bpf: Don't predict JMP32 pointer vs zero comparisons

Browse source

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: cac616db39 ("bpf: Verifier track null pointer branch_taken with JNE and JEQ")
Reported-by: Nicholas Carlini <npc@anthropic.com>
Suggested-by: Nicholas Carlini <npc@anthropic.com>
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20260904083325.2083493-5-eddyz87@gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

...

This commit is contained in:

Eduard Zingerman 2026-09-04 01:33:22 -07:00 • committed by Kumar Kartikeya Dwivedi

parent bc412b3fb1

commit e51179a4e0

No known key found for this signature in database

GPG key ID: 472D377B63542F83

1 changed files with 7 additions and 0 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

7

kernel/bpf/verifier.c

View file