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, 324 insertions, 0 deletions

diff --git a/io_uring/wait.c b/io_uring/wait.c
new file mode 100644
index 000000000..a48523c2f
--- /dev/null
+++ b/io_uring/wait.c
@@ -0,0 +1,324 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Waiting for completion events
+ */
+#include <linux/kernel.h>
+#include <linux/sched/signal.h>
+#include <linux/io_uring.h>
+#include <linux/time_namespace.h>
+
+#include <trace/events/io_uring.h>
+
+#include <uapi/linux/io_uring.h>
+
+#include "io_uring.h"
+#include "napi.h"
+#include "wait.h"
+
+static int io_wake_function(struct wait_queue_entry *curr, unsigned int mode,
+			    int wake_flags, void *key)
+{
+	struct io_wait_queue *iowq = container_of(curr, struct io_wait_queue, wq);
+
+	/*
+	 * Cannot safely flush overflowed CQEs from here, ensure we wake up
+	 * the task, and the next invocation will do it.
+	 */
+	if (io_should_wake(iowq) || io_has_work(iowq->ctx))
+		return autoremove_wake_function(curr, mode, wake_flags, key);
+	return -1;
+}
+
+int io_run_task_work_sig(struct io_ring_ctx *ctx)
+{
+	if (io_local_work_pending(ctx)) {
+		__set_current_state(TASK_RUNNING);
+		if (io_run_local_work(ctx, INT_MAX, IO_LOCAL_TW_DEFAULT_MAX) > 0)
+			return 0;
+	}
+	if (io_run_task_work() > 0)
+		return 0;
+	if (task_sigpending(current))
+		return -EINTR;
+	return 0;
+}
+
+static bool current_pending_io(void)
+{
+	struct io_uring_task *tctx = current->io_uring;
+
+	if (!tctx)
+		return false;
+	return percpu_counter_read_positive(&tctx->inflight);
+}
+
+static enum hrtimer_restart io_cqring_timer_wakeup(struct hrtimer *timer)
+{
+	struct io_wait_queue *iowq = container_of(timer, struct io_wait_queue, t);
+
+	WRITE_ONCE(iowq->hit_timeout, 1);
+	iowq->min_timeout = 0;
+	wake_up_process(iowq->wq.private);
+	return HRTIMER_NORESTART;
+}
+
+/*
+ * Doing min_timeout portion. If we saw any timeouts, events, or have work,
+ * wake up. If not, and we have a normal timeout, switch to that and keep
+ * sleeping.
+ */
+static enum hrtimer_restart io_cqring_min_timer_wakeup(struct hrtimer *timer)
+{
+	struct io_wait_queue *iowq = container_of(timer, struct io_wait_queue, t);
+	struct io_ring_ctx *ctx = iowq->ctx;
+
+	/* no general timeout, or shorter (or equal), we are done */
+	if (iowq->timeout == KTIME_MAX ||
+	    ktime_compare(iowq->min_timeout, iowq->timeout) >= 0)
+		goto out_wake;
+	/* work we may need to run, wake function will see if we need to wake */
+	if (io_has_work(ctx))
+		goto out_wake;
+	/* got events since we started waiting, min timeout is done */
+	scoped_guard(rcu) {
+		struct io_rings *rings = io_get_rings(ctx);
+
+		if (iowq->cq_min_tail != READ_ONCE(rings->cq.tail))
+			goto out_wake;
+		/* if we have any events and min timeout expired, we're done */
+		if (io_cqring_events(ctx))
+			goto out_wake;
+	}
+	/*
+	 * If using deferred task_work running and application is waiting on
+	 * more than one request, ensure we reset it now where we are switching
+	 * to normal sleeps. Any request completion post min_wait should wake
+	 * the task and return.
