x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

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) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 360 insertions, 0 deletions

diff --git a/io_uring/tw.c b/io_uring/tw.c
new file mode 100644
index 000000000..f573bcc3a
--- /dev/null
+++ b/io_uring/tw.c
@@ -0,0 +1,360 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Task work handling for io_uring
+ */
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/sched/signal.h>
+#include <linux/io_uring.h>
+#include <linux/indirect_call_wrapper.h>
+
+#include "io_uring.h"
+#include "tctx.h"
+#include "poll.h"
+#include "rw.h"
+#include "eventfd.h"
+#include "wait.h"
+#include "mpscq.h"
+
+static void ctx_flush_and_put(struct io_ring_ctx *ctx, io_tw_token_t tw)
+{
+	if (!ctx)
+		return;
+	if (ctx->flags & IORING_SETUP_TASKRUN_FLAG)
+		atomic_andnot(IORING_SQ_TASKRUN, &ctx->rings->sq_flags);
+
+	io_submit_flush_completions(ctx);
+	mutex_unlock(&ctx->uring_lock);
+	percpu_ref_put(&ctx->refs);
+}
+
+void io_tctx_fallback_work(struct work_struct *work)
+{
+	struct io_uring_task *tctx = container_of(work, struct io_uring_task,
+						  fallback_work);
+	unsigned int count = 0;
+
+	/*
+	 * Run the entries directly. We're in PF_KTHRED context, hence
+	 * io_should_terminate_tw() is true and they will be marked as
+	 * canceled.
+	 */
+	tctx_task_work_run(tctx, UINT_MAX, &count);
+	put_task_struct(tctx->task);
+}
+
+static void io_fallback_tw(struct io_uring_task *tctx)
+{
+	/*
+	 * The task ref both keeps ->task valid and, as __io_uring_free() is
+	 * only called when the task itself is freed, ensures the tctx (and
+	 * the queued work) stay around until the drain has run.
+	 */
+	get_task_struct(tctx->task);
+	if (!queue_work(system_dfl_wq, &tctx->fallback_work))
+		put_task_struct(tctx->task);
+}
+
+/*
+ * Run queued task_work, processing no more than max_entries, with the number
+ * of entries processed added to *count. If more entries than max_entries are
+ * available, the remainder simply stay on the queue for the next run.
+ */
+void tctx_task_work_run(struct io_uring_task *tctx, unsigned int max_entries,
+			unsigned int *count)
+{
+	struct io_ring_ctx *ctx = NULL;
+	struct io_tw_state ts = { };
+
+	while (*count < max_entries) {
+		struct llist_node *node = mpscq_pop(&tctx->task_list,
+						    &tctx->task_head);
+		struct io_kiocb *req;
+
+		if (!node) {
+			if (mpscq_empty(&tctx->task_list))
+				break;
+			/*
+			 * A producer has published a node but hasn't
+			 * linked it into the queue yet (see mpscq_pop()).
+			 * Give it a chance to finish rather than spinning,
+			 * and don't sit on the ctx lock while doing so.
+			 */
+			ctx_flush_and_put(ctx, ts);
+			ctx = NULL;
+			cond_resched();
+			continue;
+		}
+		req = container_of(node, struct io_kiocb, io_task_work.node);
+		if (req->ctx != ctx) {
+			ctx_flush_and_put(ctx, ts);
+			ctx = req->ctx;
+			mutex_lock(&ctx->uring_lock);
+			percpu_ref_get(&ctx->refs);
+			ts.cancel = io_should_terminate_tw(ctx);
+		}
+		INDIRECT_CALL_2(req->io_task_work.func,
+				io_poll_task_func, io_req_rw_complete,
+				(struct io_tw_req){req}, ts);
+		(*count)++;
+		/*
+		 * Break if most recent pop emptied the queue. This helps
+		 * bound task_work run, and also protects the regular
+		 * task_work addition.
+		 */
+		if (mpscq_pop_emptied(&tctx->task_list, tctx->task_head))
+			break;
+		if (unlikely(need_resched())) {
+			ctx_flush_and_put(ctx, ts);
+			ctx = NULL;
+			cond_resched();
+		}
+	}
+	ctx_flush_and_put(ctx, ts);
+
+	/*
+	 * Relaxed read is enough as only the task itself sets ->in_cancel.
+	 * The tctx may also be drained by io_tctx_fallback_work(), in which
+	 * case current is a kworker that has no tctx refs to drop.
