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, 224 insertions, 0 deletions

diff --git a/lib/tests/kfifo_kunit.c b/lib/tests/kfifo_kunit.c
new file mode 100644
index 000000000..a85eedc31
--- /dev/null
+++ b/lib/tests/kfifo_kunit.c
@@ -0,0 +1,224 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit test for the generic kernel FIFO implementation.
+ *
+ * Copyright (C) 2024 Diego Vieira <diego.daniel.professional@gmail.com>
+ */
+#include <kunit/test.h>
+
+#include <linux/kfifo.h>
+
+#define KFIFO_SIZE 32
+#define N_ELEMENTS 5
+
+static void kfifo_test_reset_should_clear_the_fifo(struct kunit *test)
+{
+	DEFINE_KFIFO(my_fifo, u8, KFIFO_SIZE);
+
+	kfifo_put(&my_fifo, 1);
+	kfifo_put(&my_fifo, 2);
+	kfifo_put(&my_fifo, 3);
+	KUNIT_EXPECT_EQ(test, kfifo_len(&my_fifo), 3);
+
+	kfifo_reset(&my_fifo);
+
+	KUNIT_EXPECT_EQ(test, kfifo_len(&my_fifo), 0);
+	KUNIT_EXPECT_TRUE(test, kfifo_is_empty(&my_fifo));
+}
+
+static void kfifo_test_define_should_define_an_empty_fifo(struct kunit *test)
+{
+	DEFINE_KFIFO(my_fifo, u8, KFIFO_SIZE);
+
+	KUNIT_EXPECT_TRUE(test, kfifo_initialized(&my_fifo));
+	KUNIT_EXPECT_TRUE(test, kfifo_is_empty(&my_fifo));
+	KUNIT_EXPECT_EQ(test, kfifo_len(&my_fifo), 0);
+}
+
+static void kfifo_test_len_should_ret_n_of_stored_elements(struct kunit *test)
+{
+	u8 buffer1[N_ELEMENTS];
+
+	for (int i = 0; i < N_ELEMENTS; i++)
+		buffer1[i] = i + 1;
+
+	DEFINE_KFIFO(my_fifo, u8, KFIFO_SIZE);
+
+	KUNIT_EXPECT_EQ(test, kfifo_len(&my_fifo), 0);
+
+	kfifo_in(&my_fifo, buffer1, N_ELEMENTS);
+	KUNIT_EXPECT_EQ(test, kfifo_len(&my_fifo), N_ELEMENTS);
+
+	kfifo_in(&my_fifo, buffer1, N_ELEMENTS);
+	KUNIT_EXPECT_EQ(test, kfifo_len(&my_fifo), N_ELEMENTS * 2);
+
+	kfifo_reset(&my_fifo);
+	KUNIT_EXPECT_EQ(test, kfifo_len(&my_fifo), 0);
+}
+
+static void kfifo_test_put_should_insert_and_get_should_pop(struct kunit *test)
+{
+	u8 out_data = 0;
+	int processed_elements;
+	u8 elements[] = { 3, 5, 11 };
+
+	DEFINE_KFIFO(my_fifo, u8, KFIFO_SIZE);
+
+	// If the fifo is empty, get returns 0
+	processed_elements = kfifo_get(&my_fifo, &out_data);
+	KUNIT_EXPECT_EQ(test, processed_elements, 0);
+	KUNIT_EXPECT_EQ(test, out_data, 0);
+
+	for (int i = 0; i < 3; i++)
+		kfifo_put(&my_fifo, elements[i]);
+
+	for (int i = 0; i < 3; i++) {
+		processed_elements = kfifo_get(&my_fifo, &out_data);
+		KUNIT_EXPECT_EQ(test, processed_elements, 1);
+		KUNIT_EXPECT_EQ(test, out_data, elements[i]);
+	}
+}
+
+static void kfifo_test_in_should_insert_multiple_elements(struct kunit *test)
+{
+	u8 in_buffer[] = { 11, 25, 65 };
+	u8 out_data;
+	int processed_elements;
+
+	DEFINE_KFIFO(my_fifo, u8, KFIFO_SIZE);
+
+	kfifo_in(&my_fifo, in_buffer, 3);
+
+	for (int i = 0; i < 3; i++) {
+		processed_elements = kfifo_get(&my_fifo, &out_data);
+		KUNIT_EXPECT_EQ(test, processed_elements, 1);
+		KUNIT_EXPECT_EQ(test, out_data, in_buffer[i]);
+	}
+}
+
+static void kfifo_test_out_should_pop_multiple_elements(struct kunit *test)
+{
+	u8 in_buffer[] = { 11, 25, 65 };
+	u8 out_buffer[3];
+	int copied_elements;
+
+	DEFINE_KFIFO(my_fifo, u8, KFIFO_SIZE);
+
+	for (int i = 0; i < 3; i++)
+		kfifo_put(&my_fifo, in_buffer[i]);
+
+	copied_elements = kfifo_out(&my_fifo, out_buffer, 3);
+	KUNIT_EXPECT_EQ(test, copied_elements, 3);
+
+	for (int i = 0; i < 3; i++)
+		KUNIT_EXPECT_EQ(test, out_buffer[i], in_buffer[i]);
+	KUNIT_EXPECT_TRUE(test, kfifo_is_empty(&my_fifo));
+}
+
+static void kfifo_test_dec_init_should_define_an_empty_fifo(struct kunit *test)
