[PATCH v5 01/12] bpf: Update the bpf_prog_calc_tag to use SHA256

[KP Singh]

Exclusive maps restrict map access to specific programs using a hash.
The current hash used for this is SHA1, which is prone to collisions.
This patch uses SHA256, which  is more resilient against
collisions. This new hash is stored in bpf_prog and used by the verifier
to determine if a program can access a given exclusive map.

The original 64-bit tags are kept, as they are used by users as a short,
possibly colliding program identifier for non-security purposes.

Signed-off-by: KP Singh <kpsingh at kernel.org>
---
 include/linux/bpf.h | 6 +++++-
 kernel/bpf/Kconfig  | 2 +-
 kernel/bpf/core.c   | 5 ++---
 3 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 41f776071ff5..d75902074bd1 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -31,6 +31,7 @@
 #include <linux/memcontrol.h>
 #include <linux/cfi.h>
 #include <asm/rqspinlock.h>
+#include <crypto/sha2.h>
 
 struct bpf_verifier_env;
 struct bpf_verifier_log;
@@ -1717,7 +1718,10 @@ struct bpf_prog {
 	enum bpf_attach_type	expected_attach_type; /* For some prog types */
 	u32			len;		/* Number of filter blocks */
 	u32			jited_len;	/* Size of jited insns in bytes */
-	u8			tag[BPF_TAG_SIZE];
+	union {
+		u8 digest[SHA256_DIGEST_SIZE];
+		u8 tag[BPF_TAG_SIZE];
+	};
 	struct bpf_prog_stats __percpu *stats;
 	int __percpu		*active;
 	unsigned int		(*bpf_func)(const void *ctx,
diff --git a/kernel/bpf/Kconfig b/kernel/bpf/Kconfig
index 17067dcb4386..eb3de35734f0 100644
--- a/kernel/bpf/Kconfig
+++ b/kernel/bpf/Kconfig
@@ -3,7 +3,7 @@
 # BPF interpreter that, for example, classic socket filters depend on.
 config BPF
 	bool
-	select CRYPTO_LIB_SHA1
+	select CRYPTO_LIB_SHA256
 
 # Used by archs to tell that they support BPF JIT compiler plus which
 # flavour. Only one of the two can be selected for a specific arch since
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 1cda2589d4b3..9b64674df16b 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -39,6 +39,7 @@
 #include <linux/bpf_mem_alloc.h>
 #include <linux/memcontrol.h>
 #include <linux/execmem.h>
+#include <crypto/sha2.h>
 
 #include <asm/barrier.h>
 #include <linux/unaligned.h>
@@ -296,7 +297,6 @@ void __bpf_prog_free(struct bpf_prog *fp)
 int bpf_prog_calc_tag(struct bpf_prog *fp)
 {
 	size_t size = bpf_prog_insn_size(fp);
-	u8 digest[SHA1_DIGEST_SIZE];
 	struct bpf_insn *dst;
 	bool was_ld_map;
 	u32 i;
@@ -327,8 +327,7 @@ int bpf_prog_calc_tag(struct bpf_prog *fp)
 			was_ld_map = false;
 		}
 	}
-	sha1((const u8 *)dst, size, digest);
-	memcpy(fp->tag, digest, sizeof(fp->tag));
+	sha256((u8 *)dst, size, fp->digest);
 	vfree(dst);
 	return 0;
 }
-- 
2.43.0