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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <b3dbca94-8603-44ea-b778-97483fbbba94@intel.com>
Date: Mon, 21 Jul 2025 07:09:52 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Sohil Mehta <sohil.mehta@...el.com>, Fushuai Wang <wangfushuai@...du.com>
Cc: 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 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.