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    Subject[PATCH AUTOSEL 4.19 40/83] bpf: fix panic in stack_map_get_build_id() on i386 and arm32
    Date
    From: Song Liu <songliubraving@fb.com>

    [ Upstream commit beaf3d1901f4ea46fbd5c9d857227d99751de469 ]

    As Naresh reported, test_stacktrace_build_id() causes panic on i386 and
    arm32 systems. This is caused by page_address() returns NULL in certain
    cases.

    This patch fixes this error by using kmap_atomic/kunmap_atomic instead
    of page_address.

    Fixes: 615755a77b24 (" bpf: extend stackmap to save binary_build_id+offset instead of address")
    Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
    Signed-off-by: Song Liu <songliubraving@fb.com>
    Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/bpf/stackmap.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
    index 8061a439ef18..e50ef5bca421 100644
    --- a/kernel/bpf/stackmap.c
    +++ b/kernel/bpf/stackmap.c
    @@ -260,7 +260,7 @@ static int stack_map_get_build_id(struct vm_area_struct *vma,
    return -EFAULT; /* page not mapped */

    ret = -EINVAL;
    - page_addr = page_address(page);
    + page_addr = kmap_atomic(page);
    ehdr = (Elf32_Ehdr *)page_addr;

    /* compare magic x7f "ELF" */
    @@ -276,6 +276,7 @@ static int stack_map_get_build_id(struct vm_area_struct *vma,
    else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)
    ret = stack_map_get_build_id_64(page_addr, build_id);
    out:
    + kunmap_atomic(page_addr);
    put_page(page);
    return ret;
    }
    --
    2.19.1
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