[PATCH bpf-next 0/2] Simplify bpf_snprintf verifier code

[PATCH bpf-next 0/2] Simplify bpf_snprintf verifier code

[Florent Revest]

Alexei requested a couple of cleanups to the bpf_snprintf and
ARG_PTR_TO_CONST_STR verifier code.

https://lore.kernel.org/bpf/CABRcYmL_SMT80UTyV98bRsOzW0wBd1sZcYUpTrcOAV+9m+YoWQ@mail.gmail.com/T/#t

Florent Revest (2):
  bpf: Notify user if we ever hit a bpf_snprintf verifier bug
  bpf: Remove unnecessary map checks for ARG_PTR_TO_CONST_STR

 kernel/bpf/verifier.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

-- 
2.31.1.498.g6c1eba8ee3d-goog

[PATCH bpf-next 1/2] bpf: Notify user if we ever hit a bpf_snprintf verifier bug

[Florent Revest]

In check_bpf_snprintf_call(), a map_direct_value_addr() of the fmt map
should never fail because it has already been checked by
ARG_PTR_TO_CONST_STR. But if it ever fails, it's better to error out
with an explicit debug message rather than silently fail.

Signed-off-by: Florent Revest <revest@chromium.org>
Reported-by: Alexei Starovoitov <ast@kernel.org>
---
 kernel/bpf/verifier.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 58730872f7e5..59799a9b014a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5940,8 +5940,10 @@ static int check_bpf_snprintf_call(struct bpf_verifier_env *env,
 	fmt_map_off = fmt_reg->off + fmt_reg->var_off.value;
 	err = fmt_map->ops->map_direct_value_addr(fmt_map, &fmt_addr,
 						  fmt_map_off);
-	if (err)
-		return err;
+	if (err) {
+		verbose(env, "verifier bug\n");
+		return -EFAULT;
+	}
 	fmt = (char *)(long)fmt_addr + fmt_map_off;
 
 	/* We are also guaranteed that fmt+fmt_map_off is NULL terminated, we
-- 
2.31.1.498.g6c1eba8ee3d-goog

[PATCH bpf-next 2/2] bpf: Remove unnecessary map checks for ARG_PTR_TO_CONST_STR

[Florent Revest]

reg->type is enforced by check_reg_type() and map should never be NULL
(it would already have been dereferenced anyway) so these checks are
unnecessary.

Signed-off-by: Florent Revest <revest@chromium.org>
Reported-by: Alexei Starovoitov <ast@kernel.org>
---
 kernel/bpf/verifier.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 59799a9b014a..2579f6fbb5c3 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -5075,8 +5075,7 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 		u64 map_addr;
 		char *str_ptr;
 
-		if (reg->type != PTR_TO_MAP_VALUE || !map ||
-		    !bpf_map_is_rdonly(map)) {
+		if (!bpf_map_is_rdonly(map)) {
 			verbose(env, "R%d does not point to a readonly map'\n", regno);
 			return -EACCES;
 		}
-- 
2.31.1.498.g6c1eba8ee3d-goog

Re: [PATCH bpf-next 0/2] Simplify bpf_snprintf verifier code

[Alexei Starovoitov]

On Thu, Apr 22, 2021 at 4:56 PM Florent Revest <revest@chromium.org> wrote:
>
> Alexei requested a couple of cleanups to the bpf_snprintf and
> ARG_PTR_TO_CONST_STR verifier code.

Applied. Thanks