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20 lines
3.1 KiB
Markdown
20 lines
3.1 KiB
Markdown
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### [CVE-2024-50275](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-50275)
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### Description
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In the Linux kernel, the following vulnerability has been resolved:arm64/sve: Discard stale CPU state when handling SVE trapsThe logic for handling SVE traps manipulates saved FPSIMD/SVE stateincorrectly, and a race with preemption can result in a task havingTIF_SVE set and TIF_FOREIGN_FPSTATE clear even though the live CPU stateis stale (e.g. with SVE traps enabled). This has been observed to resultin warnings from do_sve_acc() where SVE traps are not expected whileTIF_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/000000000000511e9a060ce5a45c@google.com/The race can occur when the SVE trap handler is preempted before andafter manipulating the saved FPSIMD/SVE state, starting and ending onthe 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 access shouldn't have trapped */|| sve_init_regs() {| if (!test_thread_flag(TIF_FOREIGN_FPSTATE)) {| ...| } else {| fpsimd_to_sve(current);| current->thread.fp_type = FP_STATE_SVE;| }| }|| put_cpu_fpsimd_context();|| // Preempted; migrated from CPU 1 to CPU 0.| // task->fpsimd_cpu is still 0| // If per_cpu_ptr(&fpsimd_last_state, 0) is still task then:| // - Stale HW state is reused (with SVE traps enabled)| // - TIF_FOREIGN_FPSTATE is cleared| // - A return to userspace skips HW state restore| }Fix the case where the state is not live and TIF_FOREIGN_FPSTATE is setby calling fpsimd_flush_task_state() to detach from the saved CPUstate. This ensures that a subsequent context switch will not reuse thestale CPU state, and will instead set TIF_FOREIGN_FPSTATE, forcing thenew state to be reloaded from memory prior to a return to userspace.
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### POC
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#### Reference
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No PoCs from references.
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#### Github
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- https://github.com/w4zu/Debian_security
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