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, 318 insertions, 0 deletions

diff --git a/lib/tests/hashtable_test.c b/lib/tests/hashtable_test.c
new file mode 100644
index 000000000..3521de6ba
--- /dev/null
+++ b/lib/tests/hashtable_test.c
@@ -0,0 +1,318 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit test for the Kernel Hashtable structures.
+ *
+ * Copyright (C) 2022, Google LLC.
+ * Author: Rae Moar <rmoar@google.com>
+ */
+#include <kunit/test.h>
+
+#include <linux/hashtable.h>
+
+struct hashtable_test_entry {
+	int key;
+	int data;
+	struct hlist_node node;
+	int visited;
+};
+
+static void hashtable_test_hash_init(struct kunit *test)
+{
+	/* Test the different ways of initialising a hashtable. */
+	DEFINE_HASHTABLE(hash1, 2);
+	DECLARE_HASHTABLE(hash2, 3);
+
+	/* When using DECLARE_HASHTABLE, must use hash_init to
+	 * initialize the hashtable.
+	 */
+	hash_init(hash2);
+
+	KUNIT_EXPECT_TRUE(test, hash_empty(hash1));
+	KUNIT_EXPECT_TRUE(test, hash_empty(hash2));
+}
+
+static void hashtable_test_hash_empty(struct kunit *test)
+{
+	struct hashtable_test_entry a;
+	DEFINE_HASHTABLE(hash, 1);
+
+	KUNIT_EXPECT_TRUE(test, hash_empty(hash));
+
+	a.key = 1;
+	a.data = 13;
+	hash_add(hash, &a.node, a.key);
+
+	/* Hashtable should no longer be empty. */
+	KUNIT_EXPECT_FALSE(test, hash_empty(hash));
+}
+
+static void hashtable_test_hash_hashed(struct kunit *test)
+{
+	struct hashtable_test_entry a, b;
+	DEFINE_HASHTABLE(hash, 4);
+
+	a.key = 1;
+	a.data = 13;
+	hash_add(hash, &a.node, a.key);
+	b.key = 1;
+	b.data = 2;
+	hash_add(hash, &b.node, b.key);
+
+	KUNIT_EXPECT_TRUE(test, hash_hashed(&a.node));
+	KUNIT_EXPECT_TRUE(test, hash_hashed(&b.node));
+}
+
+static void hashtable_test_hash_add(struct kunit *test)
+{
+	struct hashtable_test_entry a, b, *x;
+	int bkt;
+	DEFINE_HASHTABLE(hash, 3);
+
+	a.key = 1;
+	a.data = 13;
+	a.visited = 0;
+	hash_add(hash, &a.node, a.key);
+	b.key = 2;
+	b.data = 10;
+	b.visited = 0;
+	hash_add(hash, &b.node, b.key);
+
+	hash_for_each(hash, bkt, x, node) {
+		x->visited++;
+		if (x->key == a.key)
+			KUNIT_EXPECT_EQ(test, x->data, 13);
+		else if (x->key == b.key)
+			KUNIT_EXPECT_EQ(test, x->data, 10);
+		else
+			KUNIT_FAIL(test, "Unexpected key in hashtable.");
+	}
+
+	/* Both entries should have been visited exactly once. */
+	KUNIT_EXPECT_EQ(test, a.visited, 1);
+	KUNIT_EXPECT_EQ(test, b.visited, 1);
+}
+
+static void hashtable_test_hash_del(struct kunit *test)
+{
+	struct hashtable_test_entry a, b, *x;
+	DEFINE_HASHTABLE(hash, 6);
+
+	a.key = 1;
+	a.data = 13;
+	hash_add(hash, &a.node, a.key);
+	b.key = 2;
+	b.data = 10;
+	b.visited = 0;
+	hash_add(hash, &b.node, b.key);
+
+	hash_del(&b.node);
+	hash_for_each_possible(hash, x, node, b.key) {
+		x->visited++;
+		KUNIT_EXPECT_NE(test, x->key, b.key);
+	}
+
+	/* The deleted entry should not have been visited. */
+	KUNIT_EXPECT_EQ(test, b.visited, 0);
+
+	hash_del(&a.node);
+
+	/* The hashtable should be empty. */
+	KUNIT_EXPECT_TRUE(test, hash_empty(hash));
+}
+
+static void hashtable_test_hash_for_each(struct kunit *test)
+{
