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 --- include/crypto/internal/sig.h | 97 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 97 insertions(+) create mode 100644 include/crypto/internal/sig.h (limited to 'include/crypto/internal/sig.h') diff --git a/include/crypto/internal/sig.h b/include/crypto/internal/sig.h new file mode 100644 index 000000000..b16648c1a --- /dev/null +++ b/include/crypto/internal/sig.h @@ -0,0 +1,97 @@ +/* SPDX-License-Identifier: GPL-2.0-or-later */ +/* + * Public Key Signature Algorithm + * + * Copyright (c) 2023 Herbert Xu + */ +#ifndef _CRYPTO_INTERNAL_SIG_H +#define _CRYPTO_INTERNAL_SIG_H + +#include +#include + +struct sig_instance { + void (*free)(struct sig_instance *inst); + union { + struct { + char head[offsetof(struct sig_alg, base)]; + struct crypto_instance base; + }; + struct sig_alg alg; + }; +}; + +struct crypto_sig_spawn { + struct crypto_spawn base; +}; + +static inline void *crypto_sig_ctx(struct crypto_sig *tfm) +{ + return crypto_tfm_ctx(&tfm->base); +} + +/** + * crypto_register_sig() -- Register public key signature algorithm + * + * Function registers an implementation of a public key signature algorithm + * + * @alg: algorithm definition + * + * Return: zero on success; error code in case of error + */ +int crypto_register_sig(struct sig_alg *alg); + +/** + * crypto_unregister_sig() -- Unregister public key signature algorithm + * + * Function unregisters an implementation of a public key signature algorithm + * + * @alg: algorithm definition + */ +void crypto_unregister_sig(struct sig_alg *alg); + +int sig_register_instance(struct crypto_template *tmpl, + struct sig_instance *inst); + +static inline struct sig_instance *sig_instance(struct crypto_instance *inst) +{ + return container_of(&inst->alg, struct sig_instance, alg.base); +} + +static inline struct sig_instance *sig_alg_instance(struct crypto_sig *tfm) +{ + return sig_instance(crypto_tfm_alg_instance(&tfm->base)); +} + +static inline struct crypto_instance *sig_crypto_instance(struct sig_instance + *inst) +{ + return container_of(&inst->alg.base, struct crypto_instance, alg); +} + +static inline void *sig_instance_ctx(struct sig_instance *inst) +{ + return crypto_instance_ctx(sig_crypto_instance(inst)); +} + +int crypto_grab_sig(struct crypto_sig_spawn *spawn, + struct crypto_instance *inst, + const char *name, u32 type, u32 mask); + +static inline struct crypto_sig *crypto_spawn_sig(struct crypto_sig_spawn + *spawn) +{ + return crypto_spawn_tfm2(&spawn->base); +} + +static inline void crypto_drop_sig(struct crypto_sig_spawn *spawn) +{ + crypto_drop_spawn(&spawn->base); +} + +static inline struct sig_alg *crypto_spawn_sig_alg(struct crypto_sig_spawn + *spawn) +{ + return container_of(spawn->base.alg, struct sig_alg, base); +} +#endif -- cgit v1.3.1