BPF verifier bypass / RCE potential via malformed BTF attributes (func_info, line_info, core_relo)
Description
The commit moves BTF validation logic into a dedicated check_btf.c and wires it into the BPF verifier. It hardens handling of BTF-derived information for func_info, line_info, and core_relo, preventing malformed or inconsistent BTF attributes from bypassing the verifier's security checks. This is a genuine security hardening against potential verifier bypasses that could lead to code execution on crafted BPF programs. The change is not merely a dependency update or a cosmetic cleanup; it adds targeted validation paths and integrates them with the verifier flow.
Commit Details
Author: Alexei Starovoitov
Date: 2026-04-12 15:29 UTC
Message:
bpf: Move BTF checking logic into check_btf.c
BTF validation logic is independent from the main verifier.
Move it into check_btf.c
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20260412152936.54262-7-alexei.starovoitov@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Triage Assessment
Vulnerability Type: RCE / Verifier bypass prevention
Confidence: MEDIUM
Reasoning:
The patch introduces dedicated BTF validation paths for BPF programs (func_info, line_info, core_relo) and enforces strict checks during BTF-related info processing. By moving BTF verification into check_btf.c and adding validation for BTF-derived structures, it hardens the BPF verifier against malformed BTF attributes that could otherwise bypass or weaken security guarantees.
Verification Assessment
Vulnerability Type: BPF verifier bypass / RCE potential via malformed BTF attributes (func_info, line_info, core_relo)
Confidence: MEDIUM
Affected Versions: Pre-patch: up to v7.0-rc5 (and earlier); patched in v7.0-rc6 and later.
Code Diff
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 5389af612696d9..53e8664cb566d6 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -1061,6 +1061,11 @@ static inline void bpf_trampoline_unpack_key(u64 key, u32 *obj_id, u32 *btf_id)
*btf_id = key & 0x7FFFFFFF;
}
+int bpf_check_btf_info_early(struct bpf_verifier_env *env,
+ const union bpf_attr *attr, bpfptr_t uattr);
+int bpf_check_btf_info(struct bpf_verifier_env *env,
+ const union bpf_attr *attr, bpfptr_t uattr);
+
int bpf_check_attach_target(struct bpf_verifier_log *log,
const struct bpf_prog *prog,
const struct bpf_prog *tgt_prog,
diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index fd1d901b8d3c3d..399007b67a923e 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -11,7 +11,7 @@ obj-$(CONFIG_BPF_SYSCALL) += bpf_iter.o map_iter.o task_iter.o prog_iter.o link_
obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o bloom_filter.o
obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o ringbuf.o bpf_insn_array.o
obj-$(CONFIG_BPF_SYSCALL) += bpf_local_storage.o bpf_task_storage.o
-obj-$(CONFIG_BPF_SYSCALL) += fixups.o cfg.o states.o backtrack.o
+obj-$(CONFIG_BPF_SYSCALL) += fixups.o cfg.o states.o backtrack.o check_btf.o
obj-${CONFIG_BPF_LSM} += bpf_inode_storage.o
obj-$(CONFIG_BPF_SYSCALL) += disasm.o mprog.o
obj-$(CONFIG_BPF_JIT) += trampoline.o
diff --git a/kernel/bpf/check_btf.c b/kernel/bpf/check_btf.c
new file mode 100644
