[PATCH 07/12] bpf: Return hashes of maps in BPF_OBJ_GET_INFO_BY_FD

[KP Singh]

Currently only array maps are supported, but the implementation can be
extended for other maps and objects. The hash is memoized only for
exclusive and frozen maps as their content is stable until the exclusive
program modifies the map.

This is required  for BPF signing, enabling a trusted loader program to
verify a map's integrity. The loader retrieves
the map's runtime hash from the kernel and compares it against an
expected hash computed at build time.

Signed-off-by: KP Singh <kpsingh at kernel.org>
---
 include/linux/bpf.h            |  3 +++
 include/uapi/linux/bpf.h       |  2 ++
 kernel/bpf/arraymap.c          | 13 ++++++++++++
 kernel/bpf/syscall.c           | 38 ++++++++++++++++++++++++++++++++++
 tools/include/uapi/linux/bpf.h |  2 ++
 5 files changed, 58 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index cb1bea99702a..35f1a633d87a 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -7,6 +7,7 @@
 #include <uapi/linux/bpf.h>
 #include <uapi/linux/filter.h>
 
+#include <crypto/sha2.h>
 #include <linux/workqueue.h>
 #include <linux/file.h>
 #include <linux/percpu.h>
@@ -110,6 +111,7 @@ struct bpf_map_ops {
 	long (*map_pop_elem)(struct bpf_map *map, void *value);
 	long (*map_peek_elem)(struct bpf_map *map, void *value);
 	void *(*map_lookup_percpu_elem)(struct bpf_map *map, void *key, u32 cpu);
+	int (*map_get_hash)(struct bpf_map *map, u32 hash_buf_size, void *hash_buf);
 
 	/* funcs called by prog_array and perf_event_array map */
 	void *(*map_fd_get_ptr)(struct bpf_map *map, struct file *map_file,
@@ -262,6 +264,7 @@ struct bpf_list_node_kern {
 } __attribute__((aligned(8)));
 
 struct bpf_map {
+	u8 sha[SHA256_DIGEST_SIZE];
 	const struct bpf_map_ops *ops;
 	struct bpf_map *inner_map_meta;
 #ifdef CONFIG_SECURITY
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 6f2f4f3b3822..ffd9e11befc2 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -6630,6 +6630,8 @@ struct bpf_map_info {
 	__u32 btf_value_type_id;
 	__u32 btf_vmlinux_id;
 	__u64 map_extra;
+	__aligned_u64 hash;
+	__u32 hash_size;
 } __attribute__((aligned(8)));
 
 struct bpf_btf_info {
diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
index 8719aa821b63..1fb989db03a2 100644
--- a/kernel/bpf/arraymap.c
+++ b/kernel/bpf/arraymap.c
@@ -12,6 +12,7 @@
 #include <uapi/linux/btf.h>
 #include <linux/rcupdate_trace.h>
 #include <linux/btf_ids.h>
+#include <crypto/sha256_base.h>
 
 #include "map_in_map.h"
 
@@ -174,6 +175,17 @@ static void *array_map_lookup_elem(struct bpf_map *map, void *key)
 	return array->value + (u64)array->elem_size * (index & array->index_mask);
 }
 
+static int array_map_get_hash(struct bpf_map *map, u32 hash_buf_size,
+			       void *hash_buf)
+{
+	struct bpf_array *array = container_of(map, struct bpf_array, map);
+
+	bpf_sha256(array->value, (u64)array->elem_size * array->map.max_entries,
+	       hash_buf);
+	memcpy(array->map.sha, hash_buf, sizeof(array->map.sha));
+	return 0;
+}
+
 static int array_map_direct_value_addr(const struct bpf_map *map, u64 *imm,
 				       u32 off)
 {
@@ -805,6 +817,7 @@ const struct bpf_map_ops array_map_ops = {
 	.map_mem_usage = array_map_mem_usage,
 	.map_btf_id = &array_map_btf_ids[0],
 	.iter_seq_info = &iter_seq_info,
+	.map_get_hash = &array_map_get_hash,
 };
 
 const struct bpf_map_ops percpu_array_map_ops = {
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index bef9edcfdb76..c81be07fa4fa 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0-only
 /* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
  */
+#include <crypto/sha2.h>
 #include <linux/bpf.h>
 #include <linux/bpf-cgroup.h>
 #include <linux/bpf_trace.h>
@@ -5027,6 +5028,9 @@ static int bpf_map_get_info_by_fd(struct file *file,
 	info_len = min_t(u32, sizeof(info), info_len);
 
 	memset(&info, 0, sizeof(info));
+	if (copy_from_user(&info, uinfo, info_len))
+		return -EFAULT;
+
 	info.type = map->map_type;
 	info.id = map->id;
 	info.key_size = map->key_size;
@@ -5051,6 +5055,40 @@ static int bpf_map_get_info_by_fd(struct file *file,
 			return err;
 	}
 
+	if (map->ops->map_get_hash && map->frozen && map->excl_prog_sha) {
+		err = map->ops->map_get_hash(map, SHA256_DIGEST_SIZE, &map->sha);
+		if (err != 0)
+			return err;
+	}
+
+	if (info.hash) {
+		char __user *uhash = u64_to_user_ptr(info.hash);
+
+		if (!map->ops->map_get_hash)
+			return -EINVAL;
+
+		if (info.hash_size < SHA256_DIGEST_SIZE)
+			return -EINVAL;
+
+		info.hash_size  = SHA256_DIGEST_SIZE;
+
+		if (map->excl_prog_sha && map->frozen) {
+			if (copy_to_user(uhash, map->sha, SHA256_DIGEST_SIZE) !=
+			    0)
+				return -EFAULT;
+		} else {
+			u8 sha[SHA256_DIGEST_SIZE];
+
+			err = map->ops->map_get_hash(map, SHA256_DIGEST_SIZE,
+						     sha);
+			if (err != 0)
+				return err;
+
+			if (copy_to_user(uhash, sha, SHA256_DIGEST_SIZE) != 0)
+				return -EFAULT;
+		}
+	}
+
 	if (copy_to_user(uinfo, &info, info_len) ||
 	    put_user(info_len, &uattr->info.info_len))
 		return -EFAULT;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 6f2f4f3b3822..ffd9e11befc2 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -6630,6 +6630,8 @@ struct bpf_map_info {
 	__u32 btf_value_type_id;
 	__u32 btf_vmlinux_id;
 	__u64 map_extra;
+	__aligned_u64 hash;
+	__u32 hash_size;
 } __attribute__((aligned(8)));
 
 struct bpf_btf_info {
-- 
2.43.0