linux-kernel - [PATCH bpf-next v3 4/5] bpf: verifier: Accept dynptr mem as mem in helpers

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Message-ID: <20230506013134.2492210-5-drosen@google.com>
Date:   Fri,  5 May 2023 18:31:33 -0700
From:   Daniel Rosenberg <drosen@...gle.com>
To:     bpf@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Shuah Khan <shuah@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Joanne Koong <joannelkoong@...il.com>,
        Mykola Lysenko <mykolal@...com>, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, kernel-team@...roid.com,
        Daniel Rosenberg <drosen@...gle.com>
Subject: [PATCH bpf-next v3 4/5] bpf: verifier: Accept dynptr mem as mem in helpers

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@...gle.com>
---
 kernel/bpf/verifier.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 7e6bbae9db81..754129d41225 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7495,12 +7495,16 @@ 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;
-- 
2.40.1.521.gf1e218fcd8-goog