Description
In the Linux kernel, the following vulnerability has been resolved: x86/fpu: Fix NULL dereference in avx512_status() Problem ------- With CONFIG_X86_DEBUG_FPU enabled, reading /proc/[kthread]/arch_status causes a warning and a NULL pointer dereference. This is because the AVX-512 timestamp code uses x86_task_fpu() but doesn't check it for NULL. CONFIG_X86_DEBUG_FPU addles that function for kernel threads (PF_KTHREAD specifically), making it return NULL. The point of the warning was to ensure that kernel threads only access task->fpu after going through kernel_fpu_begin()/_end(). Note: all kernel tasks exposed in /proc have a valid task->fpu. Solution -------- One option is to silence the warning and check for NULL from x86_task_fpu(). However, that warning is fairly fresh and seems like a defense against misuse of the FPU state in kernel threads. Instead, stop outputting AVX-512_elapsed_ms for kernel threads altogether. The data was garbage anyway because avx512_timestamp is only updated for user threads, not kernel threads. If anyone ever wants to track kernel thread AVX-512 use, they can come back later and do it properly, separate from this bug fix. [ dhansen: mostly rewrite changelog ]
Product status
22aafe3bcb67472effdea1ccf0df20280192bbaf (git) before 2ca887e81095b99d890a8878841f36f4920181e6
22aafe3bcb67472effdea1ccf0df20280192bbaf (git) before 31cd31c9e17ece125aad27259501a2af69ccb020
6.16
Any version before 6.16
6.16.2 (semver)
6.17 (original_commit_for_fix)
References
git.kernel.org/...c/2ca887e81095b99d890a8878841f36f4920181e6
git.kernel.org/...c/31cd31c9e17ece125aad27259501a2af69ccb020
