linux-kernel - Re: [PATCH] x86/fpu: Fix potential NULL dereference in avx512

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <aH8jFcoU0C82QkNS@infradead.org>
Date: Mon, 21 Jul 2025 22:35:17 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Sohil Mehta <sohil.mehta@...el.com>,
	Fushuai Wang <wangfushuai@...du.com>, aruna.ramakrishna@...cle.com,
	aubrey.li@...el.com, bp@...en8.de, brgerst@...il.com,
	chang.seok.bae@...el.com, dave.hansen@...ux.intel.com,
	hpa@...or.com, linux-kernel@...r.kernel.org, mingo@...hat.com,
	oleg@...hat.com, peterz@...radead.org, rick.p.edgecombe@...el.com,
	seanjc@...gle.com, tglx@...utronix.de, vigbalas@....com,
	x86@...nel.org
Subject: Re: [PATCH] x86/fpu: Fix potential NULL dereference in
 avx512_status()

On Mon, Jul 21, 2025 at 07:09:52AM -0700, Dave Hansen wrote:
> On 7/18/25 16:48, Sohil Mehta wrote:
> > +       /* Do not report AVX512 usage for kernel threads */
> > +       if (!(task->flags & (PF_KTHREAD | PF_USER_WORKER)))
> > +               timestamp = READ_ONCE(x86_task_fpu(task)->avx512_timestamp);
> 
> But the original reason that folks wanted this was so they can go find
> all the AVX-512 users and cluster them together. They obviously can't do
> that today if they're oopsing their kernels.
> 
> But the real question to ask here is whether kernel threads can use
> AVX-512, and whether it's important to let userspace know which threads
> are using it.
> 
> Let's fix the oops, then circle around and figure out whether tracking
> AVX-512 use in kernel threads is needed.

The RAID6 Q-stripe calculation has a AVX512 implementation which
usually is called from workqueue context.