On Wed, Apr 14, 2021 at 2:21 AM Florent Revest <revest@xxxxxxxxxxxx> wrote: > > On Wed, Apr 14, 2021 at 1:21 AM Andrii Nakryiko > <andrii.nakryiko@xxxxxxxxx> wrote: > > > > On Mon, Apr 12, 2021 at 8:38 AM Florent Revest <revest@xxxxxxxxxxxx> wrote: > > > > > > This exercises most of the format specifiers. > > > > > > Signed-off-by: Florent Revest <revest@xxxxxxxxxxxx> > > > Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx> > > > --- > > > > As I mentioned on another patch, we probably need negative tests even > > more than positive ones. > > Agreed. > > > I think an easy and nice way to do this is to have a separate BPF > > skeleton where fmt string and arguments are provided through read-only > > global variables, so that user-space can re-use the same BPF skeleton > > to simulate multiple cases. BPF program itself would just call > > bpf_snprintf() and store the returned result. > > Ah, great idea! I was thinking of having one skeleton for each but it > would be a bit much indeed. > > Because the format string needs to be in a read only map though, I > hope it can be modified from userspace before loading. I'll try it out > and see :) if it doesn't work I'll just use more skeletons You need read-only variables (const volatile my_type). Their contents are statically verified by BPF verifier, yet user-space can pre-setup it at runtime. > > > Whether we need to validate the verifier log is up to debate (though > > it's not that hard to do by overriding libbpf_print_fn() callback), > > I'd be ok at least knowing that some bad format strings are rejected > > and don't crash the kernel. > > Alright :) > > > > > > .../selftests/bpf/prog_tests/snprintf.c | 81 +++++++++++++++++++ > > > .../selftests/bpf/progs/test_snprintf.c | 74 +++++++++++++++++ > > > 2 files changed, 155 insertions(+) > > > create mode 100644 tools/testing/selftests/bpf/prog_tests/snprintf.c > > > create mode 100644 tools/testing/selftests/bpf/progs/test_snprintf.c > > > > > > > [...]
