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, 275 insertions, 0 deletions

diff --git a/lib/tests/cmdline_kunit.c b/lib/tests/cmdline_kunit.c
new file mode 100644
index 000000000..3f61ff8d3
--- /dev/null
+++ b/lib/tests/cmdline_kunit.c
@@ -0,0 +1,275 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Test cases for API provided by cmdline.c
+ */
+
+#include <kunit/test.h>
+#include <linux/kernel.h>
+#include <linux/random.h>
+#include <linux/sizes.h>
+#include <linux/string.h>
+
+static const char *cmdline_test_strings[] = {
+	"\"\"", ""  , "=" , "\"-", ","    , "-,"   , ",-"   , "-" ,
+	"+,"  , "--", ",,", "''" , "\"\",", "\",\"", "-\"\"", "\"",
+};
+
+static const int cmdline_test_values[] = {
+	1, 1, 1, 1, 2, 3, 2, 3,
+	1, 3, 2, 1, 1, 1, 3, 1,
+};
+
+static_assert(ARRAY_SIZE(cmdline_test_strings) == ARRAY_SIZE(cmdline_test_values));
+
+static const char *cmdline_test_range_strings[] = {
+	"-7" , "--7"  , "-1-2"    , "7--9",
+	"7-" , "-7--9", "7-9,"    , "9-7" ,
+	"5-a", "a-5"  , "5-8"     , ",8-5",
+	"+,1", "-,4"  , "-3,0-1,6", "4,-" ,
+	" +2", " -9"  , "0-1,-3,6", "- 9" ,
+};
+
+static const int cmdline_test_range_values[][16] = {
+	{ 1, -7, }, { 0, -0, }, { 4, -1, 0, +1, 2, }, { 0, 7, },
+	{ 0, +7, }, { 0, -7, }, { 3, +7, 8, +9, 0, }, { 0, 9, },
+	{ 0, +5, }, { 0, -0, }, { 4, +5, 6, +7, 8, }, { 0, 0, },
+	{ 0, +0, }, { 0, -0, }, { 4, -3, 0, +1, 6, }, { 1, 4, },
+	{ 0, +0, }, { 0, -0, }, { 4, +0, 1, -3, 6, }, { 0, 0, },
+};
+
+static_assert(ARRAY_SIZE(cmdline_test_range_strings) == ARRAY_SIZE(cmdline_test_range_values));
+
+static void cmdline_do_one_test(struct kunit *test, const char *in, int rc, int offset)
+{
+	const char *fmt = "Pattern: %s";
+	const char *out = in;
+	int dummy;
+	int ret;
+
+	ret = get_option((char **)&out, &dummy);
+
+	KUNIT_EXPECT_EQ_MSG(test, ret, rc, fmt, in);
+	KUNIT_EXPECT_PTR_EQ_MSG(test, out, in + offset, fmt, in);
+}
+
+static void cmdline_test_noint(struct kunit *test)
+{
+	unsigned int i = 0;
+
+	do {
+		const char *str = cmdline_test_strings[i];
+		int rc = 0;
+		int offset;
+
+		/* Only first and leading '-' will advance the pointer */
+		offset = !!(*str == '-');
+		cmdline_do_one_test(test, str, rc, offset);
+	} while (++i < ARRAY_SIZE(cmdline_test_strings));
+}
+
+static void cmdline_test_lead_int(struct kunit *test)
+{
+	unsigned int i = 0;
+	char in[32];
+
+	do {
+		const char *str = cmdline_test_strings[i];
+		int rc = cmdline_test_values[i];
+		int offset;
+
+		sprintf(in, "%u%s", get_random_u8(), str);
+		/* Only first '-' after the number will advance the pointer */
+		offset = strlen(in) - strlen(str) + !!(rc == 2);
+		cmdline_do_one_test(test, in, rc, offset);
+	} while (++i < ARRAY_SIZE(cmdline_test_strings));
+}
+
+static void cmdline_test_tail_int(struct kunit *test)
+{
+	unsigned int i = 0;
+	char in[32];
+
+	do {
+		const char *str = cmdline_test_strings[i];
+		/* When "" or "-" the result will be valid integer */
+		int rc = strcmp(str, "") ? (strcmp(str, "-") ? 0 : 1) : 1;
+		int offset;
+
+		sprintf(in, "%s%u", str, get_random_u8());
+		/*
+		 * Only first and leading '-' not followed by integer
+		 * will advance the pointer.
