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bpf: add writable context for raw tracepoints

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This is an opt-in interface that allows a tracepoint to provide a safe
buffer that can be written from a BPF_PROG_TYPE_RAW_TRACEPOINT program.
The size of the buffer must be a compile-time constant, and is checked
before allowing a BPF program to attach to a tracepoint that uses this
feature.

The pointer to this buffer will be the first argument of tracepoints
that opt in; the pointer is valid and can be bpf_probe_read() by both
BPF_PROG_TYPE_RAW_TRACEPOINT and BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE
programs that attach to such a tracepoint, but the buffer to which it
points may only be written by the latter.

Signed-off-by: Matt Mullins <mmullins@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Matt Mullins
2019-04-26 11:49:47 -07:00
committed by Alexei Starovoitov
parent 34b8ab091f
commit 9df1c28bb7
8 changed files with 91 additions and 4 deletions
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27
include/trace/bpf_probe.h
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@@ -69,8 +69,7 @@ __bpf_trace_##call(void *__data, proto) \
* to make sure that if the tracepoint handling changes, the
* bpf probe will fail to compile unless it too is updated.
*/
#undef DEFINE_EVENT
#define DEFINE_EVENT(template, call, proto, args) \
#define __DEFINE_EVENT(template, call, proto, args, size) \
static inline void bpf_test_probe_##call(void) \
{ \
check_trace_callback_type_##call(__bpf_trace_##template); \
@@ -81,12 +80,36 @@ __bpf_trace_tp_map_##call = { \
.tp = &__tracepoint_##call, \
.bpf_func = (void *)__bpf_trace_##template, \
.num_args = COUNT_ARGS(args), \
.writable_size = size, \
};
#define FIRST(x, ...) x
#undef DEFINE_EVENT_WRITABLE
#define DEFINE_EVENT_WRITABLE(template, call, proto, args, size) \
static inline void bpf_test_buffer_##call(void) \
{ \
/* BUILD_BUG_ON() is ignored if the code is completely eliminated, but \
* BUILD_BUG_ON_ZERO() uses a different mechanism that is not \
* dead-code-eliminated. \
*/ \
FIRST(proto); \
(void)BUILD_BUG_ON_ZERO(size != sizeof(*FIRST(args))); \
} \
__DEFINE_EVENT(template, call, PARAMS(proto), PARAMS(args), size)
#undef DEFINE_EVENT
#define DEFINE_EVENT(template, call, proto, args) \
__DEFINE_EVENT(template, call, PARAMS(proto), PARAMS(args), 0)
#undef DEFINE_EVENT_PRINT
#define DEFINE_EVENT_PRINT(template, name, proto, args, print) \
DEFINE_EVENT(template, name, PARAMS(proto), PARAMS(args))
#include TRACE_INCLUDE(TRACE_INCLUDE_FILE)
#undef DEFINE_EVENT_WRITABLE
#undef __DEFINE_EVENT
#undef FIRST
#endif /* CONFIG_BPF_EVENTS */