Re: [PATCH 02/13] kprobe: Keep traced function address

Jiri Olsa
2022-01-06T08:30:53Z

On Wed, Jan 05, 2022 at 11:32:52PM +0900, Masami Hiramatsu wrote:
> On Tue, 4 Jan 2022 09:09:32 +0100
> Jiri Olsa <jolsa@redhat.com> wrote:
>
> > The bpf_get_func_ip_kprobe helper should return traced function
> > address, but it's doing so only for kprobes that are placed on
> > the function entry.
> >
> > If kprobe is placed within the function, bpf_get_func_ip_kprobe
> > returns that address instead of function entry.
> >
> > Storing the function entry directly in kprobe object, so it could
> > be used in bpf_get_func_ip_kprobe helper.
>
> Hmm, please do this in bpf side, which should have some data structure
> around the kprobe itself. Do not add this "specialized" field to
> the kprobe data structure.

ok, will check

thanks,
jirka

>
> Thank you,
>
> >
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> > include/linux/kprobes.h | 3 +++
> > kernel/kprobes.c | 12 ++++++++++++
> > kernel/trace/bpf_trace.c | 2 +-
> > tools/testing/selftests/bpf/progs/get_func_ip_test.c | 4 ++--
> > 4 files changed, 18 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> > index 8c8f7a4d93af..a204df4fef96 100644
> > --- a/include/linux/kprobes.h
> > +++ b/include/linux/kprobes.h
> > @@ -74,6 +74,9 @@ struct kprobe {
> > /* Offset into the symbol */
> > unsigned int offset;
> >
> > + /* traced function address */
> > + unsigned long func_addr;
> > +
> > /* Called before addr is executed. */
> > kprobe_pre_handler_t pre_handler;
> >
> > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> > index d20ae8232835..c4060a8da050 100644
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -1310,6 +1310,7 @@ static void init_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
> > copy_kprobe(p, ap);
> > flush_insn_slot(ap);
> > ap->addr = p->addr;
> > + ap->func_addr = p->func_addr;
> > ap->flags = p->flags & ~KPROBE_FLAG_OPTIMIZED;
> > ap->pre_handler = aggr_pre_handler;
> > /* We don't care the kprobe which has gone. */
> > @@ -1588,6 +1589,16 @@ static int check_kprobe_address_safe(struct kprobe *p,
> > return ret;
> > }
> >
> > +static unsigned long resolve_func_addr(kprobe_opcode_t *addr)
> > +{
> > + char str[KSYM_SYMBOL_LEN];
> > + unsigned long offset;
> > +
> > + if (kallsyms_lookup((unsigned long) addr, NULL, &offset, NULL, str))
> > + return (unsigned long) addr - offset;
> > + return 0;
> > +}
> > +
> > int register_kprobe(struct kprobe *p)
> > {
> > int ret;
> > @@ -1600,6 +1611,7 @@ int register_kprobe(struct kprobe *p)
> > if (IS_ERR(addr))
> > return PTR_ERR(addr);
> > p->addr = addr;
> > + p->func_addr = resolve_func_addr(addr);
> >
> > ret = warn_kprobe_rereg(p);
> > if (ret)
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index 21aa30644219..25631253084a 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -1026,7 +1026,7 @@ BPF_CALL_1(bpf_get_func_ip_kprobe, struct pt_regs *, regs)
> > {
> > struct kprobe *kp = kprobe_running();
> >
> > - return kp ? (uintptr_t)kp->addr : 0;
> > + return kp ? (uintptr_t)kp->func_addr : 0;
> > }
> >
> > static const struct bpf_func_proto bpf_get_func_ip_proto_kprobe = {
> > diff --git a/tools/testing/selftests/bpf/progs/get_func_ip_test.c b/tools/testing/selftests/bpf/progs/get_func_ip_test.c
> > index a587aeca5ae0..e988aefa567e 100644
> > --- a/tools/testing/selftests/bpf/progs/get_func_ip_test.c
> > +++ b/tools/testing/selftests/bpf/progs/get_func_ip_test.c
> > @@ -69,7 +69,7 @@ int test6(struct pt_regs *ctx)
> > {
> > __u64 addr = bpf_get_func_ip(ctx);
> >
> > - test6_result = (const void *) addr == &bpf_fentry_test6 + 5;
> > + test6_result = (const void *) addr == &bpf_fentry_test6;
> > return 0;
> > }
> >
> > @@ -79,6 +79,6 @@ int test7(struct pt_regs *ctx)
> > {
> > __u64 addr = bpf_get_func_ip(ctx);
> >
> > - test7_result = (const void *) addr == &bpf_fentry_test7 + 5;
> > + test7_result = (const void *) addr == &bpf_fentry_test7;
> > return 0;
> > }
> > --
> > 2.33.1
> >
>
>
> --
> Masami Hiramatsu <mhiramat@kernel.org>
>