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20 lines
2.7 KiB
Markdown
20 lines
2.7 KiB
Markdown
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### [CVE-2024-35871](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-35871)
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### Description
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In the Linux kernel, the following vulnerability has been resolved:riscv: process: Fix kernel gp leakagechildregs represents the registers which are active for the new threadin user context. For a kernel thread, childregs->gp is never used sincethe kernel gp is not touched by switch_to. For a user mode helper, thegp value can be observed in user space after execve or possibly by othermeans.[From the email thread]The /* Kernel thread */ comment is somewhat inaccurate in that it is also usedfor user_mode_helper threads, which exec a user process, e.g. /sbin/init orwhen /proc/sys/kernel/core_pattern is a pipe. Such threads do not havePF_KTHREAD set and are valid targets for ptrace etc. even before they exec.childregs is the *user* context during syscall execution and it is observablefrom userspace in at least five ways:1. kernel_execve does not currently clear integer registers, so the starting register state for PID 1 and other user processes started by the kernel has sp = user stack, gp = kernel __global_pointer$, all other integer registers zeroed by the memset in the patch comment. This is a bug in its own right, but I'm unwilling to bet that it is the only way to exploit the issue addressed by this patch.2. ptrace(PTRACE_GETREGSET): you can PTRACE_ATTACH to a user_mode_helper thread before it execs, but ptrace requires SIGSTOP to be delivered which can only happen at user/kernel boundaries.3. /proc/*/task/*/syscall: this is perfectly happy to read pt_regs for user_mode_helpers before the exec completes, but gp is not one of the registers it returns.4. PERF_SAMPLE_REGS_USER: LOCKDOWN_PERF normally prevents access to kernel addresses via PERF_SAMPLE_REGS_INTR, but due to this bug kernel addresses are also exposed via PERF_SAMPLE_REGS_USER which is permitted under LOCKDOWN_PERF. I have not attempted to write exploit code.5. Much of the tracing infrastructure allows access to user registers. I have not attempted to determine which forms of tracing allow access to user registers without already allowing access to kernel registers.
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### POC
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#### Reference
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- https://git.kernel.org/stable/c/d14fa1fcf69db9d070e75f1c4425211fa619dfc8
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#### Github
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No PoCs found on GitHub currently.
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