perf augmented_syscalls: Check probe_read_str() return separately (21d7eb9a) · Commits · 戴 / test

Using a value returned from probe_read_str() to tell how many bytes to copy using perf_event_output() has issues in some older kernels, like 4.17.17-100.fc27.x86_64, so separate the bounds checking done on how many bytes to copy to a separate variable, so that the next patch has only what is being done to make the test pass on older BPF validators. For reference, see the discussion in this thread: https://www.spinics.net/lists/netdev/msg480099.html Cc: Adrian Hunter <adrian.hunter@intel.com> Cc: Daniel Borkmann <daniel@iogearbox.net> Cc: David Ahern <dsahern@gmail.com> Cc: Jiri Olsa <jolsa@kernel.org> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Wang Nan <wangnan0@huawei.com> Cc: Yonghong Song <yhs@fb.com> Link: https://lkml.kernel.org/n/tip-jtsapwibyxrnv1xjfsgzp0fj@git.kernel.org Signed-off-by:

Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/examples/bpf/augmented_syscalls.c

+7 −6

Original line number	Diff line number	Diff line
		@@ -33,7 +33,7 @@ struct syscall_exit_args {
		};

		struct augmented_filename {
		int size;
		unsigned int size;
		int reserved;
		char value[256];
		};
		@@ -46,14 +46,15 @@ struct augmented_enter_##syscall##_args { \
		int syscall_enter(syscall)(struct syscall_enter_##syscall##_args *args) \
		{ \
		struct augmented_enter_##syscall##_args augmented_args = { .filename.reserved = 0, }; \
		unsigned int len = sizeof(augmented_args); \
		probe_read(&augmented_args.args, sizeof(augmented_args.args), args); \
		augmented_args.filename.size = probe_read_str(&augmented_args.filename.value, \
		sizeof(augmented_args.filename.value), \
		args->filename_ptr); \
		if (augmented_args.filename.size < sizeof(augmented_args.filename.value)) \
		len -= sizeof(augmented_args.filename.value) - augmented_args.filename.size; \
		perf_event_output(args, &__augmented_syscalls__, BPF_F_CURRENT_CPU, \
		&augmented_args, \
		(sizeof(augmented_args) - sizeof(augmented_args.filename.value) + \
		augmented_args.filename.size)); \
		&augmented_args, len); \
		return 0; \
		} \
		int syscall_exit(syscall)(struct syscall_exit_args *args) \

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