+	 */
+	if (ctx->flags & IORING_SETUP_DEFER_TASKRUN) {
+		atomic_set(&ctx->cq_wait_nr, 1);
+		smp_mb();
+		if (io_local_work_pending(ctx))
+			goto out_wake;
+	}
+
+	/* any generated CQE posted past this time should wake us up */
+	iowq->cq_tail = iowq->cq_min_tail + 1;
+
+	hrtimer_update_function(&iowq->t, io_cqring_timer_wakeup);
+	hrtimer_set_expires(timer, iowq->timeout);
+	return HRTIMER_RESTART;
+out_wake:
+	return io_cqring_timer_wakeup(timer);
+}
+
+static int io_cqring_schedule_timeout(struct io_wait_queue *iowq,
+				      clockid_t clock_id, ktime_t start_time)
+{
+	ktime_t timeout;
+
+	if (iowq->min_timeout) {
+		timeout = ktime_add_ns(iowq->min_timeout, start_time);
+		hrtimer_setup_on_stack(&iowq->t, io_cqring_min_timer_wakeup, clock_id,
+				       HRTIMER_MODE_ABS);
+	} else {
+		timeout = iowq->timeout;
+		hrtimer_setup_on_stack(&iowq->t, io_cqring_timer_wakeup, clock_id,
+				       HRTIMER_MODE_ABS);
+	}
+
+	hrtimer_set_expires_range_ns(&iowq->t, timeout, 0);
+	hrtimer_start_expires(&iowq->t, HRTIMER_MODE_ABS);
+
+	if (!READ_ONCE(iowq->hit_timeout))
+		schedule();
+
+	hrtimer_cancel(&iowq->t);
+	destroy_hrtimer_on_stack(&iowq->t);
+	__set_current_state(TASK_RUNNING);
+
+	return READ_ONCE(iowq->hit_timeout) ? -ETIME : 0;
+}
+
+static int __io_cqring_wait_schedule(struct io_ring_ctx *ctx,
+				     struct io_wait_queue *iowq,
+				     struct ext_arg *ext_arg,
+				     ktime_t start_time)
+{
+	int ret = 0;
+
+	/*
+	 * Mark us as being in io_wait if we have pending requests, so cpufreq
+	 * can take into account that the task is waiting for IO - turns out
+	 * to be important for low QD IO.
+	 */
+	if (ext_arg->iowait && current_pending_io())
+		current->in_iowait = 1;
+	if (iowq->timeout != KTIME_MAX || iowq->min_timeout)
+		ret = io_cqring_schedule_timeout(iowq, ctx->clockid, start_time);
+	else
+		schedule();
+	current->in_iowait = 0;
+	return ret;
+}
+
+/* If this returns > 0, the caller should retry */
+static inline int io_cqring_wait_schedule(struct io_ring_ctx *ctx,
+					  struct io_wait_queue *iowq,
+					  struct ext_arg *ext_arg,
+					  ktime_t start_time)
+{
+	if (unlikely(READ_ONCE(ctx->check_cq)))
+		return 1;
+	if (unlikely(io_local_work_pending(ctx)))
+		return 1;
+	if (unlikely(task_work_pending(current)))
+		return 1;
+	if (unlikely(task_sigpending(current)))
+		return -EINTR;
+	if (unlikely(io_should_wake(iowq)))
+		return 0;
+
+	return __io_cqring_wait_schedule(ctx, iowq, ext_arg, start_time);
+}
+
+/*
+ * Wait until events become available, if we don't already have some. The
+ * application must reap them itself, as they reside on the shared cq ring.
+ */
+int io_cqring_wait(struct io_ring_ctx *ctx, int min_events, u32 flags,
+		   struct ext_arg *ext_arg)
+{
+	struct io_wait_queue iowq;
+	struct io_rings *rings;
+	ktime_t start_time;
+	int ret, nr_wait;
+
+	min_events = min_t(int, min_events, ctx->cq_entries);
+
+	if (!io_allowed_run_tw(ctx))
+		return -EEXIST;
+	if (io_local_work_pending(ctx))
+		io_run_local_work(ctx, min_events,
+				  max(IO_LOCAL_TW_DEFAULT_MAX, min_events));
+	io_run_task_work();
+
+	if (unlikely(test_bit(IO_CHECK_CQ_OVERFLOW_BIT, &ctx->check_cq)))
+		io_cqring_do_overflow_flush(ctx);
+
+	rcu_read_lock();
+	rings = io_get_rings(ctx);
+	if (__io_cqring_events_user(ctx) >= min_events) {
