[PATCH bpf-next 2/3] bpf: Add bpf_vma_build_id_parse helper

[Jiri Olsa <jolsa@kernel.org>]

Adding bpf_vma_build_id_parse helper that parses build ID of ELF file
mapped vma struct passed as an argument.

I originally wanted to add this as kfunc, but we need to be sure the
receiving buffer is big enough and we can't check for that on kfunc
side.

The use case for this helper is to provide the build id for executed
binaries on kernel side, when the monitoring user side does not have
access to the actual binaries.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 include/uapi/linux/bpf.h       |  9 +++++++++
 kernel/trace/bpf_trace.c       | 22 ++++++++++++++++++++++
 scripts/bpf_doc.py             |  2 ++
 tools/include/uapi/linux/bpf.h |  9 +++++++++
 4 files changed, 42 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 94659f6b3395..00559c40617e 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5481,6 +5481,14 @@ union bpf_attr {
  *		0 on success.
  *
  *		**-ENOENT** if the bpf_local_storage cannot be found.
+ *
+ * long bpf_vma_build_id_parse(struct vm_area_struct *vma, char *build_id)
+ *	Description
+ *		Parse build ID of ELF file mapped to @vma.
+ *
+ *	Return
+ *		Size of parsed build id on success.
+ *		Negative errno in case of failure.
  */
 #define ___BPF_FUNC_MAPPER(FN, ctx...)			\
 	FN(unspec, 0, ##ctx)				\
@@ -5695,6 +5703,7 @@ union bpf_attr {
 	FN(user_ringbuf_drain, 209, ##ctx)		\
 	FN(cgrp_storage_get, 210, ##ctx)		\
 	FN(cgrp_storage_delete, 211, ##ctx)		\
+	FN(vma_build_id_parse, 212, ##ctx)		\
 	/* */
 
 /* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index f2d8d070d024..b52d0f1b3c7a 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -23,6 +23,7 @@
 #include <linux/sort.h>
 #include <linux/key.h>
 #include <linux/verification.h>
+#include <linux/buildid.h>
 
 #include <net/bpf_sk_storage.h>
 
@@ -1205,6 +1206,25 @@ static const struct bpf_func_proto bpf_get_func_arg_cnt_proto = {
 	.arg1_type	= ARG_PTR_TO_CTX,
 };
 
+BPF_CALL_2(vma_build_id_parse, struct vm_area_struct *, vma, char *, build_id)
+{
+	__u32 size;
+	int err;
+
+	err = build_id_parse(vma, build_id, &size);
+	return err < 0 ? (long) err : (long) size;
+}
+
+static const struct bpf_func_proto bpf_vma_build_id_parse_proto = {
+	.func		= vma_build_id_parse,
+	.gpl_only	= false,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_PTR_TO_BTF_ID,
+	.arg1_btf_id	= &btf_tracing_ids[BTF_TRACING_TYPE_VMA],
+	.arg2_type	= ARG_PTR_TO_FIXED_SIZE_MEM,
+	.arg2_size	= BUILD_ID_SIZE_MAX,
+};
+
 #ifdef CONFIG_KEYS
 __diag_push();
 __diag_ignore_all("-Wmissing-prototypes",
@@ -1953,6 +1973,8 @@ tracing_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return bpf_prog_has_trampoline(prog) ? &bpf_get_func_arg_cnt_proto : NULL;
 	case BPF_FUNC_get_attach_cookie:
 		return bpf_prog_has_trampoline(prog) ? &bpf_get_attach_cookie_proto_tracing : NULL;
+	case BPF_FUNC_vma_build_id_parse:
+		return &bpf_vma_build_id_parse_proto;
 	default:
 		fn = raw_tp_prog_func_proto(func_id, prog);
 		if (!fn && prog->expected_attach_type == BPF_TRACE_ITER)
diff --git a/scripts/bpf_doc.py b/scripts/bpf_doc.py
index fdb0aff8cb5a..a55c3d0327db 100755
--- a/scripts/bpf_doc.py
+++ b/scripts/bpf_doc.py
@@ -700,6 +700,7 @@ class PrinterHelpers(Printer):
             'struct bpf_dynptr',
             'struct iphdr',
             'struct ipv6hdr',
+            'struct vm_area_struct',
     ]
     known_types = {
             '...',
@@ -754,6 +755,7 @@ class PrinterHelpers(Printer):
             'struct bpf_dynptr',
             'struct iphdr',
             'struct ipv6hdr',
+            'struct vm_area_struct',
     }
     mapped_types = {
             'u8': '__u8',
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 94659f6b3395..00559c40617e 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5481,6 +5481,14 @@ union bpf_attr {
  *		0 on success.
  *
  *		**-ENOENT** if the bpf_local_storage cannot be found.
+ *
+ * long bpf_vma_build_id_parse(struct vm_area_struct *vma, char *build_id)
+ *	Description
+ *		Parse build ID of ELF file mapped to @vma.
+ *
+ *	Return
+ *		Size of parsed build id on success.
+ *		Negative errno in case of failure.
  */
 #define ___BPF_FUNC_MAPPER(FN, ctx...)			\
 	FN(unspec, 0, ##ctx)				\
@@ -5695,6 +5703,7 @@ union bpf_attr {
 	FN(user_ringbuf_drain, 209, ##ctx)		\
 	FN(cgrp_storage_get, 210, ##ctx)		\
 	FN(cgrp_storage_delete, 211, ##ctx)		\
+	FN(vma_build_id_parse, 212, ##ctx)		\
 	/* */
 
 /* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't
-- 
2.38.1