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, 413 insertions, 0 deletions

diff --git a/drivers/tty/tty_ldsem.c b/drivers/tty/tty_ldsem.c
new file mode 100644
index 000000000..4e18031a5
--- /dev/null
+++ b/drivers/tty/tty_ldsem.c
@@ -0,0 +1,413 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Ldisc rw semaphore
+ *
+ * The ldisc semaphore is semantically a rw_semaphore but which enforces
+ * an alternate policy, namely:
+ *   1) Supports lock wait timeouts
+ *   2) Write waiter has priority
+ *   3) Downgrading is not supported
+ *
+ * Implementation notes:
+ *   1) Upper half of semaphore count is a wait count (differs from rwsem
+ *	in that rwsem normalizes the upper half to the wait bias)
+ *   2) Lacks overflow checking
+ *
+ * The generic counting was copied and modified from include/asm-generic/rwsem.h
+ * by Paul Mackerras <paulus@samba.org>.
+ *
+ * The scheduling policy was copied and modified from lib/rwsem.c
+ * Written by David Howells (dhowells@redhat.com).
+ *
+ * This implementation incorporates the write lock stealing work of
+ * Michel Lespinasse <walken@google.com>.
+ *
+ * Copyright (C) 2013 Peter Hurley <peter@hurleysoftware.com>
+ */
+
+#include <linux/list.h>
+#include <linux/spinlock.h>
+#include <linux/atomic.h>
+#include <linux/tty.h>
+#include <linux/sched.h>
+#include <linux/sched/debug.h>
+#include <linux/sched/task.h>
+
+
+#if BITS_PER_LONG == 64
+# define LDSEM_ACTIVE_MASK	0xffffffffL
+#else
+# define LDSEM_ACTIVE_MASK	0x0000ffffL
+#endif
+
+#define LDSEM_UNLOCKED		0L
+#define LDSEM_ACTIVE_BIAS	1L
+#define LDSEM_WAIT_BIAS		(-LDSEM_ACTIVE_MASK-1)
+#define LDSEM_READ_BIAS		LDSEM_ACTIVE_BIAS
+#define LDSEM_WRITE_BIAS	(LDSEM_WAIT_BIAS + LDSEM_ACTIVE_BIAS)
+
+struct ldsem_waiter {
+	struct list_head list;
+	struct task_struct *task;
+};
+
+/*
+ * Initialize an ldsem:
+ */
+void __init_ldsem(struct ld_semaphore *sem, const char *name,
+		  struct lock_class_key *key)
+{
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	/*
+	 * Make sure we are not reinitializing a held semaphore:
+	 */
+	debug_check_no_locks_freed((void *)sem, sizeof(*sem));
+	lockdep_init_map(&sem->dep_map, name, key, 0);
+#endif
+	atomic_long_set(&sem->count, LDSEM_UNLOCKED);
+	sem->wait_readers = 0;
+	raw_spin_lock_init(&sem->wait_lock);
+	INIT_LIST_HEAD(&sem->read_wait);
+	INIT_LIST_HEAD(&sem->write_wait);
+}
+
+static void __ldsem_wake_readers(struct ld_semaphore *sem)
+{
+	struct ldsem_waiter *waiter, *next;
+	struct task_struct *tsk;
+	long adjust, count;
+
+	/*
+	 * Try to grant read locks to all readers on the read wait list.
+	 * Note the 'active part' of the count is incremented by
+	 * the number of readers before waking any processes up.
