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Date: Mon, 21 Aug 2023 07:52:46 -0700
From: Ian Rogers <irogers@...gle.com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
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)
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
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]$
>
>
>
>
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