+		 */
+		offset = rc ? strlen(in) : !!(*str == '-');
+		cmdline_do_one_test(test, in, rc, offset);
+	} while (++i < ARRAY_SIZE(cmdline_test_strings));
+}
+
+static void cmdline_do_one_range_test(struct kunit *test, const char *in,
+				      unsigned int n, const int *e)
+{
+	unsigned int i;
+	int r[16];
+	int *p;
+
+	memset(r, 0, sizeof(r));
+	get_options(in, ARRAY_SIZE(r), r);
+	KUNIT_EXPECT_EQ_MSG(test, r[0], e[0], "in test %u (parsed) expected %d numbers, got %d",
+			    n, e[0], r[0]);
+	for (i = 1; i < ARRAY_SIZE(r); i++)
+		KUNIT_EXPECT_EQ_MSG(test, r[i], e[i], "in test %u at %u", n, i);
+
+	memset(r, 0, sizeof(r));
+	get_options(in, 0, r);
+	KUNIT_EXPECT_EQ_MSG(test, r[0], e[0], "in test %u (validated) expected %d numbers, got %d",
+			    n, e[0], r[0]);
+
+	p = memchr_inv(&r[1], 0, sizeof(r) - sizeof(r[0]));
+	KUNIT_EXPECT_PTR_EQ_MSG(test, p, NULL, "in test %u at %td out of bound", n, p - r);
+}
+
+static void cmdline_test_range(struct kunit *test)
+{
+	unsigned int i = 0;
+
+	do {
+		const char *str = cmdline_test_range_strings[i];
+		const int *e = cmdline_test_range_values[i];
+
+		cmdline_do_one_range_test(test, str, i, e);
+	} while (++i < ARRAY_SIZE(cmdline_test_range_strings));
+}
+
+static void cmdline_test_next_arg_quoted_value(struct kunit *test)
+{
+	char in[] = "foo=\"bar baz\" qux=1";
+	char *next, *param, *val;
+
+	next = next_arg(in, &param, &val);
+	KUNIT_EXPECT_STREQ(test, param, "foo");
+	KUNIT_ASSERT_NOT_NULL(test, val);
+	KUNIT_EXPECT_STREQ(test, val, "bar baz");
+	KUNIT_EXPECT_STREQ(test, next, "qux=1");
+
+	next = next_arg(next, &param, &val);
+	KUNIT_EXPECT_STREQ(test, param, "qux");
+	KUNIT_ASSERT_NOT_NULL(test, val);
+	KUNIT_EXPECT_STREQ(test, val, "1");
+	KUNIT_EXPECT_STREQ(test, next, "");
+}
+
+static void cmdline_test_next_arg_bare_quote_regression(struct kunit *test)
+{
+	char in[] = "foo=bar \"";
+	char *next, *param, *val;
+
+	next = next_arg(in, &param, &val);
+	KUNIT_EXPECT_STREQ(test, param, "foo");
+	KUNIT_ASSERT_NOT_NULL(test, val);
+	KUNIT_EXPECT_STREQ(test, val, "bar");
+	KUNIT_EXPECT_STREQ(test, next, "\"");
+
+	/* This hits the i == 0 quoted-token case fixed by 9847f21225c4. */
+	next = next_arg(next, &param, &val);
+	KUNIT_EXPECT_STREQ(test, param, "");
+	KUNIT_EXPECT_PTR_EQ(test, val, NULL);
+	KUNIT_EXPECT_STREQ(test, next, "");
+}
+
+static void cmdline_test_next_arg_mixed_tokens(struct kunit *test)
+{
+	char in[] = "bbb= jjj kkk=\"a=b\"";
+	char *next, *param, *val;
+
+	next = next_arg(in, &param, &val);
+	KUNIT_EXPECT_STREQ(test, param, "bbb");
+	KUNIT_ASSERT_NOT_NULL(test, val);
+	KUNIT_EXPECT_STREQ(test, val, "");
+	KUNIT_EXPECT_STREQ(test, next, "jjj kkk=\"a=b\"");
