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, 122 insertions, 0 deletions

diff --git a/drivers/firewire/ohci-serdes-test.c b/drivers/firewire/ohci-serdes-test.c
new file mode 100644
index 000000000..258f66861
--- /dev/null
+++ b/drivers/firewire/ohci-serdes-test.c
@@ -0,0 +1,122 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+//
+// ohci-serdes-test.c - An application of Kunit to check serialization/deserialization of data in
+//			buffers and registers defined in 1394 OHCI specification.
+//
+// Copyright (c) 2024 Takashi Sakamoto
+
+#include <kunit/test.h>
+
+#include "ohci.h"
+
+
+static void test_self_id_count_register_deserialization(struct kunit *test)
+{
+	const u32 expected = 0x803d0594;
+
+	bool is_error = ohci1394_self_id_count_is_error(expected);
+	u8 generation = ohci1394_self_id_count_get_generation(expected);
+	u32 size = ohci1394_self_id_count_get_size(expected);
+
+	KUNIT_EXPECT_TRUE(test, is_error);
+	KUNIT_EXPECT_EQ(test, 0x3d, generation);
+	KUNIT_EXPECT_EQ(test, 0x165, size);
+}
+
+static void test_self_id_receive_buffer_deserialization(struct kunit *test)
+{
+	const u32 buffer[] = {
+		0x0006f38b,
+		0x807fcc56,
+		0x7f8033a9,
+		0x8145cc5e,
+		0x7eba33a1,
+	};
+
+	u8 generation = ohci1394_self_id_receive_q0_get_generation(buffer[0]);
+	u16 timestamp = ohci1394_self_id_receive_q0_get_timestamp(buffer[0]);
+
+	KUNIT_EXPECT_EQ(test, 0x6, generation);
+	KUNIT_EXPECT_EQ(test, 0xf38b, timestamp);
+}
+
+static void test_at_data_serdes(struct kunit *test)
+{
+	static const __le32 expected[] = {
+		cpu_to_le32(0x00020e80),
+		cpu_to_le32(0xffc2ffff),
+		cpu_to_le32(0xe0000000),
+	};
+	__le32 quadlets[] = {0, 0, 0};
+	bool has_src_bus_id = ohci1394_at_data_get_src_bus_id(expected);
+	unsigned int speed = ohci1394_at_data_get_speed(expected);
+	unsigned int tlabel = ohci1394_at_data_get_tlabel(expected);
+	unsigned int retry = ohci1394_at_data_get_retry(expected);
+	unsigned int tcode = ohci1394_at_data_get_tcode(expected);
+	unsigned int destination_id = ohci1394_at_data_get_destination_id(expected);
+	u64 destination_offset = ohci1394_at_data_get_destination_offset(expected);
+
+	KUNIT_EXPECT_FALSE(test, has_src_bus_id);
+	KUNIT_EXPECT_EQ(test, 0x02, speed);
+	KUNIT_EXPECT_EQ(test, 0x03, tlabel);
+	KUNIT_EXPECT_EQ(test, 0x02, retry);
+	KUNIT_EXPECT_EQ(test, 0x08, tcode);
+
+	ohci1394_at_data_set_src_bus_id(quadlets, has_src_bus_id);
+	ohci1394_at_data_set_speed(quadlets, speed);
+	ohci1394_at_data_set_tlabel(quadlets, tlabel);
+	ohci1394_at_data_set_retry(quadlets, retry);
+	ohci1394_at_data_set_tcode(quadlets, tcode);
+	ohci1394_at_data_set_destination_id(quadlets, destination_id);
+	ohci1394_at_data_set_destination_offset(quadlets, destination_offset);
+
+	KUNIT_EXPECT_MEMEQ(test, quadlets, expected, sizeof(expected));
+}
+
+static void test_it_data_serdes(struct kunit *test)
+{
+	static const __le32 expected[] = {
+		cpu_to_le32(0x000349a7),
+		cpu_to_le32(0x02300000),
+	};
+	__le32 quadlets[] = {0, 0};
+	unsigned int scode = ohci1394_it_data_get_speed(expected);
+	unsigned int tag = ohci1394_it_data_get_tag(expected);
+	unsigned int channel = ohci1394_it_data_get_channel(expected);
+	unsigned int tcode = ohci1394_it_data_get_tcode(expected);
+	unsigned int sync = ohci1394_it_data_get_sync(expected);
+	unsigned int data_length = ohci1394_it_data_get_data_length(expected);
+
+	KUNIT_EXPECT_EQ(test, 0x03, scode);
+	KUNIT_EXPECT_EQ(test, 0x01, tag);
+	KUNIT_EXPECT_EQ(test, 0x09, channel);
+	KUNIT_EXPECT_EQ(test, 0x0a, tcode);
+	KUNIT_EXPECT_EQ(test, 0x7, sync);
+	KUNIT_EXPECT_EQ(test, 0x0230, data_length);
+
+	ohci1394_it_data_set_speed(quadlets, scode);
+	ohci1394_it_data_set_tag(quadlets, tag);
+	ohci1394_it_data_set_channel(quadlets, channel);
+	ohci1394_it_data_set_tcode(quadlets, tcode);
+	ohci1394_it_data_set_sync(quadlets, sync);
+	ohci1394_it_data_set_data_length(quadlets, data_length);
+
+	KUNIT_EXPECT_MEMEQ(test, quadlets, expected, sizeof(expected));
+}
+
+static struct kunit_case ohci_serdes_test_cases[] = {
+	KUNIT_CASE(test_self_id_count_register_deserialization),
+	KUNIT_CASE(test_self_id_receive_buffer_deserialization),
+	KUNIT_CASE(test_at_data_serdes),
+	KUNIT_CASE(test_it_data_serdes),
+	{}
+};
+
+static struct kunit_suite ohci_serdes_test_suite = {
+	.name = "firewire-ohci-serdes",
+	.test_cases = ohci_serdes_test_cases,
+};
+kunit_test_suite(ohci_serdes_test_suite);
+
+MODULE_DESCRIPTION("FireWire buffers and registers serialization/deserialization unit test suite");
+MODULE_LICENSE("GPL");