+	struct hashtable_test_entry entries[3];
+	struct hashtable_test_entry *x;
+	int bkt, i, j, count;
+	DEFINE_HASHTABLE(hash, 3);
+
+	/* Add three entries to the hashtable. */
+	for (i = 0; i < 3; i++) {
+		entries[i].key = i;
+		entries[i].data = i + 10;
+		entries[i].visited = 0;
+		hash_add(hash, &entries[i].node, entries[i].key);
+	}
+
+	count = 0;
+	hash_for_each(hash, bkt, x, node) {
+		x->visited += 1;
+		KUNIT_ASSERT_GE_MSG(test, x->key, 0, "Unexpected key in hashtable.");
+		KUNIT_ASSERT_LT_MSG(test, x->key, 3, "Unexpected key in hashtable.");
+		count++;
+	}
+
+	/* Should have visited each entry exactly once. */
+	KUNIT_EXPECT_EQ(test, count, 3);
+	for (j = 0; j < 3; j++)
+		KUNIT_EXPECT_EQ(test, entries[j].visited, 1);
+}
+
+static void hashtable_test_hash_for_each_safe(struct kunit *test)
+{
+	struct hashtable_test_entry entries[3];
+	struct hashtable_test_entry *x;
+	struct hlist_node *tmp;
+	int bkt, i, j, count;
+	DEFINE_HASHTABLE(hash, 3);
+
+	/* Add three entries to the hashtable. */
+	for (i = 0; i < 3; i++) {
+		entries[i].key = i;
+		entries[i].data = i + 10;
+		entries[i].visited = 0;
+		hash_add(hash, &entries[i].node, entries[i].key);
+	}
+
+	count = 0;
+	hash_for_each_safe(hash, bkt, tmp, x, node) {
+		x->visited += 1;
+		KUNIT_ASSERT_GE_MSG(test, x->key, 0, "Unexpected key in hashtable.");
+		KUNIT_ASSERT_LT_MSG(test, x->key, 3, "Unexpected key in hashtable.");
+		count++;
+
+		/* Delete entry during loop. */
+		hash_del(&x->node);
+	}
+
+	/* Should have visited each entry exactly once. */
+	KUNIT_EXPECT_EQ(test, count, 3);
+	for (j = 0; j < 3; j++)
+		KUNIT_EXPECT_EQ(test, entries[j].visited, 1);
+}
+
+static void hashtable_test_hash_for_each_possible(struct kunit *test)
+{
+	struct hashtable_test_entry entries[4];
+	struct hashtable_test_entry *x, *y;
+	int buckets[2];
+	int bkt, i, j, count;
+	DEFINE_HASHTABLE(hash, 5);
+
+	/* Add three entries with key = 0 to the hashtable. */
+	for (i = 0; i < 3; i++) {
+		entries[i].key = 0;
+		entries[i].data = i;
+		entries[i].visited = 0;
+		hash_add(hash, &entries[i].node, entries[i].key);
+	}
+
+	/* Add an entry with key = 1. */
+	entries[3].key = 1;
+	entries[3].data = 3;
+	entries[3].visited = 0;
+	hash_add(hash, &entries[3].node, entries[3].key);
+
+	count = 0;
+	hash_for_each_possible(hash, x, node, 0) {
+		x->visited += 1;
+		KUNIT_ASSERT_GE_MSG(test, x->data, 0, "Unexpected data in hashtable.");
+		KUNIT_ASSERT_LT_MSG(test, x->data, 4, "Unexpected data in hashtable.");
+		count++;
+	}
+
+	/* Should have visited each entry with key = 0 exactly once. */
+	for (j = 0; j < 3; j++)
+		KUNIT_EXPECT_EQ(test, entries[j].visited, 1);
+
+	/* Save the buckets for the different keys. */
+	hash_for_each(hash, bkt, y, node) {
+		KUNIT_ASSERT_GE_MSG(test, y->key, 0, "Unexpected key in hashtable.");
+		KUNIT_ASSERT_LE_MSG(test, y->key, 1, "Unexpected key in hashtable.");
+		buckets[y->key] = bkt;
+	}
+
+	/* If entry with key = 1 is in the same bucket as the entries with
+	 * key = 0, check it was visited. Otherwise ensure that only three
+	 * entries were visited.
