netdev - [PATCH bpf-next v2 2/3] selftests/bpf: Avoid running unprivileged tests with alignment requirements

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Date:   Wed, 18 Nov 2020 08:16:39 +0100
From:   Björn Töpel <bjorn.topel@...il.com>
To:     ast@...nel.org, daniel@...earbox.net, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Cc:     Björn Töpel <bjorn.topel@...il.com>,
        xi.wang@...il.com, luke.r.nels@...il.com,
        linux-riscv@...ts.infradead.org, andrii.nakryiko@...il.com
Subject: [PATCH bpf-next v2 2/3] selftests/bpf: Avoid running unprivileged tests with alignment requirements

Some architectures have strict alignment requirements. In that case,
the BPF verifier detects if a program has unaligned accesses and
rejects them. A user can pass BPF_F_ANY_ALIGNMENT to a program to
override this check. That, however, will only work when a privileged
user loads a program. An unprivileged user loading a program with this
flag will be rejected prior entering the verifier.

Hence, it does not make sense to load unprivileged programs without
strict alignment when testing the verifier. This patch avoids exactly
that.

Signed-off-by: Björn Töpel <bjorn.topel@...il.com>
---
 tools/testing/selftests/bpf/test_verifier.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index 9be395d9dc64..4bfe3aa2cfc4 100644
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -1152,6 +1152,19 @@ static void get_unpriv_disabled()
 
 static bool test_as_unpriv(struct bpf_test *test)
 {
+#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+	/* Some architectures have strict alignment requirements. In
+	 * that case, the BPF verifier detects if a program has
+	 * unaligned accesses and rejects them. A user can pass
+	 * BPF_F_ANY_ALIGNMENT to a program to override this
+	 * check. That, however, will only work when a privileged user
+	 * loads a program. An unprivileged user loading a program
+	 * with this flag will be rejected prior entering the
+	 * verifier.
+	 */
+	if (test->flags & F_NEEDS_EFFICIENT_UNALIGNED_ACCESS)
+		return false;
+#endif
 	return !test->prog_type ||
 	       test->prog_type == BPF_PROG_TYPE_SOCKET_FILTER ||
 	       test->prog_type == BPF_PROG_TYPE_CGROUP_SKB;
-- 
2.27.0