Re: [PATCHv3 bpf-next 7/9] selftests/bpf: Allow to use kfunc from testmod.ko in test_verifier

Jiri Olsa
2023-02-08T10:10:32Z

On Tue, Feb 07, 2023 at 09:34:26AM -0600, David Vernet wrote:
> On Fri, Feb 03, 2023 at 05:23:34PM +0100, Jiri Olsa wrote:
> > Currently the test_verifier allows test to specify kfunc symbol
> > and search for it in the kernel BTF.
> >
> > Adding the possibility to search for kfunc also in bpf_testmod
> > module when it's not found in kernel BTF.
> >
> > To find bpf_testmod btf we need to get back SYS_ADMIN cap.
>
> This observation and any subsequent discussion is certainly outside the
> scope of your patch set, but it feels like a bit of a weird /
> inconsistent UX to force users to have SYS_ADMIN cap for loading kfuncs
> from modules, but not from vmlinux BTF.
>
> I realize that you need to have SYS_ADMIN cap for BPF_PROG_GET_FD_BY_ID,
> BPF_MAP_GET_FD_BY_ID, etc, so the consistency makes sense there, but it
> would be nice if we could eventually make the UX consistent for programs
> linking against module kfuncs, because I don't really see the difference
> in terms of permissions from the user's perspective.

right, it's tricky.. I'm not sure if BPF_PROG_GET_FD_BY_ID could
work just with CAP_BPF.. will check

>
> >
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
>
> LGTM in general -- just left one comment below.
>
> Acked-by: David Vernet <void@manifault.com>
>
> > ---
> > tools/testing/selftests/bpf/test_verifier.c | 161 +++++++++++++++++---
> > 1 file changed, 139 insertions(+), 22 deletions(-)
> >
> > diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
> > index 14f11f2dfbce..0a570195be37 100644
> > --- a/tools/testing/selftests/bpf/test_verifier.c
> > +++ b/tools/testing/selftests/bpf/test_verifier.c
> > @@ -879,8 +879,140 @@ static int create_map_kptr(void)
> > return fd;
> > }
> >
> > +static void set_root(bool set)
> > +{
> > + __u64 caps;
> > +
> > + if (set) {
> > + if (cap_enable_effective(1ULL << CAP_SYS_ADMIN, &caps))
> > + perror("cap_disable_effective(CAP_SYS_ADMIN)");
> > + } else {
> > + if (cap_disable_effective(1ULL << CAP_SYS_ADMIN, &caps))
> > + perror("cap_disable_effective(CAP_SYS_ADMIN)");
> > + }
> > +}
> > +
> > +static inline __u64 ptr_to_u64(const void *ptr)
> > +{
> > + return (__u64) (unsigned long) ptr;
>
> Small nit / suggestion -- IMO this is slightly preferable just to keep
> it a bit more in-line with the C-standard:
>
> return (uintptr_t)ptr;
>
> The standard of course doesn't dictate that you can do
> ptr -> uintptr_t -> __u64 -> uintptr_t -> ptr, but it at least does dictate that you can do
> ptr -> uintptr_t -> ptr, whereas it does not say the same for
> ptr -> unsigned long -> ptr
>
> Also, I don't think the 'inline' keyword is necessary. The compiler will
> probably figure this out on its own.

I copy&paste the ptr_to_u64 from some other test, sounds good, will check

>
> > +}
> > +
> > +static struct btf *btf__load_testmod_btf(struct btf *vmlinux)
>
> Would be nice if some of this code could be shared from libbpf at some
> point, but ok, a cleanup for another time.

