[PATCH v11 2/9] btf: Handle dynamic pointer parameter in kfuncs

From: Roberto Sassu
Date: Fri Aug 12 2022 - 06:20:09 EST


Allow the bpf_dynptr_kern parameter to be specified in kfuncs. Also, ensure
that the dynamic pointer is valid and initialized.

Cc: Joanne Koong <joannelkoong@xxxxxxxxx>
Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
---
include/linux/bpf_verifier.h | 3 +++
kernel/bpf/btf.c | 22 ++++++++++++++++++++++
kernel/bpf/verifier.c | 4 ++--
3 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 2e3bad8640dc..55876fbdbae2 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -560,6 +560,9 @@ int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg_state
u32 regno);
int check_mem_reg(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
u32 regno, u32 mem_size);
+bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env,
+ struct bpf_reg_state *reg,
+ enum bpf_arg_type arg_type);

/* this lives here instead of in bpf.h because it needs to dereference tgt_prog */
static inline u64 bpf_trampoline_compute_key(const struct bpf_prog *tgt_prog,
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index e49b3b6d48ad..86e63f2ee5da 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -195,6 +195,10 @@
i < btf_type_vlen(struct_type); \
i++, member++)

+#define stringify_struct(x) \
+ ({ BUILD_BUG_ON(sizeof(struct x) < 0); \
+ __stringify(x); })
+
DEFINE_IDR(btf_idr);
DEFINE_SPINLOCK(btf_idr_lock);

@@ -6362,15 +6366,20 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,

if (is_kfunc) {
bool arg_mem_size = i + 1 < nargs && is_kfunc_arg_mem_size(btf, &args[i + 1], &regs[regno + 1]);
+ bool arg_dynptr = btf_type_is_struct(ref_t) &&
+ !strcmp(ref_tname,
+ stringify_struct(bpf_dynptr_kern));

/* Permit pointer to mem, but only when argument
* type is pointer to scalar, or struct composed
* (recursively) of scalars.
* When arg_mem_size is true, the pointer can be
* void *.
+ * Also permit initialized dynamic pointers.
*/
if (!btf_type_is_scalar(ref_t) &&
!__btf_type_is_scalar_struct(log, btf, ref_t, 0) &&
+ !arg_dynptr &&
(arg_mem_size ? !btf_type_is_void(ref_t) : 1)) {
bpf_log(log,
"arg#%d pointer type %s %s must point to %sscalar, or struct with scalar\n",
@@ -6378,6 +6387,19 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
return -EINVAL;
}

+ if (arg_dynptr) {
+ if (!is_dynptr_reg_valid_init(env, reg,
+ ARG_PTR_TO_DYNPTR)) {
+ bpf_log(log,
+ "arg#%d pointer type %s %s must be initialized\n",
+ i, btf_type_str(ref_t),
+ ref_tname);
+ return -EINVAL;
+ }
+
+ continue;
+ }
+
/* Check for mem, len pair */
if (arg_mem_size) {
if (check_kfunc_mem_size_reg(env, &regs[regno + 1], regno + 1)) {
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2c1f8069f7b7..aa834e7bb296 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -779,8 +779,8 @@ static bool is_dynptr_reg_valid_uninit(struct bpf_verifier_env *env, struct bpf_
return true;
}

-static bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
- enum bpf_arg_type arg_type)
+bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
+ enum bpf_arg_type arg_type)
{
struct bpf_func_state *state = func(env, reg);
int spi = get_spi(reg->off);
--
2.25.1