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 --- fs/fs_parser.c | 390 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 390 insertions(+) create mode 100644 fs/fs_parser.c (limited to 'fs/fs_parser.c') diff --git a/fs/fs_parser.c b/fs/fs_parser.c new file mode 100644 index 000000000..b4cc4cce5 --- /dev/null +++ b/fs/fs_parser.c @@ -0,0 +1,390 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* Filesystem parameter parser. + * + * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved. + * Written by David Howells (dhowells@redhat.com) + */ + +#include +#include +#include +#include +#include +#include +#include "internal.h" + +static const struct constant_table bool_names[] = { + { "0", false }, + { "1", true }, + { "false", false }, + { "no", false }, + { "true", true }, + { "yes", true }, + { }, +}; + +static const struct constant_table * +__lookup_constant(const struct constant_table *tbl, const char *name) +{ + for ( ; tbl->name; tbl++) + if (strcmp(name, tbl->name) == 0) + return tbl; + return NULL; +} + +/** + * lookup_constant - Look up a constant by name in an ordered table + * @tbl: The table of constants to search. + * @name: The name to look up. + * @not_found: The value to return if the name is not found. + */ +int lookup_constant(const struct constant_table *tbl, const char *name, int not_found) +{ + const struct constant_table *p = __lookup_constant(tbl, name); + + return p ? p->value : not_found; +} +EXPORT_SYMBOL(lookup_constant); + +static inline bool is_flag(const struct fs_parameter_spec *p) +{ + return p->type == NULL; +} + +static const struct fs_parameter_spec *fs_lookup_key( + const struct fs_parameter_spec *desc, + struct fs_parameter *param, bool *negated) +{ + const struct fs_parameter_spec *p, *other = NULL; + const char *name = param->key; + bool want_flag = param->type == fs_value_is_flag; + + *negated = false; + for (p = desc; p->name; p++) { + if (strcmp(p->name, name) != 0) + continue; + if (likely(is_flag(p) == want_flag)) + return p; + other = p; + } + if (want_flag) { + if (name[0] == 'n' && name[1] == 'o' && name[2]) { + for (p = desc; p->name; p++) { + if (strcmp(p->name, name + 2) != 0) + continue; + if (!(p->flags & fs_param_neg_with_no)) + continue; + *negated = true; + return p; + } + } + } + return other; +} + +/* + * __fs_parse - Parse a filesystem configuration parameter + * @log: The filesystem context to log errors through. + * @desc: The parameter description to use. + * @param: The parameter. + * @result: Where to place the result of the parse + * + * Parse a filesystem configuration parameter and attempt a conversion for a + * simple parameter for which this is requested. If successful, the determined + * parameter ID is placed into @result->key, the desired type is indicated in + * @result->t and any converted value is placed into an appropriate member of + * the union in @result. + * + * The function returns the parameter number if the parameter was matched, + * -ENOPARAM if it wasn't matched and @desc->ignore_unknown indicated that + * unknown parameters are okay and -EINVAL if there was a conversion issue or + * the parameter wasn't recognised and unknowns aren't okay. + */ +int __fs_parse(struct p_log *log, + const struct fs_parameter_spec *desc, + struct fs_parameter *param, + struct fs_parse_result *result) +{ + const struct fs_parameter_spec *p; + + result->uint_64 = 0; + + p = fs_lookup_key(desc, param, &result->negated); + if (!p) + return -ENOPARAM; + + if (p->flags & fs_param_deprecated) + warn_plog(log, "Deprecated parameter '%s'", param->key); + + /* Try to turn the type we were given into the type desired by the + * parameter and give an error if we can't. + */ + if (is_flag(p)) { + if (param->type != fs_value_is_flag) + return inval_plog(log, "Unexpected value for '%s'", + param->key); + result->boolean = !result->negated; + } else { + int ret = p->type(log, p, param, result); + if (ret) + return ret; + } + return p->opt; +} +EXPORT_SYMBOL(__fs_parse); + +/** + * fs_lookup_param - Look up a path referred to by a parameter + * @fc: The filesystem context to log errors through. + * @param: The parameter. + * @want_bdev: T if want a blockdev + * @flags: Pathwalk flags passed to filename_lookup() + * @_path: The result of the lookup + */ +int fs_lookup_param(struct fs_context *fc, + struct fs_parameter *param, + bool want_bdev, + unsigned int flags, + struct path *_path) +{ + struct filename *f; + bool put_f; + int ret; + + switch (param->type) { + case fs_value_is_string: + f = getname_kernel(param->string); + if (IS_ERR(f)) + return PTR_ERR(f); + param->dirfd = AT_FDCWD; + put_f = true; + break; + case fs_value_is_filename: + f = param->name; + put_f = false; + break; + default: + return invalf(fc, "%s: not usable as path", param->key); + } + + ret = filename_lookup(param->dirfd, f, flags, _path, NULL); + if (ret < 0) { + errorf(fc, "%s: Lookup failure for '%s'", param->key, f->name); + goto out; + } + + if (want_bdev && + !S_ISBLK(d_backing_inode(_path->dentry)->i_mode)) { + path_put(_path); + _path->dentry = NULL; + _path->mnt = NULL; + errorf(fc, "%s: Non-blockdev passed as '%s'", + param->key, f->name); + ret = -ENOTBLK; + } + +out: + if (put_f) + putname(f); + return ret; +} +EXPORT_SYMBOL(fs_lookup_param); + +static int fs_param_bad_value(struct p_log *log, struct fs_parameter *param) +{ + return inval_plog(log, "Bad value for '%s'", param->key); +} + +int fs_param_is_bool(struct p_log *log, const struct fs_parameter_spec *p, + struct fs_parameter *param, struct fs_parse_result *result) +{ + int b; + if (param->type != fs_value_is_string) + return fs_param_bad_value(log, param); + if (!*param->string && (p->flags & fs_param_can_be_empty)) + return 0; + b = lookup_constant(bool_names, param->string, -1); + if (b == -1) + return fs_param_bad_value(log, param); + result->boolean = b; + return 0; +} +EXPORT_SYMBOL(fs_param_is_bool); + +int fs_param_is_u32(struct p_log *log, const struct fs_parameter_spec *p, + struct fs_parameter *param, struct fs_parse_result *result) +{ + int base = (unsigned long)p->data; + if (param->type != fs_value_is_string) + return fs_param_bad_value(log, param); + if (!*param->string && (p->flags & fs_param_can_be_empty)) + return 0; + if (kstrtouint(param->string, base, &result->uint_32) < 0) + return fs_param_bad_value(log, param); + return 0; +} +EXPORT_SYMBOL(fs_param_is_u32); + +int fs_param_is_s32(struct p_log *log, const struct fs_parameter_spec *p, + struct fs_parameter *param, struct fs_parse_result *result) +{ + if (param->type != fs_value_is_string) + return fs_param_bad_value(log, param); + if (!*param->string && (p->flags & fs_param_can_be_empty)) + return 0; + if (kstrtoint(param->string, 0, &result->int_32) < 0) + return fs_param_bad_value(log, param); + return 0; +} +EXPORT_SYMBOL(fs_param_is_s32); + +int fs_param_is_u64(struct p_log *log, const struct fs_parameter_spec *p, + struct fs_parameter *param, struct fs_parse_result *result) +{ + if (param->type != fs_value_is_string) + return fs_param_bad_value(log, param); + if (!*param->string && (p->flags & fs_param_can_be_empty)) + return 0; + if (kstrtoull(param->string, 0, &result->uint_64) < 0) + return fs_param_bad_value(log, param); + return 0; +} +EXPORT_SYMBOL(fs_param_is_u64); + +int fs_param_is_enum(struct p_log *log, const struct fs_parameter_spec *p, + struct fs_parameter *param, struct fs_parse_result *result) +{ + const struct constant_table *c; + if (param->type != fs_value_is_string) + return fs_param_bad_value(log, param); + if (!