[RFC PATCH v3 01/37] bpf: verifier: Accept dynptr mem as mem in herlpers

[Daniel Rosenberg]

This allows using memory retrieved from dynptrs with helper functions
that accept ARG_PTR_TO_MEM. For instance, results from bpf_dynptr_data
can be passed along to bpf_strncmp.

Signed-off-by: Daniel Rosenberg <drosen@xxxxxxxxxx>
---
 kernel/bpf/verifier.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1e05355facdc..ebc638bfed87 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7128,12 +7128,16 @@ static int check_reg_type(struct bpf_verifier_env *env, u32 regno,
 	 * ARG_PTR_TO_MEM + MAYBE_NULL is compatible with PTR_TO_MEM and PTR_TO_MEM + MAYBE_NULL,
 	 * but ARG_PTR_TO_MEM is compatible only with PTR_TO_MEM but NOT with PTR_TO_MEM + MAYBE_NULL
 	 *
+	 * ARG_PTR_TO_MEM is compatible with PTR_TO_MEM that is tagged with a dynptr type.
+	 *
 	 * Therefore we fold these flags depending on the arg_type before comparison.
 	 */
 	if (arg_type & MEM_RDONLY)
 		type &= ~MEM_RDONLY;
 	if (arg_type & PTR_MAYBE_NULL)
 		type &= ~PTR_MAYBE_NULL;
+	if (base_type(arg_type) == ARG_PTR_TO_MEM)
+		type &= ~DYNPTR_TYPE_FLAG_MASK;
 
 	if (meta->func_id == BPF_FUNC_kptr_xchg && type & MEM_ALLOC)
 		type &= ~MEM_ALLOC;
-- 
2.40.0.634.g4ca3ef3211-goog