[PATCH 01/12] bpf: Implement an internal helper for SHA256 hashing

[KP Singh <kpsingh@kernel.org>]

This patch introduces bpf_sha256, an internal helper function
that wraps the standard kernel crypto API to compute SHA256 digests of
the program insns and map content

Signed-off-by: KP Singh <kpsingh@kernel.org>
---
 include/linux/bpf.h |  1 +
 kernel/bpf/core.c   | 39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 5b25d278409b..d5ae43b36e68 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2086,6 +2086,7 @@ static inline bool map_type_contains_progs(struct bpf_map *map)
 }
 
 bool bpf_prog_map_compatible(struct bpf_map *map, const struct bpf_prog *fp);
+int bpf_sha256(u8 *data, size_t data_size, u8 *output_digest);
 int bpf_prog_calc_tag(struct bpf_prog *fp);
 
 const struct bpf_func_proto *bpf_get_trace_printk_proto(void);
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index a3e571688421..607d5322ef94 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -17,6 +17,7 @@
  * Kris Katterjohn - Added many additional checks in bpf_check_classic()
  */
 
+#include <crypto/hash.h>
 #include <uapi/linux/btf.h>
 #include <linux/filter.h>
 #include <linux/skbuff.h>
@@ -287,6 +288,44 @@ void __bpf_prog_free(struct bpf_prog *fp)
 	vfree(fp);
 }
 
+int bpf_sha256(u8 *data, size_t data_size, u8 *output_digest)
+{
+	struct crypto_shash *tfm;
+	struct shash_desc *shash_desc;
+	size_t desc_size;
+	int ret = 0;
+
+	tfm = crypto_alloc_shash("sha256", 0, 0);
+	if (IS_ERR(tfm))
+		return PTR_ERR(tfm);
+
+
+	desc_size = crypto_shash_descsize(tfm) + sizeof(*shash_desc);
+	shash_desc = kmalloc(desc_size, GFP_KERNEL);
+	if (!shash_desc) {
+		crypto_free_shash(tfm);
+		return -ENOMEM;
+	}
+
+	shash_desc->tfm = tfm;
+	ret = crypto_shash_init(shash_desc);
+	if (ret)
+		goto out_free_desc;
+
+	ret = crypto_shash_update(shash_desc, data, data_size);
+	if (ret)
+		goto out_free_desc;
+
+	ret = crypto_shash_final(shash_desc, output_digest);
+	if (ret)
+		goto out_free_desc;
+
+out_free_desc:
+	kfree(shash_desc);
+	crypto_free_shash(tfm);
+	return ret;
+}
+
 int bpf_prog_calc_tag(struct bpf_prog *fp)
 {
 	const u32 bits_offset = SHA1_BLOCK_SIZE - sizeof(__be64);
-- 
2.43.0