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/randstruct_kunit.c | 334 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 334 insertions(+) create mode 100644 lib/tests/randstruct_kunit.c (limited to 'lib/tests/randstruct_kunit.c') diff --git a/lib/tests/randstruct_kunit.c b/lib/tests/randstruct_kunit.c new file mode 100644 index 000000000..f3a2d63c4 --- /dev/null +++ b/lib/tests/randstruct_kunit.c @@ -0,0 +1,334 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Test cases for struct randomization, i.e. CONFIG_RANDSTRUCT=y. + * + * For example, see: + * "Running tests with kunit_tool" at Documentation/dev-tools/kunit/start.rst + * ./tools/testing/kunit/kunit.py run randstruct [--raw_output] \ + * [--make_option LLVM=1] \ + * --kconfig_add CONFIG_RANDSTRUCT_FULL=y + * + */ +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt + +#include +#include +#include +#include +#include + +#define DO_MANY_MEMBERS(macro, args...) \ + macro(a, args) \ + macro(b, args) \ + macro(c, args) \ + macro(d, args) \ + macro(e, args) \ + macro(f, args) \ + macro(g, args) \ + macro(h, args) + +#define do_enum(x, ignored) MEMBER_NAME_ ## x, +enum randstruct_member_names { + DO_MANY_MEMBERS(do_enum) + MEMBER_NAME_MAX, +}; +/* Make sure the macros are working: want 8 test members. */ +_Static_assert(MEMBER_NAME_MAX == 8, "Number of test members changed?!"); + +/* This is an unsigned long member to match the function pointer size */ +#define unsigned_long_member(x, ignored) unsigned long x; +struct randstruct_untouched { + DO_MANY_MEMBERS(unsigned_long_member) +}; + +/* Struct explicitly marked with __randomize_layout. */ +struct randstruct_shuffled { + DO_MANY_MEMBERS(unsigned_long_member) +} __randomize_layout; +#undef unsigned_long_member + +/* Struct implicitly randomized from being all func ptrs. */ +#define func_member(x, ignored) size_t (*x)(int); +struct randstruct_funcs_untouched { + DO_MANY_MEMBERS(func_member) +} __no_randomize_layout; + +struct randstruct_funcs_shuffled { + DO_MANY_MEMBERS(func_member) +}; + +#define func_body(x, ignored) \ +static noinline size_t func_##x(int arg) \ +{ \ + return offsetof(struct randstruct_funcs_untouched, x); \ +} +DO_MANY_MEMBERS(func_body) + +/* Various mixed types. */ +#define mixed_members \ + bool a; \ + short b; \ + unsigned int c __aligned(16); \ + size_t d; \ + char e; \ + u64 f; \ + union { \ + struct randstruct_shuffled shuffled; \ + uintptr_t g; \ + }; \ + union { \ + void *ptr; \ + char h; \ + }; + +struct randstruct_mixed_untouched { + mixed_members +}; + +struct randstruct_mixed_shuffled { + mixed_members +} __randomize_layout; +#undef mixed_members + +struct contains_randstruct_untouched { + int before; + struct randstruct_untouched untouched; + int after; +}; + +struct contains_randstruct_shuffled { + int before; + struct randstruct_shuffled shuffled; + int after; +}; + +struct contains_func_untouched { + struct randstruct_funcs_shuffled inner; + DO_MANY_MEMBERS(func_member) +} __no_randomize_layout; + +struct contains_func_shuffled { + struct randstruct_funcs_shuffled inner; + DO_MANY_MEMBERS(func_member) +}; +#undef func_member + +#define check_mismatch(x, untouched, shuffled) \ + if (offsetof(untouched, x) != offsetof(shuffled, x)) \ + mismatches++; \ + kunit_info(test, #shuffled "::" #x " @ %zu (vs %zu)\n", \ + offsetof(shuffled, x), \ + offsetof(untouched, x)); \ + +#define check_pair(outcome, untouched, shuffled, checker...) \ + mismatches = 0; \ + DO_MANY_MEMBERS(checker, untouched, shuffled) \ + kunit_info(test, "Differing " #untouched " vs " #shuffled " member positions: %d\n", \ + mismatches); \ + KUNIT_##outcome##_MSG(test, mismatches, 0, \ + #untouched " vs " #shuffled " layouts: unlucky or broken?\n"); + +static void randstruct_layout_same(struct kunit *test) +{ + int mismatches; + + check_pair(EXPECT_EQ, struct randstruct_untouched, struct randstruct_untouched, + check_mismatch) + check_pair(EXPECT_GT, struct randstruct_untouched, struct randstruct_shuffled, + check_mismatch) +} + +static void randstruct_layout_mixed(struct kunit *test) +{ + int mismatches; + + check_pair(EXPECT_EQ, struct randstruct_mixed_untouched, struct randstruct_mixed_untouched, + check_mismatch) + check_pair(EXPECT_GT, struct randstruct_mixed_untouched, struct randstruct_mixed_shuffled, + check_mismatch) +} + +static void randstruct_layout_fptr(struct kunit *test) +{ + int mismatches; + + check_pair(EXPECT_EQ, struct randstruct_untouched, struct randstruct_untouched, + check_mismatch) + check_pair(EXPECT_GT, struct randstruct_untouched, struct randstruct_funcs_shuffled, + check_mismatch) + check_pair(EXPECT_GT, struct randstruct_funcs_untouched, struct randstruct_funcs_shuffled, + check_mismatch) +} + +#define check_mismatch_prefixed(x, prefix, untouched, shuffled) \ + check_mismatch(prefix.x, untouched, shuffled) + +static void randstruct_layout_fptr_deep(struct kunit *test) +{ + int mismatches; + + if (IS_ENABLED(CONFIG_CC_IS_CLANG)) + kunit_skip(test, "Clang randstruct misses inner functions: https://github.com/llvm/llvm-project/issues/138355"); + + check_pair(EXPECT_EQ, struct contains_func_untouched, struct contains_func_untouched, + check_mismatch_prefixed, inner) + + check_pair(EXPECT_GT, struct contains_func_untouched, struct contains_func_shuffled, + check_mismatch_prefixed, inner) +} + +#undef check_pair +#undef check_mismatch + +#define check_mismatch(x, ignore) \ + KUNIT_EXPECT_EQ_MSG(test, untouched->x, shuffled->x, \ + "Mismatched member value in %s initializer\n", \ + name); + +static void test_check_init(struct kunit *test, const char *name, + struct randstruct_untouched *untouched, + struct randstruct_shuffled *shuffled) +{ + DO_MANY_MEMBERS(check_mismatch) +} + +static void test_check_mixed_init(struct kunit *test, const char *name, + struct randstruct_mixed_untouched *untouched, + struct randstruct_mixed_shuffled *shuffled) +{ + DO_MANY_MEMBERS(check_mismatch) +} +#undef check_mismatch + +#define check_mismatch(x, ignore) \ + KUNIT_EXPECT_EQ_MSG(test, untouched->untouched.x, \ + shuffled->shuffled.x, \ + "Mismatched member value in %s initializer\n", \ + name); +static void test_check_contained_init(struct kunit *test, const char *name, + struct contains_randstruct_untouched *untouched, + struct contains_randstruct_shuffled *shuffled) +{ + DO_MANY_MEMBERS(check_mismatch) +} +#undef check_mismatch + +#define check_mismatch(x, ignore) \ + KUNIT_EXPECT_PTR_EQ_MSG(test, untouched->x, shuffled->x, \ + "Mismatched member value in %s initializer\n", \ + name); + +static void test_check_funcs_init(struct kunit *test, const char *name, + struct randstruct_funcs_untouched *untouched, + struct randstruct_funcs_shuffled *shuffled) +{ + DO_MANY_MEMBERS(check_mismatch) +} +#undef check_mismatch + +static void randstruct_initializers(struct kunit *test) +{ +#define init_members \ + .a = 1, \ + .b = 3, \ + .c = 5, \ + .d = 7, \ + .e = 11, \ + .f = 13, \ + .g = 17, \ + .h = 19, + struct randstruct_untouched untouched = { + init_members + }; + struct randstruct_shuffled shuffled = { + init_members + }; + struct randstruct_mixed_untouched mixed_untouched = { + init_members + }; + struct randstruct_mixed_shuffled mixed_shuffled = { + init_members + }; + struct contains_randstruct_untouched contains_untouched = { + .untouched = { + init_members + }, + }; + struct contains_randstruct_shuffled contains_shuffled = { + .shuffled = { + init_members + }, + }; +#define func_member(x, ignored) \ + .x = func_##x, + struct randstruct_funcs_untouched funcs_untouched = { + DO_MANY_MEMBERS(func_member) + }; + struct randstruct_funcs_shuffled funcs_shuffled = { + DO_MANY_MEMBERS(func_member) + }; + + test_check_init(test, "named", &untouched, &shuffled); + test_check_init(test, "unnamed", &untouched, + &(struct randstruct_shuffled){ + init_members + }); + + test_check_contained_init(test, "named", &contains_untouched, &contains_shuffled); + test_check_contained_init(test, "unnamed", &contains_untouched, + &(struct contains_randstruct_shuffled){ + .shuffled = (struct randstruct_shuffled){ + init_members + }, + }); + + test_check_contained_init(test, "named", &contains_untouched, &contains_shuffled); + test_check_contained_init(test, "unnamed copy", &contains_untouched, + &(struct contains_randstruct_shuffled){ + /* full struct copy initializer */ + .shuffled = shuffled, + }); + + test_check_mixed_init(test, "named", &mixed_untouched, &mixed_shuffled); + test_check_mixed_init(test, "unnamed", &mixed_untouched, + &(struct randstruct_mixed_shuffled){ + init_members + }); + + test_check_funcs_init(test, "named", &funcs_untouched, &funcs_shuffled); + test_check_funcs_init(test, "unnamed", &funcs_untouched, + &(struct randstruct_funcs_shuffled){ + DO_MANY_MEMBERS(func_member) + }); + +#undef func_member +#undef init_members +} + +static int randstruct_test_init(struct kunit *test) +{ + if (!IS_ENABLED(CONFIG_RANDSTRUCT)) + kunit_skip(test, "Not built with CONFIG_RANDSTRUCT=y"); + + return 0; +} + +static struct kunit_case randstruct_test_cases[] = { + KUNIT_CASE(randstruct_layout_same), + KUNIT_CASE(randstruct_layout_mixed), + KUNIT_CASE(randstruct_layout_fptr), + KUNIT_CASE(randstruct_layout_fptr_deep), + KUNIT_CASE(randstruct_initializers), + {} +}; + +static struct kunit_suite randstruct_test_suite = { + .name = "randstruct", + .init = randstruct_test_init, + .test_cases = randstruct_test_cases, +}; + +kunit_test_suites(&randstruct_test_suite); + +MODULE_DESCRIPTION("Test cases for struct randomization"); +MODULE_LICENSE("GPL"); -- cgit v1.3.1