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    Subject[PATCH 5.11 029/306] selftests/bpf: Use the last page in test_snprintf_btf on s390
    Date
    From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    From: Ilya Leoshkevich <iii@linux.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@linux.ibm.com>
    Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
    Acked-by: Heiko Carstens <hca@linux.ibm.com>
    Acked-by: Yonghong Song <yhs@fb.com>
    Link: https://lore.kernel.org/bpf/20210227051726.121256-1-iii@linux.ibm.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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;
    }


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