*param->string && (p->flags & fs_param_can_be_empty)) + return 0; + c = __lookup_constant(p->data, param->string); + if (!c) + return fs_param_bad_value(log, param); + result->uint_32 = c->value; + return 0; +} +EXPORT_SYMBOL(fs_param_is_enum); + +int fs_param_is_string(struct p_log *log, const struct fs_parameter_spec *p, + struct fs_parameter *param, struct fs_parse_result *result) +{ + if (param->type != fs_value_is_string || + (!*param->string && !(p->flags & fs_param_can_be_empty))) + return fs_param_bad_value(log, param); + return 0; +} +EXPORT_SYMBOL(fs_param_is_string); + +int fs_param_is_fd(struct p_log *log, const struct fs_parameter_spec *p, + struct fs_parameter *param, struct fs_parse_result *result) +{ + switch (param->type) { + case fs_value_is_string: + if ((!*param->string && !(p->flags & fs_param_can_be_empty)) || + kstrtouint(param->string, 0, &result->uint_32) < 0) + break; + if (result->uint_32 <= INT_MAX) + return 0; + break; + case fs_value_is_file: + result->uint_32 = param->dirfd; + if (result->uint_32 <= INT_MAX) + return 0; + break; + default: + break; + } + return fs_param_bad_value(log, param); +} +EXPORT_SYMBOL(fs_param_is_fd); + +int fs_param_is_file_or_string(struct p_log *log, + const struct fs_parameter_spec *p, + struct fs_parameter *param, + struct fs_parse_result *result) +{ + switch (param->type) { + case fs_value_is_string: + return fs_param_is_string(log, p, param, result); + case fs_value_is_file: + result->uint_32 = param->dirfd; + if (result->uint_32 <= INT_MAX) + return 0; + break; + default: + break; + } + return fs_param_bad_value(log, param); +} +EXPORT_SYMBOL(fs_param_is_file_or_string); + +int fs_param_is_uid(struct p_log *log, const struct fs_parameter_spec *p, + struct fs_parameter *param, struct fs_parse_result *result) +{ + kuid_t uid; + + if (fs_param_is_u32(log, p, param, result) != 0) + return fs_param_bad_value(log, param); + + uid = make_kuid(current_user_ns(), result->uint_32); + if (!uid_valid(uid)) + return inval_plog(log, "Invalid uid '%s'", param->string); + + result->uid = uid; + return 0; +} +EXPORT_SYMBOL(fs_param_is_uid); + +int fs_param_is_gid(struct p_log *log, const struct fs_parameter_spec *p, + struct fs_parameter *param, struct fs_parse_result *result) +{ + kgid_t gid; + + if (fs_param_is_u32(log, p, param, result) != 0) + return fs_param_bad_value(log, param); + + gid = make_kgid(current_user_ns(), result->uint_32); + if (!gid_valid(gid)) + return inval_plog(log, "Invalid gid '%s'", param->string); + + result->gid = gid; + return 0; +} +EXPORT_SYMBOL(fs_param_is_gid); + +int fs_param_is_blockdev(struct p_log *log, const struct fs_parameter_spec *p, + struct fs_parameter *param, struct fs_parse_result *result) +{ + return 0; +} +EXPORT_SYMBOL(fs_param_is_blockdev); + +#ifdef CONFIG_VALIDATE_FS_PARSER +/** + * fs_validate_description - Validate a parameter specification array + * @name: Owner name of the parameter specification array + * @desc: The parameter specification array to validate. + */ +bool fs_validate_description(const char *name, + const struct fs_parameter_spec *desc) +{ + const struct fs_parameter_spec *param, *p2; + bool good = true; + + for (param = desc; param->name; param++) { + /* Check for duplicate parameter names */ + for (p2 = desc; p2 < param; p2++) { + if (strcmp(param->name, p2->name) == 0) { + if (is_flag(param) != is_flag(p2)) + continue; + pr_err("VALIDATE %s: PARAM[%s]: Duplicate\n", + name, param->name); + good = false; + } + } + } + return good; +} +#endif /* CONFIG_VALIDATE_FS_PARSER */ -- cgit v1.3.1