[net-next,2/3,v3] bpf: change helper bpf_probe_read arg2 type to ARG_CONST_SIZE_OR_ZERO

Message ID 20171112224911.2403770-3-yhs@fb.com
State Accepted
Delegated to: David Miller
Headers show
Series
  • bpf: improve verifier ARG_CONST_SIZE_OR_ZERO semantics
Related show

Commit Message

Yonghong Song Nov. 12, 2017, 10:49 p.m.
The helper bpf_probe_read arg2 type is changed
from ARG_CONST_SIZE to ARG_CONST_SIZE_OR_ZERO to permit
size-0 buffer. Together with newer ARG_CONST_SIZE_OR_ZERO
semantics which allows non-NULL buffer with size 0,
this allows simpler bpf programs with verifier acceptance.
The previous commit which changes ARG_CONST_SIZE_OR_ZERO semantics
has details on examples.

Signed-off-by: Yonghong Song <yhs@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
---
 kernel/trace/bpf_trace.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

Patch

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 506efe6..a5580c6 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -78,12 +78,16 @@  EXPORT_SYMBOL_GPL(trace_call_bpf);
 
 BPF_CALL_3(bpf_probe_read, void *, dst, u32, size, const void *, unsafe_ptr)
 {
-	int ret;
+	int ret = 0;
+
+	if (unlikely(size == 0))
+		goto out;
 
 	ret = probe_kernel_read(dst, unsafe_ptr, size);
 	if (unlikely(ret < 0))
 		memset(dst, 0, size);
 
+ out:
 	return ret;
 }
 
@@ -92,7 +96,7 @@  static const struct bpf_func_proto bpf_probe_read_proto = {
 	.gpl_only	= true,
 	.ret_type	= RET_INTEGER,
 	.arg1_type	= ARG_PTR_TO_UNINIT_MEM,
-	.arg2_type	= ARG_CONST_SIZE,
+	.arg2_type	= ARG_CONST_SIZE_OR_ZERO,
 	.arg3_type	= ARG_ANYTHING,
 };