index 00000000000000..93bebe6fe12e72
--- /dev/null
+++ b/kernel/bpf/check_btf.c
@@ -0,0 +1,463 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+#include <linux/bpf.h>
+#include <linux/bpf_verifier.h>
+#include <linux/filter.h>
+#include <linux/btf.h>
+
+#define verbose(env, fmt, args...) bpf_verifier_log_write(env, fmt, ##args)
+
+static int check_abnormal_return(struct bpf_verifier_env *env)
+{
+ int i;
+
+ for (i = 1; i < env->subprog_cnt; i++) {
+ if (env->subprog_info[i].has_ld_abs) {
+ verbose(env, "LD_ABS is not allowed in subprogs without BTF\n");
+ return -EINVAL;
+ }
+ if (env->subprog_info[i].has_tail_call) {
+ verbose(env, "tail_call is not allowed in subprogs without BTF\n");
+ return -EINVAL;
+ }
+ }
+ return 0;
+}
+
+/* The minimum supported BTF func info size */
+#define MIN_BPF_FUNCINFO_SIZE 8
+#define MAX_FUNCINFO_REC_SIZE 252
+
+static int check_btf_func_early(struct bpf_verifier_env *env,
+ const union bpf_attr *attr,
+ bpfptr_t uattr)
+{
+ u32 krec_size = sizeof(struct bpf_func_info);
+ const struct btf_type *type, *func_proto;
+ u32 i, nfuncs, urec_size, min_size;
+ struct bpf_func_info *krecord;
+ struct bpf_prog *prog;
+ const struct btf *btf;
+ u32 prev_offset = 0;
+ bpfptr_t urecord;
+ int ret = -ENOMEM;
+
+ nfuncs = attr->func_info_cnt;
+ if (!nfuncs) {
+ if (check_abnormal_return(env))
+ return -EINVAL;
+ return 0;
+ }
+
+ urec_size = attr->func_info_rec_size;
+ if (urec_size < MIN_BPF_FUNCINFO_SIZE ||
+ urec_size > MAX_FUNCINFO_REC_SIZE ||
+ urec_size % sizeof(u32)) {
+ verbose(env, "invalid func info rec size %u\n", urec_size);
+ return -EINVAL;
+ }
+
+ prog = env->prog;
+ btf = prog->aux->btf;
+
+ urecord = make_bpfptr(attr->func_info, uattr.is_kernel);
+ min_size = min_t(u32, krec_size, urec_size);
+
+ krecord = kvcalloc(nfuncs, krec_size, GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
+ if (!krecord)
+ return -ENOMEM;
+
+ for (i = 0; i < nfuncs; i++) {
+ ret = bpf_check_uarg_tail_zero(urecord, krec_size, urec_size);
+ if (ret) {
+ if (ret == -E2BIG) {
+ verbose(env, "nonzero tailing record in func info");
+ /* set the size kernel expects so loader can zero
+ * out the rest of the record.
+ */
+ if (copy_to_bpfptr_offset(uattr,
+ offsetof(union bpf_attr, func_info_rec_size),
+ &min_size, sizeof(min_size)))
+ ret = -EFAULT;
+ }
+ goto err_free;
+ }
+
+ if (copy_from_bpfptr(&krecord[i], urecord, min_size)) {
+ ret = -EFAULT;
+ goto err_free;
+ }
+
+ /* check insn_off */
+ ret = -EINVAL;
+ if (i == 0) {
+ if (krecord[i].insn_off) {
+ verbose(env,
+ "nonzero insn_off %u for the first func info record",
+ krecord[i].insn_off);
+ goto err_free;
+ }
+ } else if (krecord[i].insn_off <= prev_offset) {
+ verbose(env,
+ "same or smaller insn offset (%u) than previous func info record (%u)",
+ krecord[i].insn_off, prev_offset);
+ goto err_free;
+ }
+
+ /* check type_id */
+ type = btf_type_by_id(btf, krecord[i].type_id);
+ if (!type || !btf_type_is_func(type)) {
+ verbose(env, "invalid type id %d in func info",
+ krecord[i].type_id);
+ goto err_free;
+ }
+
+ func_proto = btf_type_by_id(btf, type->type);
+ if (unlikely(!func_proto || !btf_type_is_func_proto(func_proto)))
+ /* btf_func_check() already verified it during BTF load */
