[PATCH bpf-next v1 01/13] bpf: Refactor ARG_PTR_TO_DYNPTR checks into process_dynptr_func

Kumar Kartikeya Dwivedi
2022-10-18T13:59:40Z

ARG_PTR_TO_DYNPTR is akin to ARG_PTR_TO_TIMER, ARG_PTR_TO_KPTR, where
the underlying register type is subjected to more special checks to
determine the type of object represented by the pointer and its state
consistency.

Move dynptr checks to their own 'process_dynptr_func' function so that
is consistent and in-line with existing code. This also makes it easier
to reuse this code for kfunc handling.

To this end, remove the dependency on bpf_call_arg_meta parameter by
instead taking the uninit_dynptr_regno by pointer. This is only needed
to be set to a valid pointer when arg_type has MEM_UNINIT.

Then, reuse this consolidated function in kfunc dynptr handling too.
Note that for kfuncs, the arg_type constraint of DYNPTR_TYPE_LOCAL has
been lifted.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
include/linux/bpf_verifier.h | 8 +-
kernel/bpf/btf.c | 17 +--
kernel/bpf/verifier.c | 115 ++++++++++--------
.../bpf/prog_tests/kfunc_dynptr_param.c | 5 +-
.../bpf/progs/test_kfunc_dynptr_param.c | 12 --
5 files changed, 69 insertions(+), 88 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 9e1e6965f407..a33683e0618b 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -593,11 +593,9 @@ 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);
-bool is_dynptr_type_expected(struct bpf_verifier_env *env,
- struct bpf_reg_state *reg,
- enum bpf_arg_type arg_type);
+int process_dynptr_func(struct bpf_verifier_env *env, int regno,
+ enum bpf_arg_type arg_type, int argno,
+ u8 *uninit_dynptr_regno);

/* 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 eba603cec2c5..1827d889e08a 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6486,23 +6486,8 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env,
return -EINVAL;
}

- if (!is_dynptr_reg_valid_init(env, reg)) {
- bpf_log(log,
- "arg#%d pointer type %s %s must be valid and initialized\n",
- i, btf_type_str(ref_t),
- ref_tname);
+ if (process_dynptr_func(env, regno, ARG_PTR_TO_DYNPTR, i, NULL))
return -EINVAL;
- }
-
- if (!is_dynptr_type_expected(env, reg,
- ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_LOCAL)) {
- bpf_log(log,
- "arg#%d pointer type %s %s points to unsupported dynamic pointer type\n",
- i, btf_type_str(ref_t),
- ref_tname);
- return -EINVAL;
- }
-
continue;
}

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 6f6d2d511c06..31c0c999448e 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -782,8 +782,7 @@ static bool is_dynptr_reg_valid_uninit(struct bpf_verifier_env *env, struct bpf_
return true;
}

-bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env,
- struct bpf_reg_state *reg)
+static bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
{
struct bpf_func_state *state = func(env, reg);
int spi = get_spi(reg->off);
@@ -802,9 +801,8 @@ bool is_dynptr_reg_valid_init(struct bpf_verifier_env *env,
return true;
}

-bool is_dynptr_type_expected(struct bpf_verifier_env *env,
- struct bpf_reg_state *reg,
- enum bpf_arg_type arg_type)
+static bool is_dynptr_type_expected(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
+ enum bpf_arg_type arg_type)
{
struct bpf_func_state *state = func(env, reg);
enum bpf_dynptr_type dynptr_type;
@@ -5573,6 +5571,65 @@ static int process_kptr_func(struct bpf_verifier_env *env, int regno,
return 0;
}