+		rcu_read_unlock();
+		return 0;
+	}
+
+	init_waitqueue_func_entry(&iowq.wq, io_wake_function);
+	iowq.wq.private = current;
+	INIT_LIST_HEAD(&iowq.wq.entry);
+	iowq.ctx = ctx;
+	iowq.cq_tail = READ_ONCE(rings->cq.head) + min_events;
+	iowq.cq_min_tail = READ_ONCE(rings->cq.tail);
+	nr_wait = (int) iowq.cq_tail - READ_ONCE(rings->cq.tail);
+	rcu_read_unlock();
+	rings = NULL;
+	iowq.nr_timeouts = atomic_read(&ctx->cq_timeouts);
+	iowq.hit_timeout = 0;
+	iowq.min_timeout = ext_arg->min_time;
+	iowq.timeout = KTIME_MAX;
+	start_time = io_get_time(ctx);
+
+	if (ext_arg->ts_set) {
+		iowq.timeout = timespec64_to_ktime(ext_arg->ts);
+		if (flags & IORING_ENTER_ABS_TIMER)
+			iowq.timeout = timens_ktime_to_host(ctx->clockid,
+							    iowq.timeout);
+		else
+			iowq.timeout = ktime_add(iowq.timeout, start_time);
+	}
+
+	if (ext_arg->sig) {
+#ifdef CONFIG_COMPAT
+		if (in_compat_syscall())
+			ret = set_compat_user_sigmask((const compat_sigset_t __user *)ext_arg->sig,
+						      ext_arg->argsz);
+		else
+#endif
+			ret = set_user_sigmask(ext_arg->sig, ext_arg->argsz);
+
+		if (ret)
+			return ret;
+	}
+
+	io_napi_busy_loop(ctx, &iowq);
+
+	trace_io_uring_cqring_wait(ctx, min_events);
+	do {
+		unsigned long check_cq;
+
+		if (ctx->flags & IORING_SETUP_DEFER_TASKRUN) {
+			atomic_set(&ctx->cq_wait_nr, nr_wait);
+			set_current_state(TASK_INTERRUPTIBLE);
+		} else {
+			prepare_to_wait_exclusive(&ctx->cq_wait, &iowq.wq,
+							TASK_INTERRUPTIBLE);
+		}
+
+		ret = io_cqring_wait_schedule(ctx, &iowq, ext_arg, start_time);
+		__set_current_state(TASK_RUNNING);
+		atomic_set(&ctx->cq_wait_nr, IO_CQ_WAKE_INIT);
+
+		/*
+		 * Run task_work after scheduling and before io_should_wake().
+		 * If we got woken because of task_work being processed, run it
+		 * now rather than let the caller do another wait loop.
+		 */
+		if (io_local_work_pending(ctx))
+			io_run_local_work(ctx, nr_wait, nr_wait);
+		io_run_task_work();
+
+		/*
+		 * Non-local task_work will be run on exit to userspace, but
+		 * if we're using DEFER_TASKRUN, then we could have waited
+		 * with a timeout for a number of requests. If the timeout
+		 * hits, we could have some requests ready to process. Ensure
+		 * this break is _after_ we have run task_work, to avoid
+		 * deferring running potentially pending requests until the
+		 * next time we wait for events.
+		 */
+		if (ret < 0)
+			break;
+
+		check_cq = READ_ONCE(ctx->check_cq);
+		if (unlikely(check_cq)) {
+			/* let the caller flush overflows, retry */
+			if (check_cq & BIT(IO_CHECK_CQ_OVERFLOW_BIT))
+				io_cqring_do_overflow_flush(ctx);
+			if (check_cq & BIT(IO_CHECK_CQ_DROPPED_BIT)) {
+				ret = -EBADR;
+				break;
+			}
+		}
+
+		if (io_should_wake(&iowq)) {
+			ret = 0;
+			break;
+		}
+		cond_resched();
+
+		/* if min timeout has been hit, don't reset wait count */
+		if (!iowq.hit_timeout)
+			scoped_guard(rcu)
+				nr_wait = (int) iowq.cq_tail -
+						READ_ONCE(io_get_rings(ctx)->cq.tail);
+		else
+			nr_wait = 1;
+	} while (1);
+
+	if (!(ctx->flags & IORING_SETUP_DEFER_TASKRUN))
+		finish_wait(&ctx->cq_wait, &iowq.wq);
+	restore_saved_sigmask_unless(ret == -EINTR);
+
+	guard(rcu)();
+	return READ_ONCE(io_get_rings(ctx)->cq.head) == READ_ONCE(io_get_rings(ctx)->cq.tail) ? ret : 0;
+}