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 --- drivers/dma-buf/sync_debug.c | 124 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 124 insertions(+) create mode 100644 drivers/dma-buf/sync_debug.c (limited to 'drivers/dma-buf/sync_debug.c') diff --git a/drivers/dma-buf/sync_debug.c b/drivers/dma-buf/sync_debug.c new file mode 100644 index 000000000..9e5d662cd --- /dev/null +++ b/drivers/dma-buf/sync_debug.c @@ -0,0 +1,124 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Sync File validation framework and debug information + * + * Copyright (C) 2012 Google, Inc. + */ + +#include +#include "sync_debug.h" + +static struct dentry *dbgfs; + +static LIST_HEAD(sync_timeline_list_head); +static DEFINE_SPINLOCK(sync_timeline_list_lock); + +void sync_timeline_debug_add(struct sync_timeline *obj) +{ + unsigned long flags; + + spin_lock_irqsave(&sync_timeline_list_lock, flags); + list_add_tail(&obj->sync_timeline_list, &sync_timeline_list_head); + spin_unlock_irqrestore(&sync_timeline_list_lock, flags); +} + +void sync_timeline_debug_remove(struct sync_timeline *obj) +{ + unsigned long flags; + + spin_lock_irqsave(&sync_timeline_list_lock, flags); + list_del(&obj->sync_timeline_list); + spin_unlock_irqrestore(&sync_timeline_list_lock, flags); +} + +static const char *sync_status_str(int status) +{ + if (status < 0) + return "error"; + + if (status > 0) + return "signaled"; + + return "active"; +} + +static void sync_print_fence(struct seq_file *s, + struct dma_fence *fence, bool show) +{ + struct sync_timeline *parent = dma_fence_parent(fence); + int status; + + status = dma_fence_get_status_locked(fence); + + seq_printf(s, " %s%sfence %s", + show ? parent->name : "", + show ? "_" : "", + sync_status_str(status)); + + if (test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags)) { + struct timespec64 ts64 = + ktime_to_timespec64(fence->timestamp); + + seq_printf(s, "@%ptSp", &ts64); + } + + seq_printf(s, ": %lld", fence->seqno); + seq_printf(s, " / %d", parent->value); + seq_putc(s, '\n'); +} + +static void sync_print_obj(struct seq_file *s, struct sync_timeline *obj) +{ + struct list_head *pos; + + seq_printf(s, "%s: %d\n", obj->name, obj->value); + + spin_lock(&obj->lock); /* Caller already disabled IRQ. */ + list_for_each(pos, &obj->pt_list) { + struct sync_pt *pt = container_of(pos, struct sync_pt, link); + sync_print_fence(s, &pt->base, false); + } + spin_unlock(&obj->lock); +} + +static int sync_info_debugfs_show(struct seq_file *s, void *unused) +{ + struct list_head *pos; + + seq_puts(s, "objs:\n--------------\n"); + + spin_lock_irq(&sync_timeline_list_lock); + list_for_each(pos, &sync_timeline_list_head) { + struct sync_timeline *obj = + container_of(pos, struct sync_timeline, + sync_timeline_list); + + sync_print_obj(s, obj); + seq_putc(s, '\n'); + } + spin_unlock_irq(&sync_timeline_list_lock); + + seq_puts(s, "fences:\n--------------\n"); + + return 0; +} + +DEFINE_SHOW_ATTRIBUTE(sync_info_debugfs); + +static __init int sync_debugfs_init(void) +{ + dbgfs = debugfs_create_dir("sync", NULL); + + /* + * The debugfs files won't ever get removed and thus, there is + * no need to protect it against removal races. The use of + * debugfs_create_file_unsafe() is actually safe here. + */ + debugfs_create_file_unsafe("info", 0444, dbgfs, NULL, + &sync_info_debugfs_fops); + debugfs_create_file_unsafe("sw_sync", 0644, dbgfs, NULL, + &sw_sync_debugfs_fops); + + return 0; +} +late_initcall(sync_debugfs_init); -- cgit v1.3.1