patch 1/8] selftests/x86: Test signal frame XSTATE header
 corruption handling

On 6/2/21 8:15 AM, Thomas Gleixner wrote:
> 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...
> 

Yes. I will add to newcomer task list.

thanks,
-- Shuah