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

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Date: Thu, 23 May 2024 18:53:34 +0100
From: Andrew Cooper <andrew.cooper3@...rix.com>
To: Alexandre Chartre <alexandre.chartre@...cle.com>,
 Dave Hansen <dave.hansen@...el.com>, x86@...nel.org, kvm@...r.kernel.org
Cc: 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, 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 23/05/2024 6:03 pm, Alexandre Chartre wrote:
>
> On 5/23/24 17:36, Dave Hansen wrote:
>> On 5/23/24 07:52, Alexandre Chartre wrote:
>>>> 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.
>>
>> Does it actually trip the warning though? I'm a bit surprised that
>> nobody reported it if so.
>
> single_step_syscall does trigger the warning:
>
> $ ./single_step_syscall
> [RUN]    Set TF and check nop
> [OK]    Survived with TF set and 26 traps
> [RUN]    Set TF and check syscall-less opportunistic sysret
> [OK]    Survived with TF set and 30 traps
> [RUN]    Set TF and check a fast syscall
> [OK]    Survived with TF set and 40 traps
> [RUN]    Fast syscall with TF cleared
> [OK]    Nothing unexpected happened
> [RUN]    Set TF and check SYSENTER
>     Got SIGSEGV with RIP=ed7fe579, TF=256
> [RUN]    Fast syscall with TF cleared
> [OK]    Nothing unexpected happened

:-/

What about the exit code?

I find the absence of a [FAIL] concerning...

~Andrew