From: Jann Horn <jannh@google.com>
Date: Tue, 19 Dec 2017 04:11:58 +0000 (-0800)
Subject: bpf: force strict alignment checks for stack pointers
X-Git-Tag: archive/raspbian/4.15.4-1+rpi1~1^2^2~22
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=c4832039dcfbef771a8b58b79fa7254121192eb2;p=linux.git

bpf: force strict alignment checks for stack pointers

Force strict alignment checks for stack pointers because the tracking of
stack spills relies on it; unaligned stack accesses can lead to corruption
of spilled registers, which is exploitable.

Fixes: f1174f77b50c ("bpf/verifier: rework value tracking")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Gbp-Pq: Topic bugfix/all
Gbp-Pq: Name bpf-force-strict-alignment-checks-for-stack-pointers.patch
---

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index a9f9a5e57ba..7d7adf3fb89 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1071,6 +1071,11 @@ static int check_ptr_alignment(struct bpf_verifier_env *env,
 		break;
 	case PTR_TO_STACK:
 		pointer_desc = "stack ";
+		/* The stack spill tracking logic in check_stack_write()
+		 * and check_stack_read() relies on stack accesses being
+		 * aligned.
+		 */
+		strict = true;
 		break;
 	default:
 		break;