[PATCHv2 bpf-next 1/2] bpf: Add bpf_vma_build_id_parse function and kfunc

[Jiri Olsa <jolsa@kernel.org>]

Adding bpf_vma_build_id_parse function to retrieve build id from
passed vma object and making it available as bpf kfunc.

We can't use build_id_parse directly as kfunc, because we would
not have control over the build id buffer size provided by user.

Instead we are adding new bpf_vma_build_id_parse function with
'build_id__sz' argument that instructs verifier to check for the
available space in build_id buffer.

This way  we check that there's  always available memory space
behind build_id pointer. We also check that the build_id__sz is
at least BUILD_ID_SIZE_MAX so we can place any buildid in.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 include/linux/bpf.h  |  5 +++++
 kernel/bpf/helpers.c | 16 ++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 798aec816970..5e7c4c50da8e 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2779,4 +2779,9 @@ struct bpf_key {
 	bool has_ref;
 };
 #endif /* CONFIG_KEYS */
+
+extern int bpf_vma_build_id_parse(struct vm_area_struct *vma,
+				  unsigned char *build_id,
+				  size_t build_id__sz);
+
 #endif /* _LINUX_BPF_H */
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 283f55bbeb70..af7a30dafff3 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -19,6 +19,7 @@
 #include <linux/proc_ns.h>
 #include <linux/security.h>
 #include <linux/btf_ids.h>
+#include <linux/buildid.h>
 
 #include "../../lib/kstrtox.h"
 
@@ -1706,10 +1707,25 @@ bpf_base_func_proto(enum bpf_func_id func_id)
 	}
 }
 
+int bpf_vma_build_id_parse(struct vm_area_struct *vma,
+			   unsigned char *build_id,
+			   size_t build_id__sz)
+{
+	__u32 size;
+	int err;
+
+	if (build_id__sz < BUILD_ID_SIZE_MAX)
+		return -EINVAL;
+
+	err = build_id_parse(vma, build_id, &size);
+	return err ?: (int) size;
+}
+
 BTF_SET8_START(tracing_btf_ids)
 #ifdef CONFIG_KEXEC_CORE
 BTF_ID_FLAGS(func, crash_kexec, KF_DESTRUCTIVE)
 #endif
+BTF_ID_FLAGS(func, bpf_vma_build_id_parse)
 BTF_SET8_END(tracing_btf_ids)
 
 static const struct btf_kfunc_id_set tracing_kfunc_set = {
-- 
2.38.1