+	 */
+	adjust = sem->wait_readers * (LDSEM_ACTIVE_BIAS - LDSEM_WAIT_BIAS);
+	count = atomic_long_add_return(adjust, &sem->count);
+	do {
+		if (count > 0)
+			break;
+		if (atomic_long_try_cmpxchg(&sem->count, &count, count - adjust))
+			return;
+	} while (1);
+
+	list_for_each_entry_safe(waiter, next, &sem->read_wait, list) {
+		tsk = waiter->task;
+		smp_store_release(&waiter->task, NULL);
+		wake_up_process(tsk);
+		put_task_struct(tsk);
+	}
+	INIT_LIST_HEAD(&sem->read_wait);
+	sem->wait_readers = 0;
+}
+
+static inline int writer_trylock(struct ld_semaphore *sem)
+{
+	/*
+	 * Only wake this writer if the active part of the count can be
+	 * transitioned from 0 -> 1
+	 */
+	long count = atomic_long_add_return(LDSEM_ACTIVE_BIAS, &sem->count);
+	do {
+		if ((count & LDSEM_ACTIVE_MASK) == LDSEM_ACTIVE_BIAS)
+			return 1;
+		if (atomic_long_try_cmpxchg(&sem->count, &count, count - LDSEM_ACTIVE_BIAS))
+			return 0;
+	} while (1);
+}
+
+static void __ldsem_wake_writer(struct ld_semaphore *sem)
+{
+	struct ldsem_waiter *waiter;
+
+	waiter = list_entry(sem->write_wait.next, struct ldsem_waiter, list);
+	wake_up_process(waiter->task);
+}
+
+/*
+ * handle the lock release when processes blocked on it that can now run
+ * - if we come here from up_xxxx(), then:
+ *   - the 'active part' of count (&0x0000ffff) reached 0 (but may have changed)
+ *   - the 'waiting part' of count (&0xffff0000) is -ve (and will still be so)
+ * - the spinlock must be held by the caller
+ * - woken process blocks are discarded from the list after having task zeroed
+ */
+static void __ldsem_wake(struct ld_semaphore *sem)
+{
+	if (!list_empty(&sem->write_wait))
+		__ldsem_wake_writer(sem);
+	else if (!list_empty(&sem->read_wait))
+		__ldsem_wake_readers(sem);
+}
+
+static void ldsem_wake(struct ld_semaphore *sem)
+{
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&sem->wait_lock, flags);
+	__ldsem_wake(sem);
+	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
+}
+
+/*
+ * wait for the read lock to be granted
+ */
+static struct ld_semaphore __sched *
+down_read_failed(struct ld_semaphore *sem, long count, long timeout)
+{
+	struct ldsem_waiter waiter;
+	long adjust = -LDSEM_ACTIVE_BIAS + LDSEM_WAIT_BIAS;
+
+	/* set up my own style of waitqueue */
+	raw_spin_lock_irq(&sem->wait_lock);
+
+	/*
+	 * Try to reverse the lock attempt but if the count has changed
+	 * so that reversing fails, check if there are no waiters,
+	 * and early-out if not
+	 */
+	do {
+		if (atomic_long_try_cmpxchg(&sem->count, &count, count + adjust)) {
+			count += adjust;
+			break;
+		}
+		if (count > 0) {
+			raw_spin_unlock_irq(&sem->wait_lock);
+			return sem;
+		}
+	} while (1);
+
+	list_add_tail(&waiter.list, &sem->read_wait);
+	sem->wait_readers++;
+
+	waiter.task = current;
+	get_task_struct(current);
+
+	/* if there are no active locks, wake the new lock owner(s) */
+	if ((count & LDSEM_ACTIVE_MASK) == 0)
+		__ldsem_wake(sem);
+
+	raw_spin_unlock_irq(&sem->wait_lock);
+
+	/* wait to be given the lock */
+	for (;;) {
+		set_current_state(TASK_UNINTERRUPTIBLE);
+
+		if (!smp_load_acquire(&waiter.task))
+			break;
+		if (!timeout)
+			break;
+		timeout = schedule_timeout(timeout);
+	}
+
+	__set_current_state(TASK_RUNNING);
+
+	if (!timeout) {
+		/*
+		 * Lock timed out but check if this task was just
+		 * granted lock ownership - if so, pretend there
+		 * was no timeout; otherwise, cleanup lock wait.
+		 */
+		raw_spin_lock_irq(&sem->wait_lock);
+		if (waiter.task) {
+			atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count);
+			sem->wait_readers--;
+			list_del(&waiter.list);
+			raw_spin_unlock_irq(&sem->wait_lock);
+			put_task_struct(waiter.task);
+			return NULL;
+		}
+		raw_spin_unlock_irq(&sem->wait_lock);
+	}
+
+	return sem;
+}
+
+/*
+ * wait for the write lock to be granted
+ */
+static struct ld_semaphore __sched *
+down_write_failed(struct ld_semaphore *sem, long count, long timeout)
+{
+	struct ldsem_waiter waiter;
+	long adjust = -LDSEM_ACTIVE_BIAS;
+	int locked = 0;
+
+	/* set up my own style of waitqueue */
+	raw_spin_lock_irq(&sem->wait_lock);
+
+	/*
+	 * Try to reverse the lock attempt but if the count has changed
+	 * so that reversing fails, check if the lock is now owned,
+	 * and early-out if so.
