Messages in this thread Patch in this message | | | Date | Mon, 21 Aug 2023 10:48:06 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | [PATCH] perf bpf augmented_raw_syscalls: Add an assert to make sure sizeof(saddr) is a power of two. |
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We're using the BPF verifier suggestion:
22: (85) call bpf_probe_read#4 R2 min value is negative, either use unsigned or 'var &= const'
That works only when const is a (power of two - 1) so add an assert to make sure that that is the case.
Suggested-by: Ian Rogers <irogers@google.com> Cc: Adrian Hunter <adrian.hunter@intel.com> Cc: Jiri Olsa <jolsa@kernel.org> Cc: Namhyung Kim <namhyung@kernel.org> Link: https://lore.kernel.org/lkml/ Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> --- tools/perf/util/bpf_skel/augmented_raw_syscalls.bpf.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
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); -- 2.37.1
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