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Message-ID: <ZOT5mK2MgQXTx75w@kernel.org>
Date: Tue, 22 Aug 2023 15:08:24 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Adrian Hunter <adrian.hunter@...el.com>,
Jiri Olsa <jolsa@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] perf bpf_skel augmented_raw_syscalls: Cap the
socklen parameter using &= sizeof(saddr)
Em Mon, Aug 21, 2023 at 07:52:46AM -0700, Ian Rogers escreveu:
> On Mon, Aug 21, 2023 at 6:40 AM Arnaldo Carvalho de Melo
> <acme@...nel.org> wrote:
> >
> > Em Wed, Aug 16, 2023 at 03:10:00PM -0700, Ian Rogers escreveu:
> > > On Wed, Aug 16, 2023 at 2:48 PM Arnaldo Carvalho de Melo <acme@...nel.org> wrote:
> > > > R2 min value is negative, either use unsigned or 'var &= const'
> > > > processed 22 insns (limit 1000000) max_states_per_insn 0 total_states 1 peak_states 1 mark_read 1
> > > > -- END PROG LOAD LOG --
> > > > libbpf: prog 'sys_enter_sendto': failed to load: -13
> > > > libbpf: failed to load object 'augmented_raw_syscalls_bpf'
> > > > libbpf: failed to load BPF skeleton 'augmented_raw_syscalls_bpf': -13
> > > >
> > > > So use the suggested &= variant since sizeof(saddr) == 128 bytes.
> > >
> > > Could this be an assert?
> >
> > you mean (removing the change to saddr to make it trigger):
>
> I was more meaning that doing sizeof(x) -1 and assuming that x is a
> power of two should really have an assert that sizeof(x) is a power of
Right, that was my understanding, and that is what:
_Static_assert(is_power_of_2(sizeof(augmented_args->saddr)), "sizeof(augmented_args->saddr) needs to be a power of two")
Does, right?
- Arnaldo
> 2. Using 127 and asserting sizeof(x)==128 also works.
> Thanks,
> Ian
>
> > diff --git a/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c b/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
> > index 9c1d0b271b20f693..521ce2d7357d983c 100644
> > --- a/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
> > +++ b/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
> > @@ -10,6 +10,16 @@
> > #include <bpf/bpf_helpers.h>
> > #include <linux/limits.h>
> >
> > +/**
> > + * is_power_of_2() - check if a value is a power of two
> > + * @n: the value to check
> > + *
> > + * Determine whether some value is a power of two, where zero is *not*
> > + * considered a power of two. Return: true if @n is a power of 2, otherwise
> > + * false.
> > + */
> > +#define is_power_of_2(n) (n != 0 && ((n & (n - 1)) == 0))
> > +
> > #define MAX_CPUS 4096
> >
> > // FIXME: These should come from system headers
> > @@ -112,7 +122,10 @@ struct augmented_args_payload {
> > struct {
> > struct augmented_arg arg, arg2;
> > };
> > - struct sockaddr_storage saddr;
> > + struct {
> > + struct sockaddr_storage real_saddr;
> > + char padding;
> > + } saddr;
> > char __data[sizeof(struct augmented_arg)];
> > };
> > };
> > @@ -187,6 +200,7 @@ int sys_enter_connect(struct syscall_enter_args *args)
> > if (augmented_args == NULL)
> > return 1; /* Failure: don't filter */
> >
> > + _Static_assert(is_power_of_2(sizeof(augmented_args->saddr)), "sizeof(augmented_args->saddr) needs to be a power of two");
> > socklen &= sizeof(augmented_args->saddr) - 1;
> >
> > bpf_probe_read(&augmented_args->saddr, socklen, sockaddr_arg);
> >
> >
> > --------------------------------
> >
> > CLANG /tmp/build/perf-tools-next/util/bpf_skel/.tmp/augmented_raw_syscalls.bpf.o
> > util/bpf_skel/augmented_raw_syscalls.bpf.c:203:2: error: static_assert failed due to requirement 'sizeof (augmented_args->saddr) != 0 && ((sizeof (augmented_args->saddr) & (sizeof (augmented_args->saddr) - 1)) == 0)' "sizeof(augmented_args->saddr) needs to be a power of two"
> > _Static_assert(is_power_of_2(sizeof(augmented_args->saddr)), "sizeof(augmented_args->saddr) needs to be a power of two");
> > ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > 1 error generated.
> > make[2]: *** [Makefile.perf:1104: /tmp/build/perf-tools-next/util/bpf_skel/.tmp/augmented_raw_syscalls.bpf.o] Error 1
> > make[1]: *** [Makefile.perf:238: sub-make] Error 2
> > make: *** [Makefile:113: install-bin] Error 2
> > make: Leaving directory '/var/home/acme/git/perf-tools-next/tools/perf'
> >
> > And here the assert being satisfied:
> >
> > ⬢[acme@...lbox perf-tools-next]$ git diff
> > diff --git a/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c b/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
> > index 9c1d0b271b20f693..43549b63b433d81e 100644
> > --- a/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
> > +++ b/tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c
> > @@ -10,6 +10,16 @@
> > #include <bpf/bpf_helpers.h>
> > #include <linux/limits.h>
> >
> > +/**
> > + * is_power_of_2() - check if a value is a power of two
> > + * @n: the value to check
> > + *
> > + * Determine whether some value is a power of two, where zero is *not*
> > + * considered a power of two. Return: true if @n is a power of 2, otherwise
> > + * false.
> > + */
> > +#define is_power_of_2(n) (n != 0 && ((n & (n - 1)) == 0))
> > +
> > #define MAX_CPUS 4096
> >
> > // FIXME: These should come from system headers
> > @@ -187,6 +197,7 @@ int sys_enter_connect(struct syscall_enter_args *args)
> > if (augmented_args == NULL)
> > return 1; /* Failure: don't filter */
> >
> > + _Static_assert(is_power_of_2(sizeof(augmented_args->saddr)), "sizeof(augmented_args->saddr) needs to be a power of two");
> > socklen &= sizeof(augmented_args->saddr) - 1;
> >
> > bpf_probe_read(&augmented_args->saddr, socklen, sockaddr_arg);
> > ⬢[acme@...lbox perf-tools-next]$ m
> > make: Entering directory '/var/home/acme/git/perf-tools-next/tools/perf'
> > BUILD: Doing 'make -j32' parallel build
> > INSTALL libsubcmd_headers
> > INSTALL libperf_headers
> > INSTALL libapi_headers
> > INSTALL libbpf_headers
> > CLANG /tmp/build/perf-tools-next/util/bpf_skel/.tmp/augmented_raw_syscalls.bpf.o
> > GENSKEL /tmp/build/perf-tools-next/util/bpf_skel/augmented_raw_syscalls.skel.h
> > INSTALL libsymbol_headers
> > CC /tmp/build/perf-tools-next/builtin-trace.o
> > LD /tmp/build/perf-tools-next/perf-in.o
> > LINK /tmp/build/perf-tools-next/perf
> > INSTALL binaries
> > INSTALL tests
> > INSTALL libperf-jvmti.so
> > INSTALL libexec
> > INSTALL perf-archive
> > INSTALL perf-iostat
> > INSTALL strace/groups
> > INSTALL perl-scripts
> > INSTALL python-scripts
> > INSTALL dlfilters
> > INSTALL perf_completion-script
> > INSTALL perf-tip
> > make: Leaving directory '/var/home/acme/git/perf-tools-next/tools/perf'
> > ⬢[acme@...lbox perf-tools-next]$
> >
> >
> >
> >
--
- Arnaldo
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