+	 */
+	do {
+		if (atomic_long_try_cmpxchg(&sem->count, &count, count + adjust))
+			break;
+		if ((count & LDSEM_ACTIVE_MASK) == LDSEM_ACTIVE_BIAS) {
+			raw_spin_unlock_irq(&sem->wait_lock);
+			return sem;
+		}
+	} while (1);
+
+	list_add_tail(&waiter.list, &sem->write_wait);
+
+	waiter.task = current;
+
+	set_current_state(TASK_UNINTERRUPTIBLE);
+	for (;;) {
+		if (!timeout)
+			break;
+		raw_spin_unlock_irq(&sem->wait_lock);
+		timeout = schedule_timeout(timeout);
+		raw_spin_lock_irq(&sem->wait_lock);
+		set_current_state(TASK_UNINTERRUPTIBLE);
+		locked = writer_trylock(sem);
+		if (locked)
+			break;
+	}
+
+	if (!locked)
+		atomic_long_add_return(-LDSEM_WAIT_BIAS, &sem->count);
+	list_del(&waiter.list);
+
+	/*
+	 * In case of timeout, wake up every reader who gave the right of way
+	 * to writer. Prevent separation readers into two groups:
+	 * one that helds semaphore and another that sleeps.
+	 * (in case of no contention with a writer)
+	 */
+	if (!locked && list_empty(&sem->write_wait))
+		__ldsem_wake_readers(sem);
+
+	raw_spin_unlock_irq(&sem->wait_lock);
+
+	__set_current_state(TASK_RUNNING);
+
+	/* lock wait may have timed out */
+	if (!locked)
+		return NULL;
+	return sem;
+}
+
+
+
+static int __ldsem_down_read_nested(struct ld_semaphore *sem,
+					   int subclass, long timeout)
+{
+	long count;
+
+	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
+
+	count = atomic_long_add_return(LDSEM_READ_BIAS, &sem->count);
+	if (count <= 0) {
+		lock_contended(&sem->dep_map, _RET_IP_);
+		if (!down_read_failed(sem, count, timeout)) {
+			rwsem_release(&sem->dep_map, _RET_IP_);
+			return 0;
+		}
+	}
+	lock_acquired(&sem->dep_map, _RET_IP_);
+	return 1;
+}
+
+static int __ldsem_down_write_nested(struct ld_semaphore *sem,
+					    int subclass, long timeout)
+{
+	long count;
+
+	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
+
+	count = atomic_long_add_return(LDSEM_WRITE_BIAS, &sem->count);
+	if ((count & LDSEM_ACTIVE_MASK) != LDSEM_ACTIVE_BIAS) {
+		lock_contended(&sem->dep_map, _RET_IP_);
+		if (!down_write_failed(sem, count, timeout)) {
+			rwsem_release(&sem->dep_map, _RET_IP_);
+			return 0;
+		}
+	}
+	lock_acquired(&sem->dep_map, _RET_IP_);
+	return 1;
+}
+
+
+/*
+ * lock for reading -- returns 1 if successful, 0 if timed out
+ */
+int __sched ldsem_down_read(struct ld_semaphore *sem, long timeout)
+{
+	might_sleep();
+	return __ldsem_down_read_nested(sem, 0, timeout);
+}
+
+/*
+ * trylock for reading -- returns 1 if successful, 0 if contention
+ */
+int ldsem_down_read_trylock(struct ld_semaphore *sem)
+{
+	long count = atomic_long_read(&sem->count);
+
+	while (count >= 0) {
+		if (atomic_long_try_cmpxchg(&sem->count, &count, count + LDSEM_READ_BIAS)) {
+			rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
+			lock_acquired(&sem->dep_map, _RET_IP_);
+			return 1;
+		}
+	}
+	return 0;
+}
+
+/*
+ * lock for writing -- returns 1 if successful, 0 if timed out
+ */
+int __sched ldsem_down_write(struct ld_semaphore *sem, long timeout)
+{
+	might_sleep();
+	return __ldsem_down_write_nested(sem, 0, timeout);
+}
+
+/*
+ * release a read lock
+ */
+void ldsem_up_read(struct ld_semaphore *sem)
+{
+	long count;
+
+	rwsem_release(&sem->dep_map, _RET_IP_);
+
+	count = atomic_long_add_return(-LDSEM_READ_BIAS, &sem->count);
+	if (count < 0 && (count & LDSEM_ACTIVE_MASK) == 0)
+		ldsem_wake(sem);
+}
+
+/*
+ * release a write lock
+ */
+void ldsem_up_write(struct ld_semaphore *sem)
+{
+	long count;
+
+	rwsem_release(&sem->dep_map, _RET_IP_);
+
+	count = atomic_long_add_return(-LDSEM_WRITE_BIAS, &sem->count);
+	if (count < 0)
+		ldsem_wake(sem);
+}
+
+
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+
+int ldsem_down_read_nested(struct ld_semaphore *sem, int subclass, long timeout)
+{
+	might_sleep();
+	return __ldsem_down_read_nested(sem, subclass, timeout);
+}
+
+int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
+			    long timeout)
+{
+	might_sleep();
+	return __ldsem_down_write_nested(sem, subclass, timeout);
+}
+
+#endif