From a5ec6ae161d72f01411169a938fa5f8baea16e8f Mon Sep 17 00:00:00 2001 From: Jann Horn Date: Mon, 18 Dec 2017 20:11:58 -0800 Subject: [PATCH] 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 Signed-off-by: Alexei Starovoitov Signed-off-by: Daniel Borkmann --- kernel/bpf/verifier.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 77e4b5223867..102c519836f6 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1059,6 +1059,11 @@ 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;