[PATCH bpf 6/9] bpf: force strict alignment checks for stack pointers

[Alexei Starovoitov]

From: Jann Horn <ja...@google.com>

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 <ja...@google.com>
Signed-off-by: Alexei Starovoitov <a...@kernel.org>
---
 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;
-- 
2.9.5