[PATCH net] trace/bpf: remove helper bpf_perf_prog_read_value from tracepoint type programs

[PATCH net] trace/bpf: remove helper bpf_perf_prog_read_value from tracepoint type programs

[Yonghong Song]

Commit 4bebdc7a85aa ("bpf: add helper bpf_perf_prog_read_value")
added helper bpf_perf_prog_read_value so that perf_event type program
can read event counter and enabled/running time.
This commit, however, introduced a bug which allows this helper
for tracepoint type programs. This is incorrect as bpf_perf_prog_read_value
needs to access perf_event through its bpf_perf_event_data_kern type context,
which is not available for tracepoint type program.

This patch fixed the issue by separating bpf_func_proto between tracepoint
and perf_event type programs and removed bpf_perf_prog_read_value
from tracepoint func prototype.

Fixes: Commit 4bebdc7a85aa ("bpf: add helper bpf_perf_prog_read_value")
Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
---
 kernel/trace/bpf_trace.c | 68 ++++++++++++++++++++++++++++--------------------
 1 file changed, 40 insertions(+), 28 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index c634e09..7f9691c 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -661,7 +661,41 @@ static const struct bpf_func_proto bpf_get_stackid_proto_tp = {
 	.arg3_type	= ARG_ANYTHING,
 };
 
-BPF_CALL_3(bpf_perf_prog_read_value_tp, struct bpf_perf_event_data_kern *, ctx,
+static const struct bpf_func_proto *tp_prog_func_proto(enum bpf_func_id func_id)
+{
+	switch (func_id) {
+	case BPF_FUNC_perf_event_output:
+		return &bpf_perf_event_output_proto_tp;
+	case BPF_FUNC_get_stackid:
+		return &bpf_get_stackid_proto_tp;
+	default:
+		return tracing_func_proto(func_id);
+	}
+}
+
+static bool tp_prog_is_valid_access(int off, int size, enum bpf_access_type type,
+				    struct bpf_insn_access_aux *info)
+{
+	if (off < sizeof(void *) || off >= PERF_MAX_TRACE_SIZE)
+		return false;
+	if (type != BPF_READ)
+		return false;
+	if (off % size != 0)
+		return false;
+
+	BUILD_BUG_ON(PERF_MAX_TRACE_SIZE % sizeof(__u64));
+	return true;
+}
+
+const struct bpf_verifier_ops tracepoint_verifier_ops = {
+	.get_func_proto  = tp_prog_func_proto,
+	.is_valid_access = tp_prog_is_valid_access,
+};
+
+const struct bpf_prog_ops tracepoint_prog_ops = {
+};
+
+BPF_CALL_3(bpf_perf_prog_read_value, struct bpf_perf_event_data_kern *, ctx,
 	   struct bpf_perf_event_value *, buf, u32, size)
 {
 	int err = -EINVAL;
@@ -678,8 +712,8 @@ BPF_CALL_3(bpf_perf_prog_read_value_tp, struct bpf_perf_event_data_kern *, ctx,
 	return err;
 }
 
-static const struct bpf_func_proto bpf_perf_prog_read_value_proto_tp = {
-         .func           = bpf_perf_prog_read_value_tp,
+static const struct bpf_func_proto bpf_perf_prog_read_value_proto = {
+         .func           = bpf_perf_prog_read_value,
          .gpl_only       = true,
          .ret_type       = RET_INTEGER,
          .arg1_type      = ARG_PTR_TO_CTX,
@@ -687,7 +721,7 @@ static const struct bpf_func_proto bpf_perf_prog_read_value_proto_tp = {
          .arg3_type      = ARG_CONST_SIZE,
 };
 
-static const struct bpf_func_proto *tp_prog_func_proto(enum bpf_func_id func_id)
+static const struct bpf_func_proto *pe_prog_func_proto(enum bpf_func_id func_id)
 {
 	switch (func_id) {
 	case BPF_FUNC_perf_event_output:
@@ -695,34 +729,12 @@ static const struct bpf_func_proto *tp_prog_func_proto(enum bpf_func_id func_id)
 	case BPF_FUNC_get_stackid:
 		return &bpf_get_stackid_proto_tp;
 	case BPF_FUNC_perf_prog_read_value:
-		return &bpf_perf_prog_read_value_proto_tp;
+		return &bpf_perf_prog_read_value_proto;
 	default:
 		return tracing_func_proto(func_id);
 	}
 }
 
-static bool tp_prog_is_valid_access(int off, int size, enum bpf_access_type type,
-				    struct bpf_insn_access_aux *info)
-{
-	if (off < sizeof(void *) || off >= PERF_MAX_TRACE_SIZE)
-		return false;
-	if (type != BPF_READ)
-		return false;
-	if (off % size != 0)
-		return false;
-
-	BUILD_BUG_ON(PERF_MAX_TRACE_SIZE % sizeof(__u64));
-	return true;
-}
-
-const struct bpf_verifier_ops tracepoint_verifier_ops = {
-	.get_func_proto  = tp_prog_func_proto,
-	.is_valid_access = tp_prog_is_valid_access,
-};
-
-const struct bpf_prog_ops tracepoint_prog_ops = {
-};
-
 static bool pe_prog_is_valid_access(int off, int size, enum bpf_access_type type,
 				    struct bpf_insn_access_aux *info)
 {
@@ -791,7 +803,7 @@ static u32 pe_prog_convert_ctx_access(enum bpf_access_type type,
 }
 
 const struct bpf_verifier_ops perf_event_verifier_ops = {
-	.get_func_proto		= tp_prog_func_proto,
+	.get_func_proto		= pe_prog_func_proto,
 	.is_valid_access	= pe_prog_is_valid_access,
 	.convert_ctx_access	= pe_prog_convert_ctx_access,
 };
-- 
2.9.5

Re: [PATCH net] trace/bpf: remove helper bpf_perf_prog_read_value from tracepoint type programs

[Daniel Borkmann]

On 03/20/2018 07:19 PM, Yonghong Song wrote:
> Commit 4bebdc7a85aa ("bpf: add helper bpf_perf_prog_read_value")
> added helper bpf_perf_prog_read_value so that perf_event type program
> can read event counter and enabled/running time.
> This commit, however, introduced a bug which allows this helper
> for tracepoint type programs. This is incorrect as bpf_perf_prog_read_value
> needs to access perf_event through its bpf_perf_event_data_kern type context,
> which is not available for tracepoint type program.
> 
> This patch fixed the issue by separating bpf_func_proto between tracepoint
> and perf_event type programs and removed bpf_perf_prog_read_value
> from tracepoint func prototype.
> 
> Fixes: Commit 4bebdc7a85aa ("bpf: add helper bpf_perf_prog_read_value")
> Reported-by: Alexei Starovoitov <ast@kernel.org>
> Signed-off-by: Yonghong Song <yhs@fb.com>

Sigh, also makes sense to split given this is so subtle. Applied to bpf,
thanks Yonghong!