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/uuid.c | 134 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 134 insertions(+) create mode 100644 lib/uuid.c (limited to 'lib/uuid.c') diff --git a/lib/uuid.c b/lib/uuid.c new file mode 100644 index 000000000..128a51f18 --- /dev/null +++ b/lib/uuid.c @@ -0,0 +1,134 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Unified UUID/GUID definition + * + * Copyright (C) 2009, 2016 Intel Corp. + * Huang Ying + */ + +#include +#include +#include +#include +#include +#include +#include + +const guid_t guid_null; +EXPORT_SYMBOL(guid_null); +const uuid_t uuid_null; +EXPORT_SYMBOL(uuid_null); + +const u8 guid_index[16] = {3,2,1,0,5,4,7,6,8,9,10,11,12,13,14,15}; +const u8 uuid_index[16] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}; + +/** + * generate_random_uuid - generate a random UUID + * @uuid: where to put the generated UUID + * + * Random UUID interface + * + * Used to create a Boot ID or a filesystem UUID/GUID, but can be + * useful for other kernel drivers. + */ +void generate_random_uuid(unsigned char uuid[16]) +{ + get_random_bytes(uuid, 16); + /* Set UUID version to 4 --- truly random generation */ + uuid[6] = (uuid[6] & 0x0F) | 0x40; + /* Set the UUID variant to DCE */ + uuid[8] = (uuid[8] & 0x3F) | 0x80; +} +EXPORT_SYMBOL(generate_random_uuid); + +void generate_random_guid(unsigned char guid[16]) +{ + get_random_bytes(guid, 16); + /* Set GUID version to 4 --- truly random generation */ + guid[7] = (guid[7] & 0x0F) | 0x40; + /* Set the GUID variant to DCE */ + guid[8] = (guid[8] & 0x3F) | 0x80; +} +EXPORT_SYMBOL(generate_random_guid); + +static void __uuid_gen_common(__u8 b[16]) +{ + get_random_bytes(b, 16); + /* revision 0b10 */ + b[8] = (b[8] & 0x3F) | 0x80; +} + +void guid_gen(guid_t *lu) +{ + __uuid_gen_common(lu->b); + /* version 4 : random generation */ + lu->b[7] = (lu->b[7] & 0x0F) | 0x40; +} +EXPORT_SYMBOL_GPL(guid_gen); + +void uuid_gen(uuid_t *bu) +{ + __uuid_gen_common(bu->b); + /* version 4 : random generation */ + bu->b[6] = (bu->b[6] & 0x0F) | 0x40; +} +EXPORT_SYMBOL_GPL(uuid_gen); + +/** + * uuid_is_valid - checks if a UUID string is valid + * @uuid: UUID string to check + * + * Description: + * It checks if the UUID string is following the format: + * xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx + * + * where x is a hex digit. + * + * Return: true if input is valid UUID string. + */ +bool uuid_is_valid(const char *uuid) +{ + unsigned int i; + + for (i = 0; i < UUID_STRING_LEN; i++) { + if (i == 8 || i == 13 || i == 18 || i == 23) { + if (uuid[i] != '-') + return false; + } else if (!isxdigit(uuid[i])) { + return false; + } + } + + return true; +} +EXPORT_SYMBOL(uuid_is_valid); + +static int __uuid_parse(const char *uuid, __u8 b[16], const u8 ei[16]) +{ + static const u8 si[16] = {0,2,4,6,9,11,14,16,19,21,24,26,28,30,32,34}; + unsigned int i; + + if (!uuid_is_valid(uuid)) + return -EINVAL; + + for (i = 0; i < 16; i++) { + int hi = hex_to_bin(uuid[si[i] + 0]); + int lo = hex_to_bin(uuid[si[i] + 1]); + + b[ei[i]] = (hi << 4) | lo; + } + + return 0; +} + +int guid_parse(const char *uuid, guid_t *u) +{ + return __uuid_parse(uuid, u->b, guid_index); +} +EXPORT_SYMBOL(guid_parse); + +int uuid_parse(const char *uuid, uuid_t *u) +{ + return __uuid_parse(uuid, u->b, uuid_index); +} +EXPORT_SYMBOL(uuid_parse); -- cgit v1.3.1