From a5f7a5bb3b7f28ba7e4fa246775b29a0e5537255 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Tue, 8 Sep 2026 15:37:42 +0800 Subject: x86/kprobes: Fix crash when probing CS CALL instructions When using eBPF to probe CS CALL instructions within a function, a crash can be triggered. The eBPF tool probes offset 257 of the __hrtimer_run_queues() function: <__hrtimer_run_queues+249>: nopl 0x0(%rax,%rax,1) <__hrtimer_run_queues+254>: mov %r14,%rdi <__hrtimer_run_queues+257>: cs call <__x86_indirect_thunk_r12> <__hrtimer_run_queues+263>: mov %eax,%r12d <__hrtimer_run_queues+266>: xchg %ax,%ax <__hrtimer_run_queues+268>: mov %r13,%rdi Which triggers this crash: BUG: unable to handle page fault for address: 00000000000f41c9 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: 0002 [#1] SMP NOPTI CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P RIP: 0010:__hrtimer_run_queues+0x106/0x230 Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is at the 6th byte of the above CS CALL instruction. Since the CS CALL instruction occupies 6 bytes, the exception occurred in the middle of that call instruction. The root cause is that when using eBPF tools to probe in the middle of a function, a kprobe with INT3 is used as the underlying implementation. During single-step emulation of the original CALL instruction, int3_emulate_call() assumes that the probed CALL instruction is 5 bytes long. However, the actual CS-prefixed CALL instruction occupies 6 bytes, so it constructs an incorrect exception return address. When the CPU returns from the kprobe handler, the next instruction to be executed is at the address of the last byte of that CS CALL instruction. Coincidentally, starting from that address, the CPU fetches and decodes a completely different instruction, which ultimately triggers a kernel crash. Fix the issue by using the actual instruction length obtained from the instruction decoder when constructing the exception return address, rather than relying on the hardcoded CALL_INSN_SIZE macro. [ mingo: Refined the changelog ] Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step") Suggested-by: Masami Hiramatsu (Google) Signed-off-by: Jinke Han Signed-off-by: Ingo Molnar Reviewed-by: Masami Hiramatsu (Google) Acked-by: Yafang Shao Acked-by: Borislav Petkov Cc: Peter Zijlstra Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000 --- arch/um/os-Linux/process.c | 211 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 211 insertions(+) create mode 100644 arch/um/os-Linux/process.c (limited to 'arch/um/os-Linux/process.c') diff --git a/arch/um/os-Linux/process.c b/arch/um/os-Linux/process.c new file mode 100644 index 000000000..3a2a84ab9 --- /dev/null +++ b/arch/um/os-Linux/process.c @@ -0,0 +1,211 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de) + * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com) + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +void os_alarm_process(int pid) +{ + if (pid <= 0) + return; + + kill(pid, SIGALRM); +} + +void os_kill_process(int pid, int reap_child) +{ + if (pid <= 0) + return; + + /* Block signals until child is reaped */ + block_signals(); + + kill(pid, SIGKILL); + if (reap_child) + CATCH_EINTR(waitpid(pid, NULL, __WALL)); + + unblock_signals(); +} + +/* Kill off a ptraced child by all means available. kill it normally first, + * then PTRACE_KILL it, then PTRACE_CONT it in case it's in a run state from + * which it can't exit directly. + */ + +void os_kill_ptraced_process(int pid, int reap_child) +{ + if (pid <= 0) + return; + + /* Block signals until child is reaped */ + block_signals(); + + kill(pid, SIGKILL); + ptrace(PTRACE_KILL, pid); + ptrace(PTRACE_CONT, pid); + if (reap_child) + CATCH_EINTR(waitpid(pid, NULL, __WALL)); + + unblock_signals(); +} + +pid_t os_reap_child(void) +{ + int status; + + /* Try to reap a child */ + return waitpid(-1, &status, WNOHANG); +} + +/* Don't use the glibc version, which caches the result in TLS. It misses some + * syscalls, and also breaks with clone(), which does not unshare the TLS. + */ + +int os_getpid(void) +{ + return syscall(__NR_getpid); +} + +int os_map_memory(void *virt, int fd, unsigned long long off, unsigned long len, + int r, int w, int x) +{ + void *loc; + int prot; + + prot = (r ? PROT_READ : 0) | (w ? PROT_WRITE : 0) | + (x ? PROT_EXEC : 0); + + loc = mmap64((void *) virt, len, prot, MAP_SHARED | MAP_FIXED, + fd, off); + if (loc == MAP_FAILED) + return -errno; + return 0; +} + +int os_protect_memory(void *addr, unsigned long len, int r, int w, int x) +{ + int prot = ((r ? PROT_READ : 0) | (w ? PROT_WRITE : 0) | + (x ? PROT_EXEC : 0)); + + if (mprotect(addr, len, prot) < 0) + return -errno; + + return 0; +} + +int os_unmap_memory(void *addr, int len) +{ + int err; + + err = munmap(addr, len); + if (err < 0) + return -errno; + return 0; +} + +#ifndef MADV_REMOVE +#define MADV_REMOVE KERNEL_MADV_REMOVE +#endif + +int os_drop_memory(void *addr, int length) +{ + int err; + + err = madvise(addr, length, MADV_REMOVE); + if (err < 0) + err = -errno; + return err; +} + +int __init can_drop_memory(void) +{ + void *addr; + int fd, ok = 0; + + printk(UM_KERN_INFO "Checking host MADV_REMOVE support..."); + fd = create_mem_file(UM_KERN_PAGE_SIZE); + if (fd < 0) { + printk(UM_KERN_ERR "Creating test memory file failed, " + "err = %d\n", -fd); + goto out; + } + + addr = mmap64(NULL, UM_KERN_PAGE_SIZE, PROT_READ | PROT_WRITE, + MAP_SHARED, fd, 0); + if (addr == MAP_FAILED) { + printk(UM_KERN_ERR "Mapping test memory file failed, " + "err = %d\n", -errno); + goto out_close; + } + + if (madvise(addr, UM_KERN_PAGE_SIZE, MADV_REMOVE) != 0) { + printk(UM_KERN_ERR "MADV_REMOVE failed, err = %d\n", -errno); + goto out_unmap; + } + + printk(UM_KERN_CONT "OK\n"); + ok = 1; + +out_unmap: + munmap(addr, UM_KERN_PAGE_SIZE); +out_close: + close(fd); +out: + return ok; +} + +void init_new_thread_signals(void) +{ + set_handler(SIGSEGV); + set_handler(SIGTRAP); + set_handler(SIGFPE); + set_handler(SIGILL); + set_handler(SIGBUS); + signal(SIGHUP, SIG_IGN); + set_handler(SIGIO); + /* We (currently) only use the child reaper IRQ in seccomp mode */ + if (using_seccomp) + set_handler(SIGCHLD); + signal(SIGWINCH, SIG_IGN); +} + +void os_set_pdeathsig(void) +{ + prctl(PR_SET_PDEATHSIG, SIGKILL); +} + +int os_futex_wait(void *uaddr, unsigned int val) +{ + int r; + + CATCH_EINTR(r = syscall(__NR_futex, uaddr, FUTEX_WAIT, val, + NULL, NULL, 0)); + return r < 0 ? -errno : r; +} + +int os_futex_wake(void *uaddr) +{ + int r; + + CATCH_EINTR(r = syscall(__NR_futex, uaddr, FUTEX_WAKE, INT_MAX, + NULL, NULL, 0)); + return r < 0 ? -errno : r; +} -- cgit v1.3.1