+int process_dynptr_func(struct bpf_verifier_env *env, int regno,
+ enum bpf_arg_type arg_type, int argno,
+ u8 *uninit_dynptr_regno)
+{
+ struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
+
+ /* We only need to check for initialized / uninitialized helper
+ * dynptr args if the dynptr is not PTR_TO_DYNPTR, as the
+ * assumption is that if it is, that a helper function
+ * initialized the dynptr on behalf of the BPF program.
+ */
+ if (base_type(reg->type) == PTR_TO_DYNPTR)
+ return 0;
+ if (arg_type & MEM_UNINIT) {
+ if (!is_dynptr_reg_valid_uninit(env, reg)) {
+ verbose(env, "Dynptr has to be an uninitialized dynptr\n");
+ return -EINVAL;
+ }
+
+ /* We only support one dynptr being uninitialized at the moment,
+ * which is sufficient for the helper functions we have right now.
+ */
+ if (*uninit_dynptr_regno) {
+ verbose(env, "verifier internal error: multiple uninitialized dynptr args\n");
+ return -EFAULT;
+ }
+
+ *uninit_dynptr_regno = regno;
+ } else {
+ if (!is_dynptr_reg_valid_init(env, reg)) {
+ verbose(env,
+ "Expected an initialized dynptr as arg #%d\n",
+ argno + 1);
+ return -EINVAL;
+ }
+
+ if (!is_dynptr_type_expected(env, reg, arg_type)) {
+ const char *err_extra = "";
+
+ switch (arg_type & DYNPTR_TYPE_FLAG_MASK) {
+ case DYNPTR_TYPE_LOCAL:
+ err_extra = "local";
+ break;
+ case DYNPTR_TYPE_RINGBUF:
+ err_extra = "ringbuf";
+ break;
+ default:
+ err_extra = "<unknown>";
+ break;
+ }
+ verbose(env,
+ "Expected a dynptr of type %s as arg #%d\n",
+ err_extra, argno + 1);
+ return -EINVAL;
+ }
+ }
+ return 0;
+}
+
static bool arg_type_is_mem_size(enum bpf_arg_type type)
{
return type == ARG_CONST_SIZE ||
@@ -6086,52 +6143,8 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
err = check_mem_size_reg(env, reg, regno, true, meta);
break;
case ARG_PTR_TO_DYNPTR:
- /* We only need to check for initialized / uninitialized helper
- * dynptr args if the dynptr is not PTR_TO_DYNPTR, as the
- * assumption is that if it is, that a helper function
- * initialized the dynptr on behalf of the BPF program.
- */
- if (base_type(reg->type) == PTR_TO_DYNPTR)
- break;
- if (arg_type & MEM_UNINIT) {
- if (!is_dynptr_reg_valid_uninit(env, reg)) {
- verbose(env, "Dynptr has to be an uninitialized dynptr\n");
- return -EINVAL;
- }
-
- /* We only support one dynptr being uninitialized at the moment,
- * which is sufficient for the helper functions we have right now.
- */
- if (meta->uninit_dynptr_regno) {
- verbose(env, "verifier internal error: multiple uninitialized dynptr args\n");
- return -EFAULT;
- }
-
- meta->uninit_dynptr_regno = regno;
- } else if (!is_dynptr_reg_valid_init(env, reg)) {
- verbose(env,
- "Expected an initialized dynptr as arg #%d\n",
- arg + 1);
- return -EINVAL;
- } else if (!is_dynptr_type_expected(env, reg, arg_type)) {
- const char *err_extra = "";
-
- switch (arg_type & DYNPTR_TYPE_FLAG_MASK) {
- case DYNPTR_TYPE_LOCAL:
- err_extra = "local";
- break;
- case DYNPTR_TYPE_RINGBUF:
- err_extra = "ringbuf";
- break;
- default:
- err_extra = "<unknown>";
- break;
- }
- verbose(env,
- "Expected a dynptr of type %s as arg #%d\n",
- err_extra, arg + 1);
- return -EINVAL;
- }
+ if (process_dynptr_func(env, regno, arg_type, arg, &meta->uninit_dynptr_regno))
+ return -EACCES;
break;
case ARG_CONST_ALLOC_SIZE_OR_ZERO:
if (!tnum_is_const(reg->var_off)) {
diff --git a/tools/testing/selftests/bpf/prog_tests/kfunc_dynptr_param.c b/tools/testing/selftests/bpf/prog_tests/kfunc_dynptr_param.c
index c210657d4d0a..fc562e863e79 100644
--- a/tools/testing/selftests/bpf/prog_tests/kfunc_dynptr_param.c
+++ b/tools/testing/selftests/bpf/prog_tests/kfunc_dynptr_param.c
@@ -18,10 +18,7 @@ static struct {
const char *expected_verifier_err_msg;
int expected_runtime_err;
} kfunc_dynptr_tests[] = {
- {"dynptr_type_not_supp",
- "arg#0 pointer type STRUCT bpf_dynptr_kern points to unsupported dynamic pointer type", 0},
- {"not_valid_dynptr",
- "arg#0 pointer type STRUCT bpf_dynptr_kern must be valid and initialized", 0},
+ {"not_valid_dynptr", "Expected an initialized dynptr as arg #1", 0},
{"not_ptr_to_stack", "arg#0 pointer type STRUCT bpf_dynptr_kern not to stack", 0},
{"dynptr_data_null", NULL, -EBADMSG},
};
diff --git a/tools/testing/selftests/bpf/progs/test_kfunc_dynptr_param.c b/tools/testing/selftests/bpf/progs/test_kfunc_dynptr_param.c
index ce39d096bba3..f4a8250329b2 100644
--- a/tools/testing/selftests/bpf/progs/test_kfunc_dynptr_param.c
+++ b/tools/testing/selftests/bpf/progs/test_kfunc_dynptr_param.c
@@ -32,18 +32,6 @@ int err, pid;

char _license[] SEC("license") = "GPL";

-SEC("?lsm.s/bpf")
-int BPF_PROG(dynptr_type_not_supp, int cmd, union bpf_attr *attr,
- unsigned int size)
-{
- char write_data[64] = "hello there, world!!";
- struct bpf_dynptr ptr;
-
- bpf_ringbuf_reserve_dynptr(&ringbuf, sizeof(write_data), 0, &ptr);
-
- return bpf_verify_pkcs7_signature(&ptr, &ptr, NULL);
-}
-
SEC("?lsm.s/bpf")
int BPF_PROG(not_valid_dynptr, int cmd, union bpf_attr *attr, unsigned int size)
{
--
2.38.0