+{
+	DECLARE_KFIFO(my_fifo, u8, KFIFO_SIZE);
+
+	INIT_KFIFO(my_fifo);
+
+	// my_fifo is a struct with an inplace buffer
+	KUNIT_EXPECT_FALSE(test, __is_kfifo_ptr(&my_fifo));
+
+	KUNIT_EXPECT_TRUE(test, kfifo_initialized(&my_fifo));
+}
+
+static void kfifo_test_define_should_equal_declare_init(struct kunit *test)
+{
+	// declare a variable my_fifo of type struct kfifo of u8
+	DECLARE_KFIFO(my_fifo1, u8, KFIFO_SIZE);
+	// initialize the my_fifo variable
+	INIT_KFIFO(my_fifo1);
+
+	// DEFINE_KFIFO declares the variable with the initial value
+	// essentially the same as calling DECLARE_KFIFO and INIT_KFIFO
+	DEFINE_KFIFO(my_fifo2, u8, KFIFO_SIZE);
+
+	// my_fifo1 and my_fifo2 have the same size
+	KUNIT_EXPECT_EQ(test, sizeof(my_fifo1), sizeof(my_fifo2));
+	KUNIT_EXPECT_EQ(test, kfifo_initialized(&my_fifo1),
+			kfifo_initialized(&my_fifo2));
+	KUNIT_EXPECT_EQ(test, kfifo_is_empty(&my_fifo1),
+			kfifo_is_empty(&my_fifo2));
+}
+
+static void kfifo_test_alloc_should_initiliaze_a_ptr_fifo(struct kunit *test)
+{
+	int ret;
+	DECLARE_KFIFO_PTR(my_fifo, u8);
+
+	INIT_KFIFO(my_fifo);
+
+	// kfifo_initialized returns false signaling the buffer pointer is NULL
+	KUNIT_EXPECT_FALSE(test, kfifo_initialized(&my_fifo));
+
+	// kfifo_alloc allocates the buffer
+	ret = kfifo_alloc(&my_fifo, KFIFO_SIZE, GFP_KERNEL);
+	KUNIT_EXPECT_EQ_MSG(test, ret, 0, "Memory allocation should succeed");
+	KUNIT_EXPECT_TRUE(test, kfifo_initialized(&my_fifo));
+
+	// kfifo_free frees the buffer
+	kfifo_free(&my_fifo);
+}
+
+static void kfifo_test_peek_should_not_remove_elements(struct kunit *test)
+{
+	u8 out_data;
+	int processed_elements;
+
+	DEFINE_KFIFO(my_fifo, u8, KFIFO_SIZE);
+
+	// If the fifo is empty, peek returns 0
+	processed_elements = kfifo_peek(&my_fifo, &out_data);
+	KUNIT_EXPECT_EQ(test, processed_elements, 0);
+
+	kfifo_put(&my_fifo, 3);
+	kfifo_put(&my_fifo, 5);
+	kfifo_put(&my_fifo, 11);
+
+	KUNIT_EXPECT_EQ(test, kfifo_len(&my_fifo), 3);
+
+	processed_elements = kfifo_peek(&my_fifo, &out_data);
+	KUNIT_EXPECT_EQ(test, processed_elements, 1);
+	KUNIT_EXPECT_EQ(test, out_data, 3);
+
+	KUNIT_EXPECT_EQ(test, kfifo_len(&my_fifo), 3);
+
+	// Using peek doesn't remove the element
+	// so the read element and the fifo length
+	// remains the same
+	processed_elements = kfifo_peek(&my_fifo, &out_data);
+	KUNIT_EXPECT_EQ(test, processed_elements, 1);
+	KUNIT_EXPECT_EQ(test, out_data, 3);
+
+	KUNIT_EXPECT_EQ(test, kfifo_len(&my_fifo), 3);
+}
+
+static struct kunit_case kfifo_test_cases[] = {
+	KUNIT_CASE(kfifo_test_reset_should_clear_the_fifo),
+	KUNIT_CASE(kfifo_test_define_should_define_an_empty_fifo),
+	KUNIT_CASE(kfifo_test_len_should_ret_n_of_stored_elements),
+	KUNIT_CASE(kfifo_test_put_should_insert_and_get_should_pop),
+	KUNIT_CASE(kfifo_test_in_should_insert_multiple_elements),
+	KUNIT_CASE(kfifo_test_out_should_pop_multiple_elements),
+	KUNIT_CASE(kfifo_test_dec_init_should_define_an_empty_fifo),
+	KUNIT_CASE(kfifo_test_define_should_equal_declare_init),
+	KUNIT_CASE(kfifo_test_alloc_should_initiliaze_a_ptr_fifo),
+	KUNIT_CASE(kfifo_test_peek_should_not_remove_elements),
+	{},
+};
+
+static struct kunit_suite kfifo_test_module = {
+	.name = "kfifo",
+	.test_cases = kfifo_test_cases,
+};
+
+kunit_test_suites(&kfifo_test_module);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Diego Vieira <diego.daniel.professional@gmail.com>");
+MODULE_DESCRIPTION("KUnit test for the kernel FIFO");