linux-kernel - Re: [PATCH] x86/fpu: Allow PKRU to be (once again) written by ptrace. #forregzbot

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Date:   Mon, 21 Nov 2022 09:36:04 +0100
From:   Thorsten Leemhuis <regressions@...mhuis.info>
To:     "regressions@...ts.linux.dev" <regressions@...ts.linux.dev>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] x86/fpu: Allow PKRU to be (once again) written by ptrace.
 #forregzbot

[Note: this mail is primarily send for documentation purposes and/or for
regzbot, my Linux kernel regression tracking bot. That's why I removed
most or all folks from the list of recipients, but left any that looked
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subject, to make them easy to spot and filter out.]

On 09.11.22 11:23, Thorsten Leemhuis wrote:

> On 31.07.22 07:03, Kyle Huey wrote:
>> From: Kyle Huey <me@...ehuey.com>
>>
>> When management of the PKRU register was moved away from XSTATE, emulation
>> of PKRU's existence in XSTATE was added for APIs that read XSTATE, but not
>> for APIs that write XSTATE. This can be seen by running gdb and executing
>> `p $pkru`, `set $pkru = 42`, and `p $pkru`. On affected kernels (5.14+) the
>> write to the PKRU register (which gdb performs through ptrace) is ignored.
> 
> Seem I missed this one, but apparently it needs tracking.
> 
> #regzbot ^introduced e84ba47e313dbc
> #regzbot title x86/fpu: emulation of PKRU's existence in XSTATE missing
> for APIs that write XSTATE
> #regzbot ignore-activity
> #regzbot monitor
> https://lore.kernel.org/all/20221107063807.81774-1-khuey@kylehuey.com/

#regzbot fixed-by: 4a804c4f83