From a5f7a5bb3b7f28ba7e4fa246775b29a0e5537255 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Tue, 8 Sep 2026 15:37:42 +0800 Subject: [PATCH 1/2] 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 --- arch/x86/include/asm/text-patching.h | 4 ++-- arch/x86/kernel/alternative.c | 6 ++++-- arch/x86/kernel/kprobes/core.c | 5 ++--- 3 files changed, 8 insertions(+), 7 deletions(-) diff --git a/arch/x86/include/asm/text-patching.h b/arch/x86/include/asm/text-patching.h index f2d142a0a862..ea09381070e8 100644 --- a/arch/x86/include/asm/text-patching.h +++ b/arch/x86/include/asm/text-patching.h @@ -164,9 +164,9 @@ unsigned long int3_emulate_pop(struct pt_regs *regs) } static __always_inline -void int3_emulate_call(struct pt_regs *regs, unsigned long func) +void int3_emulate_call(struct pt_regs *regs, unsigned long ip, unsigned long func) { - int3_emulate_push(regs, regs->ip - INT3_INSN_SIZE + CALL_INSN_SIZE); + int3_emulate_push(regs, ip); int3_emulate_jmp(regs, func); } diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 741d8767ddf8..582c6d8307d1 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -2176,6 +2176,7 @@ int3_exception_notify(struct notifier_block *self, unsigned long val, void *data unsigned long selftest = (unsigned long)&int3_selftest_asm; struct die_args *args = data; struct pt_regs *regs = args->regs; + unsigned long ip; OPTIMIZER_HIDE_VAR(selftest); @@ -2188,7 +2189,8 @@ int3_exception_notify(struct notifier_block *self, unsigned long val, void *data if (regs->ip - INT3_INSN_SIZE != selftest) return NOTIFY_DONE; - int3_emulate_call(regs, (unsigned long)&int3_selftest_callee); + ip = regs->ip - INT3_INSN_SIZE + CALL_INSN_SIZE; + int3_emulate_call(regs, ip, (unsigned long)&int3_selftest_callee); return NOTIFY_STOP; } @@ -2758,7 +2760,7 @@ noinstr int smp_text_poke_int3_handler(struct pt_regs *regs) break; case CALL_INSN_OPCODE: - int3_emulate_call(regs, (long)ip + tpl->disp); + int3_emulate_call(regs, (long)ip, (long)ip + tpl->disp); break; case JMP32_INSN_OPCODE: diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c index 4e5f8c1736ec..133ff20caccd 100644 --- a/arch/x86/kernel/kprobes/core.c +++ b/arch/x86/kernel/kprobes/core.c @@ -510,10 +510,9 @@ NOKPROBE_SYMBOL(kprobe_emulate_ret); static void kprobe_emulate_call(struct kprobe *p, struct pt_regs *regs) { - unsigned long func = regs->ip - INT3_INSN_SIZE + p->ainsn.size; + unsigned long ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size; - func += p->ainsn.rel32; - int3_emulate_call(regs, func); + int3_emulate_call(regs, ip, ip + p->ainsn.rel32); } NOKPROBE_SYMBOL(kprobe_emulate_call); From 88aed0422f39b22406f35f1e758cea25e7bbcfb5 Mon Sep 17 00:00:00 2001 From: Vinay Belgaumkar Date: Fri, 4 Sep 2026 11:16:24 -0700 Subject: [PATCH 2/2] perf: Fix null pointer access in is_include_guest_event() A typical module unload occurring event when there is an active perf connection leads to freeing of the pmu pointer. The call log is something like: .. __pmu_detach_event pmu_detach_event pmu_detach_events perf_pmu_unregister .. __pmu_detach_event() sets event->pmu to null. When the perf connection finally is closed, the following stack trace is observed: Oops: general protection fault, kernel NULL pointer dereference ... RIP: 0010:_free_event+0x3e/0x370 ... Call Trace: ... perf_event_release_kernel+0x260/0x2d0 perf_release+0x12/0x20 A call to mediated_pmu_unaccount_event() inside _free_event() is the root cause of this crash. Adding a check inside is_include_guest_event() ensures we don't accidentally access a null pmu ptr. In addition to this, we will now call mediated_pmu_unaccount_event() before clearing the pmu ptr so that nr_include_guest_events counts are maintained correctly. Fixes: eff95e170275 ("perf: Add APIs to create/release mediated guest vPMUs") Assisted-by: Claude:Claude-Sonnet-5 Signed-off-by: Vinay Belgaumkar Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Dapeng Mi Link: https://patch.msgid.link/20260904181625.1394082-1-vinay.belgaumkar@intel.com --- kernel/events/core.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/events/core.c b/kernel/events/core.c index fe33fe15689d..db7b76d6b68a 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -6350,6 +6350,9 @@ static DEFINE_MUTEX(perf_mediated_pmu_mutex); /* !exclude_guest event of PMU with PERF_PMU_CAP_MEDIATED_VPMU */ static inline bool is_include_guest_event(struct perf_event *event) { + if (!event->pmu) + return false; + if ((event->pmu->capabilities & PERF_PMU_CAP_MEDIATED_VPMU) && !event->attr.exclude_guest) return true; @@ -13002,6 +13005,7 @@ static void __pmu_detach_event(struct pmu *pmu, struct perf_event *event, exclusive_event_destroy(event); module_put(pmu->module); + mediated_pmu_unaccount_event(event); event->pmu = NULL; /* force fault instead of UAF */ }