+	 */
+	if (buckets[0] == buckets[1]) {
+		KUNIT_EXPECT_EQ(test, count, 4);
+		KUNIT_EXPECT_EQ(test, entries[3].visited, 1);
+	} else {
+		KUNIT_EXPECT_EQ(test, count, 3);
+		KUNIT_EXPECT_EQ(test, entries[3].visited, 0);
+	}
+}
+
+static void hashtable_test_hash_for_each_possible_safe(struct kunit *test)
+{
+	struct hashtable_test_entry entries[4];
+	struct hashtable_test_entry *x, *y;
+	struct hlist_node *tmp;
+	int buckets[2];
+	int bkt, i, j, count;
+	DEFINE_HASHTABLE(hash, 5);
+
+	/* Add three entries with key = 0 to the hashtable. */
+	for (i = 0; i < 3; i++) {
+		entries[i].key = 0;
+		entries[i].data = i;
+		entries[i].visited = 0;
+		hash_add(hash, &entries[i].node, entries[i].key);
+	}
+
+	/* Add an entry with key = 1. */
+	entries[3].key = 1;
+	entries[3].data = 3;
+	entries[3].visited = 0;
+	hash_add(hash, &entries[3].node, entries[3].key);
+
+	count = 0;
+	hash_for_each_possible_safe(hash, x, tmp, node, 0) {
+		x->visited += 1;
+		KUNIT_ASSERT_GE_MSG(test, x->data, 0, "Unexpected data in hashtable.");
+		KUNIT_ASSERT_LT_MSG(test, x->data, 4, "Unexpected data in hashtable.");
+		count++;
+
+		/* Delete entry during loop. */
+		hash_del(&x->node);
+	}
+
+	/* Should have visited each entry with key = 0 exactly once. */
+	for (j = 0; j < 3; j++)
+		KUNIT_EXPECT_EQ(test, entries[j].visited, 1);
+
+	/* Save the buckets for the different keys. */
+	hash_for_each(hash, bkt, y, node) {
+		KUNIT_ASSERT_GE_MSG(test, y->key, 0, "Unexpected key in hashtable.");
+		KUNIT_ASSERT_LE_MSG(test, y->key, 1, "Unexpected key in hashtable.");
+		buckets[y->key] = bkt;
+	}
+
+	/* If entry with key = 1 is in the same bucket as the entries with
+	 * key = 0, check it was visited. Otherwise ensure that only three
+	 * entries were visited.
+	 */
+	if (buckets[0] == buckets[1]) {
+		KUNIT_EXPECT_EQ(test, count, 4);
+		KUNIT_EXPECT_EQ(test, entries[3].visited, 1);
+	} else {
+		KUNIT_EXPECT_EQ(test, count, 3);
+		KUNIT_EXPECT_EQ(test, entries[3].visited, 0);
+	}
+}
+
+static struct kunit_case hashtable_test_cases[] = {
+	KUNIT_CASE(hashtable_test_hash_init),
+	KUNIT_CASE(hashtable_test_hash_empty),
+	KUNIT_CASE(hashtable_test_hash_hashed),
+	KUNIT_CASE(hashtable_test_hash_add),
+	KUNIT_CASE(hashtable_test_hash_del),
+	KUNIT_CASE(hashtable_test_hash_for_each),
+	KUNIT_CASE(hashtable_test_hash_for_each_safe),
+	KUNIT_CASE(hashtable_test_hash_for_each_possible),
+	KUNIT_CASE(hashtable_test_hash_for_each_possible_safe),
+	{},
+};
+
+static struct kunit_suite hashtable_test_module = {
+	.name = "hashtable",
+	.test_cases = hashtable_test_cases,
+};
+
+kunit_test_suites(&hashtable_test_module);
+
+MODULE_DESCRIPTION("KUnit test for the Kernel Hashtable structures");
+MODULE_LICENSE("GPL");