From a5f7a5bb3b7f28ba7e4fa246775b29a0e5537255 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Tue, 8 Sep 2026 15:37:42 +0800 Subject: x86/kprobes: Fix crash when probing CS CALL instructions 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) Signed-off-by: Jinke Han Signed-off-by: Ingo Molnar Reviewed-by: Masami Hiramatsu (Google) Acked-by: Yafang Shao Acked-by: Borislav Petkov Cc: Peter Zijlstra Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000 --- lib/tests/test_hash.c | 239 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 239 insertions(+) create mode 100644 lib/tests/test_hash.c (limited to 'lib/tests/test_hash.c') diff --git a/lib/tests/test_hash.c b/lib/tests/test_hash.c new file mode 100644 index 000000000..a7af39662 --- /dev/null +++ b/lib/tests/test_hash.c @@ -0,0 +1,239 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Test cases for and + * This just verifies that various ways of computing a hash + * produce the same thing and, for cases where a k-bit hash + * value is requested, is of the requested size. + * + * We fill a buffer with a 255-byte null-terminated string, + * and use both full_name_hash() and hashlen_string() to hash the + * substrings from i to j, where 0 <= i < j < 256. + * + * The returned values are used to check that __hash_32() and + * __hash_32_generic() compute the same thing. Likewise hash_32() + * and hash_64(). + */ + +#include +#include +#include +#include +#include +#include + +/* 32-bit XORSHIFT generator. Seed must not be zero. */ +static u32 __attribute_const__ +xorshift(u32 seed) +{ + seed ^= seed << 13; + seed ^= seed >> 17; + seed ^= seed << 5; + return seed; +} + +/* Given a non-zero x, returns a non-zero byte. */ +static u8 __attribute_const__ +mod255(u32 x) +{ + x = (x & 0xffff) + (x >> 16); /* 1 <= x <= 0x1fffe */ + x = (x & 0xff) + (x >> 8); /* 1 <= x <= 0x2fd */ + x = (x & 0xff) + (x >> 8); /* 1 <= x <= 0x100 */ + x = (x & 0xff) + (x >> 8); /* 1 <= x <= 0xff */ + return x; +} + +/* Fill the buffer with non-zero bytes. */ +static void fill_buf(char *buf, size_t len, u32 seed) +{ + size_t i; + + for (i = 0; i < len; i++) { + seed = xorshift(seed); + buf[i] = mod255(seed); + } +} + +/* Holds most testing variables for the int test. */ +struct test_hash_params { + /* Pointer to integer to be hashed. */ + unsigned long long *h64; + /* Low 32-bits of integer to be hashed. */ + u32 h0; + /* Arch-specific hash result. */ + u32 h1; + /* Generic hash result. */ + u32 h2; + /* ORed hashes of given size (in bits). */ + u32 (*hash_or)[33]; +}; + +#ifdef HAVE_ARCH__HASH_32 +static void +test_int__hash_32(struct kunit *test, struct test_hash_params *params) +{ + params->hash_or[1][0] |= params->h2 = __hash_32_generic(params->h0); +#if HAVE_ARCH__HASH_32 == 1 + KUNIT_EXPECT_EQ_MSG(test, params->h1, params->h2, + "__hash_32(%#x) = %#x != __hash_32_generic() = %#x", + params->h0, params->h1, params->h2); +#endif +} +#endif + +#ifdef HAVE_ARCH_HASH_64 +static void +test_int_hash_64(struct kunit *test, struct test_hash_params *params, u32 const *m, int *k) +{ + params->h2 = hash_64_generic(*params->h64, *k); +#if HAVE_ARCH_HASH_64 == 1 + KUNIT_EXPECT_EQ_MSG(test, params->h1, params->h2, + "hash_64(%#llx, %d) = %#x != hash_64_generic() = %#x", + *params->h64, *k, params->h1, params->h2); +#else + KUNIT_EXPECT_LE_MSG(test, params->h1, params->h2, + "hash_64_generic(%#llx, %d) = %#x > %#x", + *params->h64, *k, params->h1, *m); +#endif +} +#endif + +/* + * Test the various integer hash functions. h64 (or its low-order bits) + * is the integer to hash. hash_or accumulates the OR of the hash values, + * which are later checked to see that they cover all the requested bits. + * + * Because