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 --- io_uring/napi.h | 90 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 90 insertions(+) create mode 100644 io_uring/napi.h (limited to 'io_uring/napi.h') diff --git a/io_uring/napi.h b/io_uring/napi.h new file mode 100644 index 000000000..e0aecccc5 --- /dev/null +++ b/io_uring/napi.h @@ -0,0 +1,90 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#ifndef IOU_NAPI_H +#define IOU_NAPI_H + +#include +#include +#include + +#ifdef CONFIG_NET_RX_BUSY_POLL + +void io_napi_init(struct io_ring_ctx *ctx); +void io_napi_free(struct io_ring_ctx *ctx); + +int io_register_napi(struct io_ring_ctx *ctx, void __user *arg); +int io_unregister_napi(struct io_ring_ctx *ctx, void __user *arg); + +int __io_napi_add_id(struct io_ring_ctx *ctx, unsigned int napi_id, + unsigned int mode); + +void __io_napi_busy_loop(struct io_ring_ctx *ctx, struct io_wait_queue *iowq); +int io_napi_sqpoll_busy_poll(struct io_ring_ctx *ctx); + +static inline bool io_napi(struct io_ring_ctx *ctx) +{ + return !list_empty(&ctx->napi_list); +} + +static inline void io_napi_busy_loop(struct io_ring_ctx *ctx, + struct io_wait_queue *iowq) +{ + if (!io_napi(ctx)) + return; + __io_napi_busy_loop(ctx, iowq); +} + +/* + * io_napi_add() - Add napi id to the busy poll list + * @req: pointer to io_kiocb request + * + * Add the napi id of the socket to the napi busy poll list and hash table. + */ +static inline void io_napi_add(struct io_kiocb *req) +{ + struct io_ring_ctx *ctx = req->ctx; + struct socket *sock; + unsigned int mode = IO_URING_NAPI_TRACKING_DYNAMIC; + + if (READ_ONCE(ctx->napi_track_mode) != mode) + return; + + sock = sock_from_file(req->file); + if (sock && sock->sk) + __io_napi_add_id(ctx, READ_ONCE(sock->sk->sk_napi_id), mode); +} + +#else + +static inline void io_napi_init(struct io_ring_ctx *ctx) +{ +} +static inline void io_napi_free(struct io_ring_ctx *ctx) +{ +} +static inline int io_register_napi(struct io_ring_ctx *ctx, void __user *arg) +{ + return -EOPNOTSUPP; +} +static inline int io_unregister_napi(struct io_ring_ctx *ctx, void __user *arg) +{ + return -EOPNOTSUPP; +} +static inline bool io_napi(struct io_ring_ctx *ctx) +{ + return false; +} +static inline void io_napi_add(struct io_kiocb *req) +{ +} +static inline void io_napi_busy_loop(struct io_ring_ctx *ctx, + struct io_wait_queue *iowq) +{ +} +static inline int io_napi_sqpoll_busy_poll(struct io_ring_ctx *ctx) +{ + return 0; +} +#endif /* CONFIG_NET_RX_BUSY_POLL */ + +#endif -- cgit v1.3.1