From e51179a4e09846f8fd0f26a05068520de2b301bf Mon Sep 17 00:00:00 2001 From: Eduard Zingerman Date: Fri, 4 Sep 2026 01:33:22 -0700 Subject: bpf: Don't predict JMP32 pointer vs zero comparisons Consider the following program: r1 = map_value; /* low 32 bits are zero at runtime */ r6 = 0xdead000000000000; if w1 != 0 goto l1; l0: r1 += r6; r2 = *(u64 *)(r1 + 0); exit; l1: r6 = 0; goto l0; At the moment is_branch_taken() reports the jump as always taken, because it does not distinguish between BPF_JMP and BPF_JMP32 comparisons when processing 'if w1 != 0 ...'. Fixes: cac616db39c2 ("bpf: Verifier track null pointer branch_taken with JNE and JEQ") Reported-by: Nicholas Carlini Suggested-by: Nicholas Carlini Signed-off-by: Eduard Zingerman Link: https://lore.kernel.org/bpf/20260904083325.2083493-5-eddyz87@gmail.com Signed-off-by: Kumar Kartikeya Dwivedi --- kernel/bpf/verifier.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 1fb0c832611c..303368460ec1 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -16337,6 +16337,13 @@ static int is_branch_taken(struct bpf_verifier_env *env, struct bpf_reg_state *r if (__is_pointer_value(false, reg1) || __is_pointer_value(false, reg2)) { u64 val; + /* + * The low 32 bits of a valid pointer may well be zero, hence + * nothing below applies to a 32-bit comparison. + */ + if (is_jmp32) + return -1; + /* arrange that reg2 is a scalar, and reg1 is a pointer */ if (!is_reg_const(reg2, is_jmp32)) { opcode = flip_opcode(opcode); -- cgit v1.2.3