+	 */
+	if (unlikely(atomic_read(&tctx->in_cancel)) &&
+	    current->io_uring == tctx)
+		io_uring_drop_tctx_refs(current);
+
+	trace_io_uring_task_work_run(tctx, *count);
+}
+
+void tctx_task_work(struct callback_head *cb)
+{
+	struct io_uring_task *tctx;
+	unsigned int count = 0;
+
+	tctx = container_of(cb, struct io_uring_task, task_work);
+	tctx_task_work_run(tctx, UINT_MAX, &count);
+}
+
+/*
+ * Sets IORING_SQ_TASKRUN in the sq_flags shared with userspace, using the
+ * RCU protected rings pointer to be safe against concurrent ring resizing.
+ */
+static void io_ctx_mark_taskrun(struct io_ring_ctx *ctx)
+{
+	lockdep_assert_in_rcu_read_lock();
+
+	if (ctx->flags & IORING_SETUP_TASKRUN_FLAG) {
+		struct io_rings *rings = rcu_dereference(ctx->rings_rcu);
+
+		atomic_or(IORING_SQ_TASKRUN, &rings->sq_flags);
+	}
+}
+
+void io_req_local_work_add(struct io_kiocb *req, unsigned flags)
+{
+	struct io_ring_ctx *ctx = req->ctx;
+	int nr_wait;
+
+	/* pairs with synchronize_rcu() in io_ring_exit_work() */
+	guard(rcu)();
+
+	/*
+	 * We don't know how many requests there are in the link and whether
+	 * they can even be queued lazily, fall back to non-lazy.
+	 */
+	if (req->flags & IO_REQ_LINK_FLAGS)
+		flags &= ~IOU_F_TWQ_LAZY_WAKE;
+
+	/*
+	 * The xchg() in mpscq_push() implies a full barrier, which pairs with
+	 * the barrier in set_current_state() on the io_cqring_wait() side. This
+	 * ensures that either we see the updated ->cq_wait_nr, or waiters going
+	 * to sleep will observe the work added to the list, which is similar to
+	 * the wait/wake task state sync.
+	 */
+	if (mpscq_push(&ctx->work_list, &req->io_task_work.node)) {
+		io_ctx_mark_taskrun(ctx);
+		if (data_race(ctx->int_flags) & IO_RING_F_HAS_EVFD)
+			io_eventfd_signal(ctx, false, flags & IOU_F_TWQ_IN_WAKE);
+	}
+
+	/*
+	 * No one is waiting (IO_CQ_WAKE_INIT), or this cycle's wake up has
+	 * already been issued (zero or negative, see below).
+	 */
+	nr_wait = atomic_read(&ctx->cq_wait_nr);
+	if (nr_wait <= 0)
+		return;
+	if (flags & IOU_F_TWQ_LAZY_WAKE) {
+		/*
+		 * ->cq_wait_nr counts down the number of lazy adds, once it
+		 * hits zero we're good to wake the waiter. A producer that
+		 * gets delayed between pushing its entry and getting here
+		 * may count down a later wait cycle. That's OK, it'll be an
+		 * early wake, not a lost one.
+		 */
+		if (!atomic_dec_and_test(&ctx->cq_wait_nr))
+			return;
+	} else if (atomic_xchg(&ctx->cq_wait_nr, IO_CQ_WAKE_INIT) <= 0) {
+		/*
+		 * Potentially raced with lazy add, claim the wake. A value
+		 * <= 0 means a lazy add hit zero or another forced add
+		 * claimed IO_CQ_WAKE_INIT. Either way, the wake up for this
+		 * wait cycle has already been done.
+		 */
+		return;
+	}
+	wake_up_state(ctx->submitter_task, TASK_INTERRUPTIBLE);
+}
+
+void io_req_normal_work_add(struct io_kiocb *req)
+{
+	struct io_uring_task *tctx = req->tctx;
+	struct io_ring_ctx *ctx = req->ctx;
+
+	/* tw run already pending, nothing else to do */
+	if (!mpscq_push(&tctx->task_list, &req->io_task_work.node))
+		return;
+
+	/*
+	 * Doesn't need to use ->rings_rcu, as resizing isn't supported for
+	 * !DEFER_TASKRUN.
