linux-kernel - [PATCH 5.11 029/306] selftests/bpf: Use the last page in test_snprintf

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Date:   Mon, 15 Mar 2021 14:51:32 +0100
From:   gregkh@...uxfoundation.org
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ilya Leoshkevich <iii@...ux.ibm.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Heiko Carstens <hca@...ux.ibm.com>, Yonghong Song <yhs@...com>
Subject: [PATCH 5.11 029/306] selftests/bpf: Use the last page in test_snprintf_btf on s390

From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

From: Ilya Leoshkevich <iii@...ux.ibm.com>

commit 42a382a466a967dc053c73b969cd2ac2fec502cf upstream.

test_snprintf_btf fails on s390, because NULL points to a readable
struct lowcore there. Fix by using the last page instead.

Error message example:

    printing fffffffffffff000 should generate error, got (361)

Fixes: 076a95f5aff2 ("selftests/bpf: Add bpf_snprintf_btf helper tests")
Signed-off-by: Ilya Leoshkevich <iii@...ux.ibm.com>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Acked-by: Heiko Carstens <hca@...ux.ibm.com>
Acked-by: Yonghong Song <yhs@...com>
Link: https://lore.kernel.org/bpf/20210227051726.121256-1-iii@linux.ibm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 tools/testing/selftests/bpf/progs/netif_receive_skb.c |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

--- a/tools/testing/selftests/bpf/progs/netif_receive_skb.c
+++ b/tools/testing/selftests/bpf/progs/netif_receive_skb.c
@@ -16,6 +16,13 @@ bool skip = false;
 #define STRSIZE			2048
 #define EXPECTED_STRSIZE	256
 
+#if defined(bpf_target_s390)
+/* NULL points to a readable struct lowcore on s390, so take the last page */
+#define BADPTR			((void *)0xFFFFFFFFFFFFF000ULL)
+#else
+#define BADPTR			0
+#endif
+
 #ifndef ARRAY_SIZE
 #define ARRAY_SIZE(x)	(sizeof(x) / sizeof((x)[0]))
 #endif
@@ -113,11 +120,11 @@ int BPF_PROG(trace_netif_receive_skb, st
 	}
 
 	/* Check invalid ptr value */
-	p.ptr = 0;
+	p.ptr = BADPTR;
 	__ret = bpf_snprintf_btf(str, STRSIZE, &p, sizeof(p), 0);
 	if (__ret >= 0) {
-		bpf_printk("printing NULL should generate error, got (%d)",
-			   __ret);
+		bpf_printk("printing %llx should generate error, got (%d)",
+			   (unsigned long long)BADPTR, __ret);
 		ret = -ERANGE;
 	}