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/liveupdate.c | 143 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 143 insertions(+) create mode 100644 lib/tests/liveupdate.c (limited to 'lib/tests/liveupdate.c') diff --git a/lib/tests/liveupdate.c b/lib/tests/liveupdate.c new file mode 100644 index 000000000..4c08a7c6f --- /dev/null +++ b/lib/tests/liveupdate.c @@ -0,0 +1,143 @@ +// SPDX-License-Identifier: GPL-2.0 + +/* + * Copyright (c) 2025, Google LLC. + * Pasha Tatashin + */ + +#define pr_fmt(fmt) KBUILD_MODNAME " test: " fmt + +#include +#include +#include +#include +#include +#include "../../kernel/liveupdate/luo_internal.h" + +static const struct liveupdate_flb_ops test_flb_ops; +#define DEFINE_TEST_FLB(i) { \ + .ops = &test_flb_ops, \ + .compatible = LIVEUPDATE_TEST_FLB_COMPATIBLE(i), \ +} + +/* Number of Test FLBs to register with every file handler */ +#define TEST_NFLBS 3 +static struct liveupdate_flb test_flbs[TEST_NFLBS] = { + DEFINE_TEST_FLB(0), + DEFINE_TEST_FLB(1), + DEFINE_TEST_FLB(2), +}; + +#define TEST_FLB_MAGIC_BASE 0xFEEDF00DCAFEBEE0ULL + +static int test_flb_preserve(struct liveupdate_flb_op_args *argp) +{ + ptrdiff_t index = argp->flb - test_flbs; + + pr_info("%s: preserve was triggered\n", argp->flb->compatible); + argp->data = TEST_FLB_MAGIC_BASE + index; + + return 0; +} + +static void test_flb_unpreserve(struct liveupdate_flb_op_args *argp) +{ + pr_info("%s: unpreserve was triggered\n", argp->flb->compatible); +} + +static int test_flb_retrieve(struct liveupdate_flb_op_args *argp) +{ + ptrdiff_t index = argp->flb - test_flbs; + u64 expected_data = TEST_FLB_MAGIC_BASE + index; + + if (argp->data == expected_data) { + pr_info("%s: found flb data from the previous boot\n", + argp->flb->compatible); + argp->obj = (void *)argp->data; + } else { + pr_err("%s: ERROR - incorrect data handle: %llx, expected %llx\n", + argp->flb->compatible, argp->data, expected_data); + return -EINVAL; + } + + return 0; +} + +static void test_flb_finish(struct liveupdate_flb_op_args *argp) +{ + ptrdiff_t index = argp->flb - test_flbs; + void *expected_obj = (void *)(TEST_FLB_MAGIC_BASE + index); + + if (argp->obj == expected_obj) { + pr_info("%s: finish was triggered\n", argp->flb->compatible); + } else { + pr_err("%s: ERROR - finish called with invalid object\n", + argp->flb->compatible); + } +} + +static const struct liveupdate_flb_ops test_flb_ops = { + .preserve = test_flb_preserve, + .unpreserve = test_flb_unpreserve, + .retrieve = test_flb_retrieve, + .finish = test_flb_finish, + .owner = THIS_MODULE, +}; + +static void liveupdate_test_init(void) +{ + static DEFINE_MUTEX(init_lock); + static bool initialized; + int i; + + guard(mutex)(&init_lock); + + if (initialized) + return; + + for (i = 0; i < TEST_NFLBS; i++) { + struct liveupdate_flb *flb = &test_flbs[i]; + void *obj; + int err; + + err = liveupdate_flb_get_incoming(flb, &obj); + if (err && err != -ENODATA && err != -ENOENT) { + pr_err("liveupdate_flb_get_incoming for %s failed: %pe\n", + flb->compatible, ERR_PTR(err)); + } + + if (!err) + liveupdate_flb_put_incoming(flb); + } + initialized = true; +} + +void liveupdate_test_register(struct liveupdate_file_handler *fh) +{ + int err, i; + + liveupdate_test_init(); + + for (i = 0; i < TEST_NFLBS; i++) { + struct liveupdate_flb *flb = &test_flbs[i]; + + err = liveupdate_register_flb(fh, flb); + if (err) { + pr_err("Failed to register %s %pe\n", + flb->compatible, ERR_PTR(err)); + } + } + + err = liveupdate_register_flb(fh, &test_flbs[0]); + if (!err || err != -EEXIST) { + pr_err("Failed: %s should be already registered, but got err: %pe\n", + test_flbs[0].compatible, ERR_PTR(err)); + } + + pr_info("Registered %d FLBs with file handler: [%s]\n", + TEST_NFLBS, fh->compatible); +} + +MODULE_LICENSE("GPL"); +MODULE_AUTHOR("Pasha Tatashin "); +MODULE_DESCRIPTION("In-kernel test for LUO mechanism"); -- cgit v1.3.1