[PATCH bpf-next v9 1/4] bpf: Allow multiple modifiers in reg_type_str() prefix

David Vernet
2022-11-20T05:10:35Z

reg_type_str() in the verifier currently only allows a single register
type modifier to be present in the 'prefix' string which is eventually
stored in the env type_str_buf. This currently works fine because there
are no overlapping type modifiers, but once PTR_TRUSTED is added, that
will no longer be the case. This patch updates reg_type_str() to support
having multiple modifiers in the prefix string, and updates the size of
type_str_buf to be 128 bytes.

Signed-off-by: David Vernet <void@manifault.com>
---
include/linux/bpf_verifier.h | 2 +-
kernel/bpf/verifier.c | 19 ++++++++-----------
2 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index 23f30c685f28..608dde740fef 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -19,7 +19,7 @@
*/
#define BPF_MAX_VAR_SIZ (1 << 29)
/* size of type_str_buf in bpf_verifier. */
-#define TYPE_STR_BUF_LEN 64
+#define TYPE_STR_BUF_LEN 128

/* Liveness marks, used for registers and spilled-regs (in stack slots).
* Read marks propagate upwards until they find a write mark; they record that
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 195d24316750..67a6f11d953c 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -557,7 +557,7 @@ static bool is_cmpxchg_insn(const struct bpf_insn *insn)
static const char *reg_type_str(struct bpf_verifier_env *env,
enum bpf_reg_type type)
{
- char postfix[16] = {0}, prefix[32] = {0};
+ char postfix[16] = {0}, prefix[64] = {0};
static const char * const str[] = {
[NOT_INIT] = "?",
[SCALAR_VALUE] = "scalar",
@@ -589,16 +589,13 @@ static const char *reg_type_str(struct bpf_verifier_env *env,
strncpy(postfix, "_or_null", 16);
}

- if (type & MEM_RDONLY)
- strncpy(prefix, "rdonly_", 32);
- if (type & MEM_RINGBUF)
- strncpy(prefix, "ringbuf_", 32);
- if (type & MEM_USER)
- strncpy(prefix, "user_", 32);
- if (type & MEM_PERCPU)
- strncpy(prefix, "percpu_", 32);
- if (type & PTR_UNTRUSTED)
- strncpy(prefix, "untrusted_", 32);
+ snprintf(prefix, sizeof(prefix), "%s%s%s%s%s",
+ type & MEM_RDONLY ? "rdonly_" : "",
+ type & MEM_RINGBUF ? "ringbuf_" : "",
+ type & MEM_USER ? "user_" : "",
+ type & MEM_PERCPU ? "percpu_" : "",
+ type & PTR_UNTRUSTED ? "untrusted_" : ""
+ );

snprintf(env->type_str_buf, TYPE_STR_BUF_LEN, "%s%s%s",
prefix, str[base_type(type)], postfix);
--
2.38.1