+ goto err_free;
+
+ prev_offset = krecord[i].insn_off;
+ bpfptr_add(&urecord, urec_size);
+ }
+
+ prog->aux->func_info = krecord;
+ prog->aux->func_info_cnt = nfuncs;
+ return 0;
+
+err_free:
+ kvfree(krecord);
+ return ret;
+}
+
+static int check_btf_func(struct bpf_verifier_env *env,
+ const union bpf_attr *attr,
+ bpfptr_t uattr)
+{
+ const struct btf_type *type, *func_proto, *ret_type;
+ u32 i, nfuncs, urec_size;
+ struct bpf_func_info *krecord;
+ struct bpf_func_info_aux *info_aux = NULL;
+ struct bpf_prog *prog;
+ const struct btf *btf;
+ bpfptr_t urecord;
+ bool scalar_return;
+ int ret = -ENOMEM;
+
+ nfuncs = attr->func_info_cnt;
+ if (!nfuncs) {
+ if (check_abnormal_return(env))
+ return -EINVAL;
+ return 0;
+ }
+ if (nfuncs != env->subprog_cnt) {
+ verbose(env, "number of funcs in func_info doesn't match number of subprogs\n");
+ return -EINVAL;
+ }
+
+ urec_size = attr->func_info_rec_size;
+
+ prog = env->prog;
+ btf = prog->aux->btf;
+
+ urecord = make_bpfptr(attr->func_info, uattr.is_kernel);
+
+ krecord = prog->aux->func_info;
+ info_aux = kzalloc_objs(*info_aux, nfuncs,
+ GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
+ if (!info_aux)
+ return -ENOMEM;
+
+ for (i = 0; i < nfuncs; i++) {
+ /* check insn_off */
+ ret = -EINVAL;
+
+ if (env->subprog_info[i].start != krecord[i].insn_off) {
+ verbose(env, "func_info BTF section doesn't match subprog layout in BPF program\n");
+ goto err_free;
+ }
+
+ /* Already checked type_id */
+ type = btf_type_by_id(btf, krecord[i].type_id);
+ info_aux[i].linkage = BTF_INFO_VLEN(type->info);
+ /* Already checked func_proto */
+ func_proto = btf_type_by_id(btf, type->type);
+
+ ret_type = btf_type_skip_modifiers(btf, func_proto->type, NULL);
+ scalar_return =
+ btf_type_is_small_int(ret_type) || btf_is_any_enum(ret_type);
+ if (i && !scalar_return && env->subprog_info[i].has_ld_abs) {
+ verbose(env, "LD_ABS is only allowed in functions that return 'int'.\n");
+ goto err_free;
+ }
+ if (i && !scalar_return && env->subprog_info[i].has_tail_call) {
+ verbose(env, "tail_call is only allowed in functions that return 'int'.\n");
+ goto err_free;
+ }
+
+ env->subprog_info[i].name = btf_name_by_offset(btf, type->name_off);
+ bpfptr_add(&urecord, urec_size);
+ }
+
+ prog->aux->func_info_aux = info_aux;
+ return 0;
+
+err_free:
+ kfree(info_aux);
+ return ret;
+}
+
+#define MIN_BPF_LINEINFO_SIZE offsetofend(struct bpf_line_info, line_col)
+#define MAX_LINEINFO_REC_SIZE MAX_FUNCINFO_REC_SIZE
+
+static int check_btf_line(struct bpf_verifier_env *env,
+ const union bpf_attr *attr,
+ bpfptr_t uattr)
+{
+ u32 i, s, nr_linfo, ncopy, expected_size, rec_size, prev_offset = 0;
+ struct bpf_subprog_info *sub;
+ struct bpf_line_info *linfo;
+ struct bpf_prog *prog;
+ const struct btf *btf;
+ bpfptr_t ulinfo;
+ int err;
+
+ nr_linfo = attr->line_info_cnt;
+ if (!nr_linfo)
+ return 0;
+ if (nr_linfo > INT_MAX / sizeof(struct bpf_line_info))
+ return -EINVAL;
+
+ rec_size = attr->line_info_rec_size;
+ if (rec_size < MIN_BPF_LINEINFO_SIZE ||
+ rec_size > MAX_LINEINFO_REC_SIZE ||
+ rec_size & (sizeof(u32) - 1))
+ return -EINVAL;
+
+ /* Need to zero it in case the userspace may
+ * pass in a smaller bpf_line_info object.
