Re: [PATCH 1/1] perf bpf_skel augmented_raw_syscalls: Cap the socklen parameter using &= sizeof(saddr)

[Ian Rogers]

On Mon, Aug 21, 2023 at 6:40 AM Arnaldo Carvalho de Melo
<acme@xxxxxxxxxx> 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@xxxxxxxxxx> 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@toolbox 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@toolbox 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@toolbox perf-tools-next]$
>
>
>
>