+	 */
+	if (ctx->flags & IORING_SETUP_TASKRUN_FLAG)
+		atomic_or(IORING_SQ_TASKRUN, &ctx->rings->sq_flags);
+
+	/* SQPOLL doesn't need the task_work added, it'll run it itself */
+	if (ctx->flags & IORING_SETUP_SQPOLL) {
+		__set_notify_signal(tctx->task);
+		return;
+	}
+
+	if (likely(!task_work_add(tctx->task, &tctx->task_work, ctx->notify_method)))
+		return;
+
+	io_fallback_tw(tctx);
+}
+
+void io_req_task_work_add_remote(struct io_kiocb *req, unsigned flags)
+{
+	if (WARN_ON_ONCE(!(req->ctx->flags & IORING_SETUP_DEFER_TASKRUN)))
+		return;
+	__io_req_task_work_add(req, flags);
+}
+
+void __cold io_cancel_local_task_work(struct io_ring_ctx *ctx)
+{
+	struct io_tw_state ts = { .cancel = true };
+	struct llist_node *node;
+
+	/*
+	 * The work list consumer side is serialized by ->uring_lock, see
+	 * __io_run_local_work(). Grab it to guard against racing with normal
+	 * task_work running, as the task may be exiting. The ring is going
+	 * away, run the entries in cancel mode right here - the callers
+	 * provide the same process context the per-ctx fallback work that
+	 * they were previously punted to ran in.
+	 */
+	guard(mutex)(&ctx->uring_lock);
+
+	while (!mpscq_empty(&ctx->work_list)) {
+		struct io_kiocb *req;
+
+		node = mpscq_pop(&ctx->work_list, &ctx->work_head);
+		if (!node) {
+			/* a producer is mid-push, wait for it to link */
+			cond_resched();
+			continue;
+		}
+		req = container_of(node, struct io_kiocb, io_task_work.node);
+		req->io_task_work.func((struct io_tw_req){req}, ts);
+	}
+	io_submit_flush_completions(ctx);
+}
+
+static bool io_run_local_work_continue(struct io_ring_ctx *ctx, int events,
+				       int min_events)
+{
+	if (!io_local_work_pending(ctx))
+		return false;
+	if (events < min_events)
+		return true;
+	if (ctx->flags & IORING_SETUP_TASKRUN_FLAG)
+		atomic_or(IORING_SQ_TASKRUN, &ctx->rings->sq_flags);
+	return false;
+}
+
+static int __io_run_local_work_loop(struct io_ring_ctx *ctx,
+				    io_tw_token_t tw,
+				    int events)
+{
+	int ret = 0;
+
+	while (ret < events) {
+		struct llist_node *node = mpscq_pop(&ctx->work_list, &ctx->work_head);
+		struct io_kiocb *req;
+
+		if (!node)
+			break;
+		req = container_of(node, struct io_kiocb, io_task_work.node);
+		INDIRECT_CALL_2(req->io_task_work.func,
+				io_poll_task_func, io_req_rw_complete,
+				(struct io_tw_req){req}, tw);
+		ret++;
+	}
+
+	return ret;
+}
+
+static int __io_run_local_work(struct io_ring_ctx *ctx, io_tw_token_t tw,
+			       int min_events, int max_events)
+{
+	unsigned int loops = 0;
+	int ret = 0;
+
+	if (WARN_ON_ONCE(ctx->submitter_task != current))
+		return -EEXIST;
+	if (ctx->flags & IORING_SETUP_TASKRUN_FLAG)
+		atomic_andnot(IORING_SQ_TASKRUN, &ctx->rings->sq_flags);
+again:
+	/*
+	 * If the last loop made no progress while work is still pending,
+	 * a producer has published a node but hasn't linked it into the
+	 * queue yet (see mpscq_pop()). Give it a chance to finish rather
+	 * than spinning on the queue.
+	 */
+	if (unlikely(loops && !ret))
+		cond_resched();
+	tw.cancel = io_should_terminate_tw(ctx);
+	min_events -= ret;
+	ret = __io_run_local_work_loop(ctx, tw, max_events);
+	loops++;
+
+	if (io_run_local_work_continue(ctx, ret, min_events))
+		goto again;
+	io_submit_flush_completions(ctx);
+	if (io_run_local_work_continue(ctx, ret, min_events))
+		goto again;
+
+	trace_io_uring_local_work_run(ctx, ret, loops);
+	return ret;
+}
+
+int io_run_local_work_locked(struct io_ring_ctx *ctx, int min_events)
+{
+	struct io_tw_state ts = {};
+
+	if (!io_local_work_pending(ctx))
+		return 0;
+	return __io_run_local_work(ctx, ts, min_events,
+					max(IO_LOCAL_TW_DEFAULT_MAX, min_events));
+}
+
+int io_run_local_work(struct io_ring_ctx *ctx, int min_events, int max_events)
+{
+	struct io_tw_state ts = {};
+	int ret;
+
+	mutex_lock(&ctx->uring_lock);
+	ret = __io_run_local_work(ctx, ts, min_events, max_events);
+	mutex_unlock(&ctx->uring_lock);
+	return ret;
+}