Add support for passing PTR_TO_BTF_ID registers to global subprogs.
Currently only PTR_TRUSTED flavor of PTR_TO_BTF_ID is supported.
Non-NULL semantics is assumed, so caller will be forced to prove
PTR_TO_BTF_ID can't be NULL.
Note, we disallow global subprogs to destroy passed in PTR_TO_BTF_ID
arguments, even the trusted one. We achieve that by not setting
ref_obj_id when validating subprog code. This basically enforces (in
Rust terms) borrowing semantics vs move semantics. Borrowing semantics
seems to be a better fit for isolated global subprog validation
approach.
Implementation-wise, we utilize existing logic for matching
user-provided BTF type to kernel-side BTF type, used by BPF CO-RE logic
and following same matching rules. We enforce a unique match for types.
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
---
include/linux/bpf_verifier.h | 1 +
kernel/bpf/btf.c | 99 +++++++++++++++++++++++++++++++-----
kernel/bpf/verifier.c | 24 +++++++++
3 files changed, 111 insertions(+), 13 deletions(-)
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 7f5816482a10..0dcde339dc7e 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -610,6 +610,7 @@ struct bpf_subprog_arg_info {
enum bpf_arg_type arg_type;
union {
u32 mem_size;
+ u32 btf_id;
};
};
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 9ec08cfb2967..ed7a05815984 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6985,9 +6985,77 @@ static bool btf_is_dynptr_ptr(const struct btf *btf, const struct btf_type *t)
return false;
}
+struct bpf_cand_cache {
+ const char *name;
+ u32 name_len;
+ u16 kind;
+ u16 cnt;
+ struct {
+ const struct btf *btf;
+ u32 id;
+ } cands[];
+};
+
+static DEFINE_MUTEX(cand_cache_mutex);
+
+static struct bpf_cand_cache *
+bpf_core_find_cands(struct bpf_core_ctx *ctx, u32 local_type_id);
+
+static int btf_get_ptr_to_btf_id(struct bpf_verifier_log *log, int arg_idx,
+ const struct btf *btf, const struct btf_type *t)
+{
+ struct bpf_cand_cache *cc;
+ struct bpf_core_ctx ctx = {
+ .btf = btf,
+ .log = log,
+ };
+ u32 kern_type_id, type_id;
+ int err = 0;
+
+ /* skip PTR and modifiers */
+ type_id = t->type;
+ t = btf_type_by_id(btf, t->type);
+ while (btf_type_is_modifier(t)) {
+ type_id = t->type;
+ t = btf_type_by_id(btf, t->type);
+ }
+
+ mutex_lock(&cand_cache_mutex);
+ cc = bpf_core_find_cands(&ctx, type_id);
+ if (IS_ERR(cc)) {
+ err = PTR_ERR(cc);
+ bpf_log(log, "arg#%d reference type('%s %s') candidate matching error: %d\n",
+ arg_idx, btf_type_str(t), __btf_name_by_offset(btf, t->name_off),
+ err);
+ goto cand_cache_unlock;
+ }
+ if (cc->cnt != 1) {
+ bpf_log(log, "arg#%d reference type('%s %s') %s\n",
+ arg_idx, btf_type_str(t), __btf_name_by_offset(btf, t->name_off),
+ cc->cnt == 0 ? "has no matches" : "is ambiguous");
+ err = cc->cnt == 0 ? -ENOENT : -ESRCH;
+ goto cand_cache_unlock;
+ }
+ if (btf_is_module(cc->cands[0].btf)) {
+ bpf_log(log, "arg#%d reference type('%s %s') points to kernel module type (unsupported)\n",
+ arg_idx, btf_type_str(t), __btf_name_by_offset(btf, t->name_off));
+ err = -EOPNOTSUPP;
+ goto cand_cache_unlock;
+ }
+ kern_type_id = cc->cands[0].id;
+
+cand_cache_unlock:
+ mutex_unlock(&cand_cache_mutex);
+ if (err)
+ return err;
+
+ return kern_type_id;