+ */
+ linfo = kvzalloc_objs(struct bpf_line_info, nr_linfo,
+ GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
+ if (!linfo)
+ return -ENOMEM;
+
+ prog = env->prog;
+ btf = prog->aux->btf;
+
+ s = 0;
+ sub = env->subprog_info;
+ ulinfo = make_bpfptr(attr->line_info, uattr.is_kernel);
+ expected_size = sizeof(struct bpf_line_info);
+ ncopy = min_t(u32, expected_size, rec_size);
+ for (i = 0; i < nr_linfo; i++) {
+ err = bpf_check_uarg_tail_zero(ulinfo, expected_size, rec_size);
+ if (err) {
+ if (err == -E2BIG) {
+ verbose(env, "nonzero tailing record in line_info");
+ if (copy_to_bpfptr_offset(uattr,
+ offsetof(union bpf_attr, line_info_rec_size),
+ &expected_size, sizeof(expected_size)))
+ err = -EFAULT;
+ }
+ goto err_free;
+ }
+
+ if (copy_from_bpfptr(&linfo[i], ulinfo, ncopy)) {
+ err = -EFAULT;
+ goto err_free;
+ }
+
+ /*
+ * Check insn_off to ensure
+ * 1) strictly increasing AND
+ * 2) bounded by prog->len
+ *
+ * The linfo[0].insn_off == 0 check logically falls into
+ * the later "missing bpf_line_info for func..." case
+ * because the first linfo[0].insn_off must be the
+ * first sub also and the first sub must have
+ * subprog_info[0].start == 0.
+ */
+ if ((i && linfo[i].insn_off <= prev_offset) ||
+ linfo[i].insn_off >= prog->len) {
+ verbose(env, "Invalid line_info[%u].insn_off:%u (prev_offset:%u prog->len:%u)\n",
+ i, linfo[i].insn_off, prev_offset,
+ prog->len);
+ err = -EINVAL;
+ goto err_free;
+ }
+
+ if (!prog->insnsi[linfo[i].insn_off].code) {
+ verbose(env,
+ "Invalid insn code at line_info[%u].insn_off\n",
+ i);
+ err = -EINVAL;
+ goto err_free;
+ }
+
+ if (!btf_name_by_offset(btf, linfo[i].line_off) ||
+ !btf_name_by_offset(btf, linfo[i].file_name_off)) {
+ verbose(env, "Invalid line_info[%u].line_off or .file_name_off\n", i);
+ err = -EINVAL;
+ goto err_free;
+ }
+
+ if (s != env->subprog_cnt) {
+ if (linfo[i].insn_off == sub[s].start) {
+ sub[s].linfo_idx = i;
+ s++;
+ } else if (sub[s].start < linfo[i].insn_off) {
+ verbose(env, "missing bpf_line_info for func#%u\n", s);
+ err = -EINVAL;
+ goto err_free;
+ }
+ }
+
+ prev_offset = linfo[i].insn_off;
+ bpfptr_add(&ulinfo, rec_size);
+ }
+
+ if (s != env->subprog_cnt) {
+ verbose(env, "missing bpf_line_info for %u funcs starting from func#%u\n",
+ env->subprog_cnt - s, s);
+ err = -EINVAL;
+ goto err_free;
+ }
+
+ prog->aux->linfo = linfo;
+ prog->aux->nr_linfo = nr_linfo;
+
+ return 0;
+
+err_free:
+ kvfree(linfo);
+ return err;
+}
+
+#define MIN_CORE_RELO_SIZE sizeof(struct bpf_core_relo)
+#define MAX_CORE_RELO_SIZE MAX_FUNCINFO_REC_SIZE
+
+static int check_core_relo(struct bpf_verifier_env *env,
+ const union bpf_attr *attr,
+ bpfptr_t uattr)
+{
+ u32 i, nr_core_relo, ncopy, expected_size, rec_size;
+ struct bpf_core_relo core_relo = {};
+ struct bpf_prog *prog = env->prog;
+ const struct btf *btf = prog->aux->btf;
+ struct bpf_core_ctx ctx = {
+ .log = &env->log,
+ .btf = btf,
+ };
+ bpfptr_t u_core_relo;
+ int err;
+
+ nr_core_relo = attr->core_relo_cnt;
+ if (!nr_core_relo)
+ return 0;
+ if (nr_core_relo > INT_MAX / sizeof(struct bpf_core_relo))
+ return -EINVAL;
+
+ rec_size = attr->core_relo_rec_size;
+ if (rec_size < MIN_CORE_RELO_SIZE ||
+ rec_size > MAX_CORE_RELO_SIZE ||
+ rec_size % sizeof(u32))
+ return -EINVAL;
+
+ u_core_relo = make_bpfptr(attr->core_relos, uattr.is_kernel);
+ expected_size = sizeof(struct bpf_core_relo);
+ ncopy = min_t(u32, expected_size, rec_size);
+
+ /* Unlike func_info and line_info, copy and apply each CO-RE
+ * relocation record one at a time.