these functions (as opposed to the string hashes) are all + * inline, the code being tested is actually in the module, and you can + * recompile and re-test the module without rebooting. + */ +static void +test_int_hash(struct kunit *test, unsigned long long h64, u32 hash_or[2][33]) +{ + int k; + struct test_hash_params params = { &h64, (u32)h64, 0, 0, hash_or }; + + /* Test __hash32 */ + hash_or[0][0] |= params.h1 = __hash_32(params.h0); +#ifdef HAVE_ARCH__HASH_32 + test_int__hash_32(test, ¶ms); +#endif + + /* Test k = 1..32 bits */ + for (k = 1; k <= 32; k++) { + u32 const m = ((u32)2 << (k-1)) - 1; /* Low k bits set */ + + /* Test hash_32 */ + hash_or[0][k] |= params.h1 = hash_32(params.h0, k); + KUNIT_EXPECT_LE_MSG(test, params.h1, m, + "hash_32(%#x, %d) = %#x > %#x", + params.h0, k, params.h1, m); + + /* Test hash_64 */ + hash_or[1][k] |= params.h1 = hash_64(h64, k); + KUNIT_EXPECT_LE_MSG(test, params.h1, m, + "hash_64(%#llx, %d) = %#x > %#x", + h64, k, params.h1, m); +#ifdef HAVE_ARCH_HASH_64 + test_int_hash_64(test, ¶ms, &m, &k); +#endif + } +} + +#define SIZE 256 /* Run time is cubic in SIZE */ + +static void test_string_or(struct kunit *test) +{ + char buf[SIZE+1]; + u32 string_or = 0; + int i, j; + + fill_buf(buf, SIZE, 1); + + /* Test every possible non-empty substring in the buffer. */ + for (j = SIZE; j > 0; --j) { + buf[j] = '\0'; + + for (i = 0; i <= j; i++) { + u32 h0 = full_name_hash(buf+i, buf+i, j-i); + + string_or |= h0; + } /* i */ + } /* j */ + + /* The OR of all the hash values should cover all the bits */ + KUNIT_EXPECT_EQ_MSG(test, string_or, -1u, + "OR of all string hash results = %#x != %#x", + string_or, -1u); +} + +static void test_hash_or(struct kunit *test) +{ + char buf[SIZE+1]; + u32 hash_or[2][33] = { { 0, } }; + unsigned long long h64 = 0; + int i, j; + + fill_buf(buf, SIZE, 1); + + /* Test every possible non-empty substring in the buffer. */ + for (j = SIZE; j > 0; --j) { + buf[j] = '\0'; + + for (i = 0; i <= j; i++) { + u64 hashlen = hashlen_string(buf+i, buf+i); + u32 h0 = full_name_hash(buf+i, buf+i, j-i); + + /* Check that hashlen_string gets the length right */ + KUNIT_EXPECT_EQ_MSG(test, hashlen_len(hashlen), j-i, + "hashlen_string(%d..%d) returned length %u, expected %d", + i, j, hashlen_len(hashlen), j-i); + /* Check that the hashes match */ + KUNIT_EXPECT_EQ_MSG(test, hashlen_hash(hashlen), h0, + "hashlen_string(%d..%d) = %08x != full_name_hash() = %08x", + i, j, hashlen_hash(hashlen), h0); + + h64 = h64 << 32 | h0; /* For use with hash_64 */ + test_int_hash(test, h64, hash_or); + } /* i */ + } /* j */ + + KUNIT_EXPECT_EQ_MSG(test, hash_or[0][0], -1u, + "OR of all __hash_32 results = %#x != %#x", + hash_or[0][0], -1u); +#ifdef HAVE_ARCH__HASH_32 +#if HAVE_ARCH__HASH_32 != 1 /* Test is pointless if results match */ + KUNIT_EXPECT_EQ_MSG(test, hash_or[1][0], -1u, + "OR of all __hash_32_generic results = %#x != %#x", + hash_or[1][0], -1u); +#endif +#endif + + /* Likewise for all the i-bit hash values */ + for (i = 1; i <= 32; i++) { + u32 const m = ((u32)2 << (i-1)) - 1; /* Low i bits set */ + + KUNIT_EXPECT_EQ_MSG(test, hash_or[0][i], m, + "OR of all hash_32(%d) results = %#x (%#x expected)", + i, hash_or[0][i], m); + KUNIT_EXPECT_EQ_MSG(test, hash_or[1][i], m, + "OR of all hash_64(%d) results = %#x (%#x expected)", + i, hash_or[1][i], m); + } +} + +static struct kunit_case hash_test_cases[] __refdata = { + KUNIT_CASE(test_string_or), + KUNIT_CASE(test_hash_or), + {} +}; + +static struct kunit_suite hash_test_suite = { + .name = "hash", + .test_cases = hash_test_cases, +}; + + +kunit_test_suite(hash_test_suite); + +MODULE_DESCRIPTION("Test cases for and "); +MODULE_LICENSE("GPL"); -- cgit v1.3.1