+
+	next = next_arg(next, &param, &val);
+	KUNIT_EXPECT_STREQ(test, param, "jjj");
+	KUNIT_EXPECT_NULL(test, val);
+	KUNIT_EXPECT_STREQ(test, next, "kkk=\"a=b\"");
+
+	next = next_arg(next, &param, &val);
+	KUNIT_EXPECT_STREQ(test, param, "kkk");
+	KUNIT_ASSERT_NOT_NULL(test, val);
+	KUNIT_EXPECT_STREQ(test, val, "a=b");
+	KUNIT_EXPECT_STREQ(test, next, "");
+}
+
+struct cmdline_test_memparse_entry {
+	const char *input;
+	const char *unrecognized;
+	unsigned long long result;
+};
+
+static const struct cmdline_test_memparse_entry testdata[] = {
+	{ "0",				"",	0ULL },
+	{ "1",				"",	1ULL },
+	{ "a",				"a",	0ULL },
+	{ "k",				"k",	0ULL },
+	{ "E",				"E",	0ULL },
+	{ "0xb",			"",	11ULL },
+	{ "0xz",			"x",	0ULL },
+	{ "1234",			"",	1234ULL },
+	{ "04567",			"",	2423ULL },
+	{ "0x9876",			"",	39030LL },
+	{ "05678",			"8",	375ULL },
+	{ "0xabcdefz",			"z",	11259375ULL },
+	{ "0cdba",			"c",	0ULL },
+	{ "4K",				"",	SZ_4K },
+	{ "0x10k@0xaaaabbbb",		"@",	SZ_16K },
+	{ "32M",			"",	SZ_32M },
+	{ "067m:foo",			":",	55 * SZ_1M },
+	{ "2G;bar=baz",			";",	SZ_2G },
+	{ "07gz",			"z",	7ULL * SZ_1G },
+	{ "3T+data",			"+",	3 * SZ_1T },
+	{ "04t,ro",			",",	SZ_4T },
+	{ "012p",			"",	11258999068426240ULL },
+	{ "7P,sync",			",",	7881299347898368ULL },
+	{ "0x2e",			"",	46ULL },
+	{ "2E and more",		" ",	2305843009213693952ULL },
+	{ "18446744073709551615",	"",	ULLONG_MAX },
+	{ "0xffffffffffffffff0",	"",	ULLONG_MAX },
+	{ "1111111111111111111T",	"",	ULLONG_MAX },
+	{ "222222222222222222222G",	"",	ULLONG_MAX },
+	{ "3333333333333333333333M",	"",	ULLONG_MAX },
+};
+
+static void cmdline_test_memparse(struct kunit *test)
+{
+	const struct cmdline_test_memparse_entry *e;
+	unsigned long long ret;
+	char *retptr;
+
+	for (e = testdata; e < testdata + ARRAY_SIZE(testdata); e++) {
+		ret = memparse(e->input, &retptr);
+		KUNIT_EXPECT_EQ_MSG(test, ret, e->result,
+				    "    when parsing '%s'", e->input);
+		KUNIT_EXPECT_EQ_MSG(test, *retptr, *e->unrecognized,
+				    "    when parsing '%s'", e->input);
+	}
+}
+
+static struct kunit_case cmdline_test_cases[] = {
+	KUNIT_CASE(cmdline_test_noint),
+	KUNIT_CASE(cmdline_test_lead_int),
+	KUNIT_CASE(cmdline_test_tail_int),
+	KUNIT_CASE(cmdline_test_range),
+	KUNIT_CASE(cmdline_test_next_arg_quoted_value),
+	KUNIT_CASE(cmdline_test_next_arg_bare_quote_regression),
+	KUNIT_CASE(cmdline_test_next_arg_mixed_tokens),
+	KUNIT_CASE(cmdline_test_memparse),
+	{}
+};
+
+static struct kunit_suite cmdline_test_suite = {
+	.name = "cmdline",
+	.test_cases = cmdline_test_cases,
+};
+kunit_test_suite(cmdline_test_suite);
+
+MODULE_DESCRIPTION("Test cases for API provided by cmdline.c");
+MODULE_LICENSE("GPL");