ok

thanks,
jirka

>
> > +{
> > + struct bpf_btf_info info;
> > + __u32 len = sizeof(info);
> > + struct btf *btf = NULL;
> > + char name[64];
> > + __u32 id = 0;
> > + int err, fd;
> > +
> > + /* Iterate all loaded BTF objects and find bpf_testmod,
> > + * we need SYS_ADMIN cap for that.
> > + */
> > + set_root(true);
> > +
> > + while (true) {
> > + err = bpf_btf_get_next_id(id, &id);
> > + if (err) {
> > + if (errno == ENOENT)
> > + break;
> > + perror("bpf_btf_get_next_id failed");
> > + break;
> > + }
> > +
> > + fd = bpf_btf_get_fd_by_id(id);
> > + if (fd < 0) {
> > + if (errno == ENOENT)
> > + continue;
> > + perror("bpf_btf_get_fd_by_id failed");
> > + break;
> > + }
> > +
> > + memset(&info, 0, sizeof(info));
> > + info.name_len = sizeof(name);
> > + info.name = ptr_to_u64(name);
> > + len = sizeof(info);
> > +
> > + err = bpf_obj_get_info_by_fd(fd, &info, &len);
> > + if (err) {
> > + close(fd);
> > + perror("bpf_obj_get_info_by_fd failed");
> > + break;
> > + }
> > +
> > + if (strcmp("bpf_testmod", name)) {
> > + close(fd);
> > + continue;
> > + }
> > +
> > + btf = btf__load_from_kernel_by_id_split(id, vmlinux);
> > + if (!btf) {
> > + close(fd);
> > + break;
> > + }
> > +
> > + /* We need the fd to stay open so it can be used in fd_array.
> > + * The final cleanup call to btf__free will free btf object
> > + * and close the file descriptor.
> > + */
> > + btf__set_fd(btf, fd);
> > + break;
> > + }
> > +
> > + set_root(false);
> > + return btf;
> > +}
> > +
> > +static struct btf *testmod_btf;
> > +static struct btf *vmlinux_btf;
> > +
> > +static void kfuncs_cleanup(void)
> > +{
> > + btf__free(testmod_btf);
> > + btf__free(vmlinux_btf);
> > +}
> > +
> > +static void fixup_prog_kfuncs(struct bpf_insn *prog, int *fd_array,
> > + struct kfunc_btf_id_pair *fixup_kfunc_btf_id)
> > +{
> > + /* Patch in kfunc BTF IDs */
> > + while (fixup_kfunc_btf_id->kfunc) {
> > + int btf_id = 0;
> > +
> > + /* try to find kfunc in kernel BTF */
> > + vmlinux_btf = vmlinux_btf ?: btf__load_vmlinux_btf();
> > + if (vmlinux_btf) {
> > + btf_id = btf__find_by_name_kind(vmlinux_btf,
> > + fixup_kfunc_btf_id->kfunc,
> > + BTF_KIND_FUNC);
> > + btf_id = btf_id < 0 ? 0 : btf_id;
> > + }
> > +
> > + /* kfunc not found in kernel BTF, try bpf_testmod BTF */
> > + if (!btf_id) {
> > + testmod_btf = testmod_btf ?: btf__load_testmod_btf(vmlinux_btf);
> > + if (testmod_btf) {
> > + btf_id = btf__find_by_name_kind(testmod_btf,
> > + fixup_kfunc_btf_id->kfunc,
> > + BTF_KIND_FUNC);
> > + btf_id = btf_id < 0 ? 0 : btf_id;
> > + if (btf_id) {
> > + /* We put bpf_testmod module fd into fd_array
> > + * and its index 1 into instruction 'off'.
> > + */
> > + *fd_array = btf__fd(testmod_btf);
> > + prog[fixup_kfunc_btf_id->insn_idx].off = 1;
> > + }
> > + }
> > + }
> > +
> > + prog[fixup_kfunc_btf_id->insn_idx].imm = btf_id;
> > + fixup_kfunc_btf_id++;
> > + }
> > +}
> > +
> > static void do_test_fixup(struct bpf_test *test, enum bpf_prog_type prog_type,
> > - struct bpf_insn *prog, int *map_fds)
> > + struct bpf_insn *prog, int *map_fds, int *fd_array)
> > {
> > int *fixup_map_hash_8b = test->fixup_map_hash_8b;
> > int *fixup_map_hash_48b = test->fixup_map_hash_48b;
> > @@ -905,7 +1037,6 @@ static void do_test_fixup(struct bpf_test *test, enum bpf_prog_type prog_type,
> > int *fixup_map_ringbuf = test->fixup_map_ringbuf;
> > int *fixup_map_timer = test->fixup_map_timer;
> > int *fixup_map_kptr = test->fixup_map_kptr;
> > - struct kfunc_btf_id_pair *fixup_kfunc_btf_id = test->fixup_kfunc_btf_id;
> >
> > if (test->fill_helper) {
> > test->fill_insns = calloc(MAX_TEST_INSNS, sizeof(struct bpf_insn));
> > @@ -1106,25 +1237,7 @@ static void do_test_fixup(struct bpf_test *test, enum bpf_prog_type prog_type,
> > } while (*fixup_map_kptr);
> > }
> >
> > - /* Patch in kfunc BTF IDs */
> > - if (fixup_kfunc_btf_id->kfunc) {
> > - struct btf *btf;
> > - int btf_id;
> > -
> > - do {
> > - btf_id = 0;
> > - btf = btf__load_vmlinux_btf();
> > - if (btf) {
> > - btf_id = btf__find_by_name_kind(btf,
> > - fixup_kfunc_btf_id->kfunc,
> > - BTF_KIND_FUNC);
> > - btf_id = btf_id < 0 ? 0 : btf_id;
> > - }
> > - btf__free(btf);
> > - prog[fixup_kfunc_btf_id->insn_idx].imm = btf_id;
> > - fixup_kfunc_btf_id++;
> > - } while (fixup_kfunc_btf_id->kfunc);
> > - }
> > + fixup_prog_kfuncs(prog, fd_array, test->fixup_kfunc_btf_id);
> > }
> >
> > struct libcap {
> > @@ -1451,6 +1564,7 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
> > int run_errs, run_successes;
> > int map_fds[MAX_NR_MAPS];
> > const char *expected_err;
> > + int fd_array[2] = { -1, -1 };
> > int saved_errno;
> > int fixup_skips;
> > __u32 pflags;
> > @@ -1464,7 +1578,7 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
> > if (!prog_type)
> > prog_type = BPF_PROG_TYPE_SOCKET_FILTER;
> > fixup_skips = skips;
> > - do_test_fixup(test, prog_type, prog, map_fds);
> > + do_test_fixup(test, prog_type, prog, map_fds, &fd_array[1]);
> > if (test->fill_insns) {
> > prog = test->fill_insns;
> > prog_len = test->prog_len;
> > @@ -1498,6 +1612,8 @@ static void do_test_single(struct bpf_test *test, bool unpriv,
> > else
> > opts.log_level = DEFAULT_LIBBPF_LOG_LEVEL;
> > opts.prog_flags = pflags;
> > + if (fd_array[1] != -1)
> > + opts.fd_array = &fd_array[0];
> >
> > if ((prog_type == BPF_PROG_TYPE_TRACING ||
> > prog_type == BPF_PROG_TYPE_LSM) && test->kfunc) {
> > @@ -1740,6 +1856,7 @@ static int do_test(bool unpriv, unsigned int from, unsigned int to)
> > }
> >
> > unload_bpf_testmod(verbose);
> > + kfuncs_cleanup();
> >
> > printf("Summary: %d PASSED, %d SKIPPED, %d FAILED\n", passes,
> > skips, errors);
> > --
> > 2.39.1
> >