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([38.34.87.7]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-74af57e1699sm13122736b3a.149.2025.07.02.00.36.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Jul 2025 00:36:28 -0700 (PDT) From: Eduard Zingerman To: bpf@vger.kernel.org, ast@kernel.org Cc: andrii@kernel.org, daniel@iogearbox.net, martin.lau@linux.dev, kernel-team@fb.com, yonghong.song@linux.dev, Eduard Zingerman , Alexei Starovoitov Subject: [PATCH bpf-next v1 1/2] bpf: avoid jump misprediction for PTR_TO_MEM | PTR_UNTRUSTED Date: Wed, 2 Jul 2025 00:36:19 -0700 Message-ID: <20250702073620.897517-1-eddyz87@gmail.com> X-Mailer: git-send-email 2.49.0 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Commit f2362a57aeff ("bpf: allow void* cast using bpf_rdonly_cast()") added a notion of PTR_TO_MEM | MEM_RDONLY | PTR_UNTRUSTED type. This simultaneously introduced a bug in jump prediction logic for situations like below: p = bpf_rdonly_cast(..., 0); if (p) a(); else b(); Here verifier would wrongly predict that else branch cannot be taken. This happens because: - Function reg_not_null() assumes that PTR_TO_MEM w/o PTR_MAYBE_NULL flag cannot be zero. - The call to bpf_rdonly_cast() returns a rdonly_untrusted_mem value w/o PTR_MAYBE_NULL flag. Tracking of PTR_MAYBE_NULL flag for untrusted PTR_TO_MEM does not make sense, as the main purpose of the flag is to catch null pointer access errors. Such errors are not possible on load of PTR_UNTRUSTED values and verifier makes sure that PTR_UNTRUSTED can't be passed to helpers or kfuncs. Hence, modify reg_not_null() to assume that nullness of untrusted PTR_TO_MEM is not known. Fixes: f2362a57aeff ("bpf: allow void* cast using bpf_rdonly_cast()") Suggested-by: Alexei Starovoitov Signed-off-by: Eduard Zingerman --- kernel/bpf/verifier.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index a352b35be479..525a21dbcce3 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -410,7 +410,7 @@ static bool reg_not_null(const struct bpf_reg_state *reg) type == PTR_TO_MAP_KEY || type == PTR_TO_SOCK_COMMON || (type == PTR_TO_BTF_ID && is_trusted_reg(reg)) || - type == PTR_TO_MEM || + (type == PTR_TO_MEM && !(reg->type & PTR_UNTRUSTED)) || type == CONST_PTR_TO_MAP; } -- 2.49.0