bpf: Recognize that two registers are safe when their ranges match

Browse source

When open code iterators, bpf_loop or may_goto are used the following two
states are equivalent and safe to prune the search:

cur state: fp-8_w=scalar(id=3,smin=umin=smin32=umin32=2,smax=umax=smax32=umax32=11,var_off=(0x0; 0xf))
old state: fp-8_rw=scalar(id=2,smin=umin=smin32=umin32=1,smax=umax=smax32=umax32=11,var_off=(0x0; 0xf))

In other words "exact" state match should ignore liveness and precision
marks, since open coded iterator logic didn't complete their propagation,
reg_old->type == NOT_INIT && reg_cur->type != NOT_INIT is also not safe to
prune while looping, but range_within logic that applies to scalars,
ptr_to_mem, map_value, pkt_ptr is safe to rely on.

Avoid doing such comparison when regular infinite loop detection logic is
used, otherwise bounded loop logic will declare such "infinite loop" as
false positive. Such example is in progs/verifier_loops1.c
not_an_inifinite_loop().

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Tested-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20240306031929.42666-3-alexei.starovoitov@gmail.com

...

This commit is contained in:

Alexei Starovoitov 2024-03-05 19:19:27 -08:00 • committed by Andrii Nakryiko

parent 011832b97b

commit 4f81c16f50

1 changed files with 30 additions and 21 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

51

kernel/bpf/verifier.c

View file