CVE-2024-50275: arm64/sve: Discard stale CPU state when handling SVE traps
Description
In the Linux kernel, the following vulnerability has been resolved:
arm64/sve: Discard stale CPU state when handling SVE traps
The logic for handling SVE traps manipulates saved FPSIMD/SVE state
incorrectly, and a race with preemption can result in a task having
TIF_SVE set and TIF_FOREIGN_FPSTATE clear even though the live CPU state
is stale (e.g. with SVE traps enabled). This has been observed to result
in warnings from do_sve_acc() where SVE traps are not expected while
TIF_SVE is set:
| if (test_and_set_thread_flag(TIF_SVE))
| WARN_ON(1); /* SVE access shouldn't have trapped */
Warnings of this form have been reported intermittently, e.g.
https://lore.kernel.org/linux-arm-kernel/CA+G9fYtEGe_DhY2Ms7+L7NKsLYUomGsgqpdBj+QwDLeSg=JhGg@mail.gmail.com/
https://lore.kernel.org/linux-arm-kernel/[email protected]/
The race can occur when the SVE trap handler is preempted before and
after manipulating the saved FPSIMD/SVE state, starting and ending on
the same CPU, e.g.
| void do_sve_acc(unsigned long esr, struct pt_regs *regs)
| {
| // Trap on CPU 0 with TIF_SVE clear, SVE traps enabled
| // task->fpsimd_cpu is 0.
| // per_cpu_ptr(&fpsimd_last_state, 0) is task.
|
| ...
|
| // Preempted; migrated from CPU 0 to CPU 1.
| // TIF_FOREIGN_FPSTATE is set.
|
| get_cpu_fpsimd_context();
|
| if (test_and_set_thread_flag(TIF_SVE))
| WARN_ON(1); /* SVE ac...
Classification
CVE ID: CVE-2024-50275
Affected Products
Vendor: Linux
Product: Linux
Exploit Prediction Scoring System (EPSS)
EPSS Score: 0.04% (probability of being exploited)
EPSS Percentile: 5.08% (scored less or equal to compared to others)
EPSS Date: 2025-02-04 (when was this score calculated)
References
https://git.kernel.org/stable/c/51d3d80a6dc314982a9a0aeb0961085922a1aa15https://git.kernel.org/stable/c/de529504b3274d57caf8f66800b714b0d3ee235a
https://git.kernel.org/stable/c/51d11ea0250d6ee461987403bbfd4b2abb5613a7
https://git.kernel.org/stable/c/fa9ce027b3ce37a2bb173bf2553b5caa438fd8c9
https://git.kernel.org/stable/c/751ecf6afd6568adc98f2a6052315552c0483d18