+}
+
enum btf_arg_tag {
ARG_TAG_CTX = 0x1,
ARG_TAG_NONNULL = 0x2,
+ ARG_TAG_TRUSTED = 0x4,
};
/* Process BTF of a function to produce high-level expectation of function
@@ -7089,6 +7157,8 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
if (strcmp(tag, "ctx") == 0) {
tags |= ARG_TAG_CTX;
+ } else if (strcmp(tag, "trusted") == 0) {
+ tags |= ARG_TAG_TRUSTED;
} else if (strcmp(tag, "nonnull") == 0) {
tags |= ARG_TAG_NONNULL;
} else {
@@ -7127,6 +7197,22 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
sub->args[i].arg_type = ARG_PTR_TO_DYNPTR | MEM_RDONLY;
continue;
}
+ if (tags & ARG_TAG_TRUSTED) {
+ int kern_type_id;
+
+ if (tags & ARG_TAG_NONNULL) {
+ bpf_log(log, "arg#%d has invalid combination of tags\n", i);
+ return -EINVAL;
+ }
+
+ kern_type_id = btf_get_ptr_to_btf_id(log, i, btf, t);
+ if (kern_type_id < 0)
+ return kern_type_id;
+
+ sub->args[i].arg_type = ARG_PTR_TO_BTF_ID | PTR_TRUSTED;
+ sub->args[i].btf_id = kern_type_id;
+ continue;
+ }
if (is_global) { /* generic user data pointer */
u32 mem_size;
@@ -8229,17 +8315,6 @@ size_t bpf_core_essential_name_len(const char *name)
return n;
}
-struct bpf_cand_cache {
- const char *name;
- u32 name_len;
- u16 kind;
- u16 cnt;
- struct {
- const struct btf *btf;
- u32 id;
- } cands[];
-};
-
static void bpf_free_cands(struct bpf_cand_cache *cands)
{
if (!cands->cnt)
@@ -8260,8 +8335,6 @@ static struct bpf_cand_cache *vmlinux_cand_cache[VMLINUX_CAND_CACHE_SIZE];
#define MODULE_CAND_CACHE_SIZE 31
static struct bpf_cand_cache *module_cand_cache[MODULE_CAND_CACHE_SIZE];
-static DEFINE_MUTEX(cand_cache_mutex);
-
static void __print_cand_cache(struct bpf_verifier_log *log,
struct bpf_cand_cache **cache,
int cache_size)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index fe833e831cb6..4879dee8d725 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9336,6 +9336,18 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
ret = process_dynptr_func(env, regno, -1, arg->arg_type, 0);
if (ret)
return ret;
+ } else if (base_type(arg->arg_type) == ARG_PTR_TO_BTF_ID) {
+ struct bpf_call_arg_meta meta;
+ int err;
+
+ if (register_is_null(reg) && type_may_be_null(arg->arg_type))
+ continue;
+
+ memset(&meta, 0, sizeof(meta)); /* leave func_id as zero */
+ err = check_reg_type(env, regno, arg->arg_type, &arg->btf_id, &meta);
+ err = err ?: check_func_arg_reg_off(env, reg, regno, arg->arg_type);
+ if (err)
+ return err;
} else {
bpf_log(log, "verifier bug: unrecognized arg#%d type %d\n",
i, arg->arg_type);
@@ -20137,6 +20149,18 @@ static int do_check_common(struct bpf_verifier_env *env, int subprog)
mark_reg_known_zero(env, regs, i);
reg->mem_size = arg->mem_size;
reg->id = ++env->id_gen;
+ } else if (base_type(arg->arg_type) == ARG_PTR_TO_BTF_ID) {
+ reg->type = PTR_TO_BTF_ID;
+ if (arg->arg_type & PTR_MAYBE_NULL)
+ reg->type |= PTR_MAYBE_NULL;
+ if (arg->arg_type & PTR_UNTRUSTED)
+ reg->type |= PTR_UNTRUSTED;
+ if (arg->arg_type & PTR_TRUSTED)
+ reg->type |= PTR_TRUSTED;
+ mark_reg_known_zero(env, regs, i);
+ reg->btf = bpf_get_btf_vmlinux(); /* can't fail at this point */
+ reg->btf_id = arg->btf_id;
+ reg->id = ++env->id_gen;
} else {
WARN_ONCE(1, "BUG: unhandled arg#%d type %d\n",
i - BPF_REG_1, arg->arg_type);
--
2.34.1
