netdev - [PATCH bpf-next v2 02/15] bpf: make infinite loop detection in is_state

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20240108205209.838365-3-maxtram95@gmail.com>
Date: Mon,  8 Jan 2024 22:51:56 +0200
From: Maxim Mikityanskiy <maxtram95@...il.com>
To: Eduard Zingerman <eddyz87@...il.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Shung-Hsi Yu <shung-hsi.yu@...e.com>
Cc: John Fastabend <john.fastabend@...il.com>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...gle.com>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Mykola Lysenko <mykolal@...com>,
	Shuah Khan <shuah@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	bpf@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	netdev@...r.kernel.org
Subject: [PATCH bpf-next v2 02/15] bpf: make infinite loop detection in is_state_visited() exact

From: Eduard Zingerman <eddyz87@...il.com>

Current infinite loops detection mechanism is speculative:
- first, states_maybe_looping() check is done which simply does memcmp
  for R1-R10 in current frame;
- second, states_equal(..., exact=false) is called. With exact=false
  states_equal() would compare scalars for equality only if in old
  state scalar has precision mark.

Such logic might be problematic if compiler makes some unlucky stack
spill/fill decisions. An artificial example of a false positive looks
as follows:

        r0 = ... unknown scalar ...
        r0 &= 0xff;
        *(u64 *)(r10 - 8) = r0;
        r0 = 0;
    loop:
        r0 = *(u64 *)(r10 - 8);
        if r0 > 10 goto exit_;
        r0 += 1;
        *(u64 *)(r10 - 8) = r0;
        r0 = 0;
        goto loop;

This commit updates call to states_equal to use exact=true, forcing
all scalar comparisons to be exact.

Signed-off-by: Eduard Zingerman <eddyz87@...il.com>
---
 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 adbf330d364b..bc565f445410 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -17023,7 +17023,7 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
 			}
 			/* attempt to detect infinite loop to avoid unnecessary doomed work */
 			if (states_maybe_looping(&sl->state, cur) &&
-			    states_equal(env, &sl->state, cur, false) &&
+			    states_equal(env, &sl->state, cur, true) &&
 			    !iter_active_depths_differ(&sl->state, cur) &&
 			    sl->state.callback_unroll_depth == cur->callback_unroll_depth) {
 				verbose_linfo(env, insn_idx, "; ");
-- 
2.43.0