+ */
+ for (i = 0; i < nr_core_relo; i++) {
+ /* future proofing when sizeof(bpf_core_relo) changes */
+ err = bpf_check_uarg_tail_zero(u_core_relo, expected_size, rec_size);
+ if (err) {
+ if (err == -E2BIG) {
+ verbose(env, "nonzero tailing record in core_relo");
+ if (copy_to_bpfptr_offset(uattr,
+ offsetof(union bpf_attr, core_relo_rec_size),
+ &expected_size, sizeof(expected_size)))
+ err = -EFAULT;
+ }
+ break;
+ }
+
+ if (copy_from_bpfptr(&core_relo, u_core_relo, ncopy)) {
+ err = -EFAULT;
+ break;
+ }
+
+ if (core_relo.insn_off % 8 || core_relo.insn_off / 8 >= prog->len) {
+ verbose(env, "Invalid core_relo[%u].insn_off:%u prog->len:%u\n",
+ i, core_relo.insn_off, prog->len);
+ err = -EINVAL;
+ break;
+ }
+
+ err = bpf_core_apply(&ctx, &core_relo, i,
+ &prog->insnsi[core_relo.insn_off / 8]);
+ if (err)
+ break;
+ bpfptr_add(&u_core_relo, rec_size);
+ }
+ return err;
+}
+
+int bpf_check_btf_info_early(struct bpf_verifier_env *env,
+ const union bpf_attr *attr,
+ bpfptr_t uattr)
+{
+ struct btf *btf;
+ int err;
+
+ if (!attr->func_info_cnt && !attr->line_info_cnt) {
+ if (check_abnormal_return(env))
+ return -EINVAL;
+ return 0;
+ }
+
+ btf = btf_get_by_fd(attr->prog_btf_fd);
+ if (IS_ERR(btf))
+ return PTR_ERR(btf);
+ if (btf_is_kernel(btf)) {
+ btf_put(btf);
+ return -EACCES;
+ }
+ env->prog->aux->btf = btf;
+
+ err = check_btf_func_early(env, attr, uattr);
+ if (err)
+ return err;
+ return 0;
+}
+
+int bpf_check_btf_info(struct bpf_verifier_env *env,
+ const union bpf_attr *attr,
+ bpfptr_t uattr)
+{
+ int err;
+
+ if (!attr->func_info_cnt && !attr->line_info_cnt) {
+ if (check_abnormal_return(env))
+ return -EINVAL;
+ return 0;
+ }
+
+ err = check_btf_func(env, attr, uattr);
+ if (err)
+ return err;
+
+ err = check_btf_line(env, attr, uattr);
+ if (err)
+ return err;
+
+ err = check_core_relo(env, attr, uattr);
+ if (err)
+ return err;
+
+ return 0;
+}
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index e210dd7205cffa..817eb7815011b4 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -17216,206 +17216,6 @@ static int mark_fastcall_patterns(struct bpf_verifier_env *env)
return 0;
}
-static int check_abnormal_return(struct bpf_verifier_env *env)
-{
- int i;
-
- for (i = 1; i < env->subprog_cnt; i++) {
- if (env->subprog_info[i].has_ld_abs) {
- verbose(env, "LD_ABS is not allowed in subprogs without BTF\n");
- return -EINVAL;
- }
- if (env->subprog_info[i].has_tail_call) {
- verbose(env, "tail_call is not allowed in subprogs without BTF\n");
- return -EINVAL;
- }
- }
- return 0;
-}
-
-/* The minimum supported BTF func info size */
-#define MIN_BPF_FUNCINFO_SIZE 8
-#define MAX_FUNCINFO_REC_SIZE 252
-
-static int check_btf_func_early(struct bpf_verifier_env *env,
- const union bpf_attr *attr,
- bpfptr_t uattr)
-{
- u32 krec_size = sizeof(struct bpf_func_info);
- const struct btf_type *type, *func_proto;
- u32 i, nfuncs, urec_size, min_size;
- struct bpf_func_info *k
... [truncated]