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2297554f01
irq_fpu_usable() incorrectly returned true before the FPU is
initialized. The x86 CPU onlining code can call sha256() to checksum
AMD microcode images, before the FPU is initialized. Since sha256()
recently gained a kernel-mode FPU optimized code path, a crash occurred
in kernel_fpu_begin_mask() during hotplug CPU onlining.
(The crash did not occur during boot-time CPU onlining, since the
optimized sha256() code is not enabled until subsys_initcalls run.)
Fix this by making irq_fpu_usable() return false before fpu__init_cpu()
has run. To do this without adding any additional overhead to
irq_fpu_usable(), replace the existing per-CPU bool in_kernel_fpu with
kernel_fpu_allowed which tracks both initialization and usage rather
than just usage. The initial state is false; FPU initialization sets it
to true; kernel-mode FPU sections toggle it to false and then back to
true; and CPU offlining restores it to the initial state of false.
Fixes: 11d7956d52 ("crypto: x86/sha256 - implement library instead of shash")
Reported-by: Ayush Jain <Ayush.Jain3@amd.com>
Closes: https://lore.kernel.org/r/20250516112217.GBaCcf6Yoc6LkIIryP@fat_crate.local
Signed-off-by: Eric Biggers <ebiggers@google.com>
Tested-by: Ayush Jain <Ayush.Jain3@amd.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.