lkml.org 
[lkml]   [2020]   [Nov]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH bpf v2 2/2] selftest/bpf: Test bpf_probe_read_user_str() strips trailing bytes after NUL
    From
    Date
    On Thu Nov 5, 2020 at 3:31 PM PST, Song Liu wrote:
    >
    >
    > > On Nov 5, 2020, at 3:22 PM, Daniel Xu <dxu@dxuuu.xyz> wrote:
    > >
    > > On Thu Nov 5, 2020 at 1:32 PM PST, Andrii Nakryiko wrote:
    > >> On Wed, Nov 4, 2020 at 8:51 PM Daniel Xu <dxu@dxuuu.xyz> wrote:
    > > [...]
    > >>> diff --git a/tools/testing/selftests/bpf/progs/test_probe_read_user_str.c b/tools/testing/selftests/bpf/progs/test_probe_read_user_str.c
    > >>> new file mode 100644
    > >>> index 000000000000..41c3e296566e
    > >>> --- /dev/null
    > >>> +++ b/tools/testing/selftests/bpf/progs/test_probe_read_user_str.c
    > >>> @@ -0,0 +1,34 @@
    > >>> +// SPDX-License-Identifier: GPL-2.0
    > >>> +
    > >>> +#include <linux/bpf.h>
    > >>> +#include <bpf/bpf_helpers.h>
    > >>> +#include <bpf/bpf_tracing.h>
    > >>> +
    > >>> +#include <sys/types.h>
    > >>> +
    > >>> +struct sys_enter_write_args {
    > >>> + unsigned long long pad;
    > >>> + int syscall_nr;
    > >>> + int pad1; /* 4 byte hole */
    > >>
    > >> I have a hunch that this explicit padding might break on big-endian
    > >> architectures?..
    > >>
    > >> Can you instead include "vmlinux.h" in this file and use struct
    > >> trace_event_raw_sys_enter? you'll just need ctx->args[2] to get that
    > >> buffer pointer.
    > >>
    > >> Alternatively, and it's probably simpler overall would be to just
    > >> provide user-space pointer through global variable:
    > >>
    > >> void *user_ptr;
    > >>
    > >>
    > >> bpf_probe_read_user_str(buf, ..., user_ptr);
    > >>
    > >> From user-space:
    > >>
    > >> skel->bss->user_ptr = &my_userspace_buf;
    > >>
    > >> Full control. You can trigger tracepoint with just an usleep(1), for
    > >> instance.
    > >
    > > Yeah, that sounds better. I'll send a v4 with passing a ptr.
    > >
    > > Thanks,
    > > Daniel
    >
    > One more comment, how about we test multiple strings with different
    > lengths? In this way, we can catch other alignment issues.

    Sure, will do that in v4 also.

    \
     
     \ /
      Last update: 2020-11-06 00:57    [W:4.295 / U:1.276 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site