linux-kernel - Re: [PATCH] x86/bhi: BHI mitigation can trigger warning in #DB handler

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Date: Thu, 23 May 2024 16:52:02 +0200
From: Alexandre Chartre <alexandre.chartre@...cle.com>
To: Dave Hansen <dave.hansen@...el.com>, x86@...nel.org, kvm@...r.kernel.org
Cc: alexandre.chartre@...cle.com, linux-kernel@...r.kernel.org,
        daniel.sneddon@...ux.intel.com, pawan.kumar.gupta@...ux.intel.com,
        tglx@...utronix.de, konrad.wilk@...cle.com, peterz@...radead.org,
        gregkh@...uxfoundation.org, seanjc@...gle.com,
        andrew.cooper3@...rix.com, dave.hansen@...ux.intel.com,
        nik.borisov@...e.com, kpsingh@...nel.org, longman@...hat.com,
        bp@...en8.de, pbonzini@...hat.com
Subject: Re: [PATCH] x86/bhi: BHI mitigation can trigger warning in #DB
 handler


On 5/23/24 16:28, Dave Hansen wrote:
> On 5/23/24 05:33, Alexandre Chartre wrote:
>> The problem can be reproduced with the following sequence:
>>
>>   $ cat sysenter_step.c
>>   int main()
>>   { asm("pushf; pop %ax; bts $8,%ax; push %ax; popf; sysenter"); }
>>
>>   $ gcc -o sysenter_step sysenter_step.c
>>
>>   $ ./sysenter_step
>>   Segmentation fault (core dumped)
>>
>> The program is expected to crash, and the #DB handler will issue a warning.
> 
> Should we wrap up this gem and put it with the other entry selftests?

It looks like tools/testing/selftests/x86/single_step_syscall.c tests
sysenter with TF set but it doesn't check if the kernel issues any
warning.

alex.