Vulnerability CVE-2023-52598
Published: 2024-03-06

Description:
In the Linux kernel, the following vulnerability has been resolved:

s390/ptrace: handle setting of fpc register correctly

If the content of the floating point control (fpc) register of a traced
process is modified with the ptrace interface the new value is tested for
validity by temporarily loading it into the fpc register.

This may lead to corruption of the fpc register of the tracing process:
if an interrupt happens while the value is temporarily loaded into the
fpc register, and within interrupt context floating point or vector
registers are used, the current fp/vx registers are saved with
save_fpu_regs() assuming they belong to user space and will be loaded into
fp/vx registers when returning to user space.

test_fp_ctl() restores the original user space fpc register value, however
it will be discarded, when returning to user space.

In result the tracer will incorrectly continue to run with the value that
was supposed to be used for the traced process.

Fix this by saving fpu register contents with save_fpu_regs() before using
test_fp_ctl().

 References:
https://git.kernel.org/stable/c/6ccf904aac0292e1f6b1a1be6c407c414f7cf713
https://git.kernel.org/stable/c/6d0822f2cc9b153bf2df49a84599195a2e0d21a8
https://git.kernel.org/stable/c/856caf2730ea18cb39e95833719c02a02447dc0a
https://git.kernel.org/stable/c/28a1f492cb527f64593457a0a0f0d809b3f36c25
https://git.kernel.org/stable/c/7a4d6481fbdd661f9e40e95febb95e3dee82bad3
https://git.kernel.org/stable/c/02c6bbfb08bad78dd014e24c7b893723c15ec7a1
https://git.kernel.org/stable/c/bdce67df7f12fb0409fbc604ce7c4254703f56d4
https://git.kernel.org/stable/c/8b13601d19c541158a6e18b278c00ba69ae37829
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