On Fri, 1 Nov 2024 at 14:19, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Thu, Oct 31, 2024 at 5:00 PM Kumar Kartikeya Dwivedi
> <memxor@xxxxxxxxx> wrote:
> >
> > Ensure that trusted PTR_TO_BTF_ID accesses perform PROBE_MEM handling in
> > raw_tp program. Without the previous fix, this selftest crashes the
> > kernel due to a NULL-pointer dereference. Also ensure that dead code
> > elimination does not kick in for checks on the pointer.
> >
> > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> > ---
> > .../bpf/bpf_testmod/bpf_testmod-events.h | 8 ++++++
> > .../selftests/bpf/bpf_testmod/bpf_testmod.c | 2 ++
> > .../selftests/bpf/prog_tests/raw_tp_null.c | 25 +++++++++++++++++
> > .../testing/selftests/bpf/progs/raw_tp_null.c | 27 +++++++++++++++++++
> > 4 files changed, 62 insertions(+)
> > create mode 100644 tools/testing/selftests/bpf/prog_tests/raw_tp_null.c
> > create mode 100644 tools/testing/selftests/bpf/progs/raw_tp_null.c
> >
> > diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h
> > index 6c3b4d4f173a..aeef86b3da74 100644
> > --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h
> > +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod-events.h
> > @@ -40,6 +40,14 @@ DECLARE_TRACE(bpf_testmod_test_nullable_bare,
> > TP_ARGS(ctx__nullable)
> > );
> >
> > +struct sk_buff;
> > +
> > +DECLARE_TRACE(bpf_testmod_test_raw_tp_null,
> > + TP_PROTO(struct sk_buff *skb),
> > + TP_ARGS(skb)
> > +);
> > +
> > +
> > #undef BPF_TESTMOD_DECLARE_TRACE
> > #ifdef DECLARE_TRACE_WRITABLE
> > #define BPF_TESTMOD_DECLARE_TRACE(call, proto, args, size) \
> > diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > index 8835761d9a12..4e6a9e9c0368 100644
> > --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> > @@ -380,6 +380,8 @@ bpf_testmod_test_read(struct file *file, struct kobject *kobj,
> >
> > (void)bpf_testmod_test_arg_ptr_to_struct(&struct_arg1_2);
> >
> > + (void)trace_bpf_testmod_test_raw_tp_null(NULL);
> > +
> > struct_arg3 = kmalloc((sizeof(struct bpf_testmod_struct_arg_3) +
> > sizeof(int)), GFP_KERNEL);
> > if (struct_arg3 != NULL) {
> > diff --git a/tools/testing/selftests/bpf/prog_tests/raw_tp_null.c b/tools/testing/selftests/bpf/prog_tests/raw_tp_null.c
> > new file mode 100644
> > index 000000000000..b9068fee7d8a
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/prog_tests/raw_tp_null.c
> > @@ -0,0 +1,25 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
> > +
> > +#include <test_progs.h>
> > +#include "raw_tp_null.skel.h"
> > +
> > +void test_raw_tp_null(void)
> > +{
> > + struct raw_tp_null *skel;
> > +
> > + skel = raw_tp_null__open_and_load();
> > + if (!ASSERT_OK_PTR(skel, "raw_tp_null__open_and_load"))
> > + return;
> > +
> > + skel->bss->tid = gettid();
>
> this is not available everywhere, we just recently had a fix. Other
> tests call syscall() directly. It might be time to add macro in one of
> the helpers headers, though. But that can be done as a separate clean
> up patch outside of this change (there is enough to review and
> discuss)
Ok, I can include a clean up patch in the next revision.
>
> > +
> > + if (!ASSERT_OK(raw_tp_null__attach(skel), "raw_tp_null__attach"))
> > + goto end;
> > +
> > + ASSERT_OK(trigger_module_test_read(2), "trigger testmod read");
> > + ASSERT_EQ(skel->bss->i, 3, "invocations");
> > +
> > +end:
> > + raw_tp_null__destroy(skel);
> > +}
> > diff --git a/tools/testing/selftests/bpf/progs/raw_tp_null.c b/tools/testing/selftests/bpf/progs/raw_tp_null.c
> > new file mode 100644
> > index 000000000000..c7c9ad4ec3b7
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/progs/raw_tp_null.c
> > @@ -0,0 +1,27 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/* Copyright (c) 2024 Meta Platforms, Inc. and affiliates. */
> > +
> > +#include <vmlinux.h>
> > +#include <bpf/bpf_tracing.h>
> > +
> > +char _license[] SEC("license") = "GPL";
> > +
> > +int tid;
> > +int i;
> > +
> > +SEC("tp_btf/bpf_testmod_test_raw_tp_null")
> > +int BPF_PROG(test_raw_tp_null, struct sk_buff *skb)
> > +{
> > + if (bpf_get_current_task_btf()->pid == tid) {
>
> nit: avoid unnecessary nesting. Check condition and return early. Also
> seems nicer to have task_struct local variable for this, tbh:
>
> struct task_struct *t = bpf_get_current_task_btf();
>
> if (t->pid != tid)
> return 0;
>
> /* the rest follows, unnested */
Ack.
>
> > + i = i + skb->mark + 1;
> > +
> > + /* If dead code elimination kicks in, the increment below will
> > + * be removed. For raw_tp programs, we mark input arguments as
> > + * PTR_MAYBE_NULL, so branch prediction should never kick in.
> > + */
> > + if (!skb)
> > + i += 2;
> > + }
> > +
> > + return 0;
> > +}
> > --
> > 2.43.5
> >
