libbpf: Don't use AF_ALG for SHA-256

Reimplement libbpf_sha256() using some basic SHA-256 C code.  This
eliminates the newly-added dependency on AF_ALG, which is a problematic
UAPI that is not supported by all kernels.

Make libbpf_sha256() return void, since it can no longer fail.  This
simplifies some callers.  Also drop the unnecessary 'sha_out_sz'
parameter.  Finally, also fix the typo in "compute_sha_udpate_offsets".

Tested by uncommenting the included test code and running
'make -C tools/bpf/bpftool', which causes the test to be executed.

Fixes: c297fe3 ("libbpf: Implement SHA256 internal helper")
Signed-off-by: Eric Biggers <[email protected]>

Author: Eric Biggers

tools/lib/bpf/gen_loader.c

@@ -371,7 +371,7 @@ static void emit_sys_close_blob(struct bpf_gen *gen, int blob_off)
 	__emit_sys_close(gen);
 }
 
-static int compute_sha_udpate_offsets(struct bpf_gen *gen);
+static void compute_sha_update_offsets(struct bpf_gen *gen);
 
 int bpf_gen__finish(struct bpf_gen *gen, int nr_progs, int nr_maps)
 {
@@ -399,11 +399,8 @@ int bpf_gen__finish(struct bpf_gen *gen, int nr_progs, int nr_maps)
 			      blob_fd_array_off(gen, i));
 	emit(gen, BPF_MOV64_IMM(BPF_REG_0, 0));
 	emit(gen, BPF_EXIT_INSN());
-	if (OPTS_GET(gen->opts, gen_hash, false)) {
-		gen->error = compute_sha_udpate_offsets(gen);
-		if (gen->error)
-			return gen->error;
-	}
+	if (OPTS_GET(gen->opts, gen_hash, false))
+		compute_sha_update_offsets(gen);
 
 	pr_debug("gen: finish %s\n", errstr(gen->error));
 	if (!gen->error) {
@@ -457,25 +454,20 @@ void bpf_gen__free(struct bpf_gen *gen)
 	_val;							\
 })
 
-static int compute_sha_udpate_offsets(struct bpf_gen *gen)
+static void compute_sha_update_offsets(struct bpf_gen *gen)
 {
 	__u64 sha[SHA256_DWORD_SIZE];
 	__u64 sha_dw;
-	int i, err;
+	int i;
 
-	err = libbpf_sha256(gen->data_start, gen->data_cur - gen->data_start, sha, SHA256_DIGEST_LENGTH);
-	if (err < 0) {
-		pr_warn("sha256 computation of the metadata failed");
-		return err;
-	}
+	libbpf_sha256(gen->data_start, gen->data_cur - gen->data_start, (__u8 *)sha);
 	for (i = 0; i < SHA256_DWORD_SIZE; i++) {
 		struct bpf_insn *insn =
 			(struct bpf_insn *)(gen->insn_start + gen->hash_insn_offset[i]);
 		sha_dw = tgt_endian(sha[i]);
 		insn[0].imm = (__u32)sha_dw;
 		insn[1].imm = sha_dw >> 32;
 	}
-	return 0;
 }
 
 void bpf_gen__load_btf(struct bpf_gen *gen, const void *btf_raw_data,

tools/lib/bpf/libbpf.c

@@ -35,6 +35,7 @@
 #include <linux/perf_event.h>
 #include <linux/bpf_perf_event.h>
 #include <linux/ring_buffer.h>
+#include <linux/unaligned.h>
 #include <sys/epoll.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>
@@ -43,9 +44,6 @@
 #include <sys/vfs.h>
 #include <sys/utsname.h>
 #include <sys/resource.h>
-#include <sys/socket.h>
-#include <linux/if_alg.h>
-#include <linux/socket.h>
 #include <libelf.h>
 #include <gelf.h>
 #include <zlib.h>
@@ -4491,7 +4489,7 @@ bpf_object__section_to_libbpf_map_type(const struct bpf_object *obj, int shndx)
 static int bpf_prog_compute_hash(struct bpf_program *prog)
 {
 	struct bpf_insn *purged;
-	int i, err;
+	int i, err = 0;
 
 	purged = calloc(prog->insns_cnt, BPF_INSN_SZ);
 	if (!purged)
@@ -4519,8 +4517,8 @@ static int bpf_prog_compute_hash(struct bpf_program *prog)
 			purged[i].imm = 0;
 		}
 	}
-	err = libbpf_sha256(purged, prog->insns_cnt * sizeof(struct bpf_insn),
-			    prog->hash, SHA256_DIGEST_LENGTH);
+	libbpf_sha256(purged, prog->insns_cnt * sizeof(struct bpf_insn),
+		      prog->hash);
 out:
 	free(purged);
 	return err;
@@ -14288,58 +14286,125 @@ void bpf_object__destroy_skeleton(struct bpf_object_skeleton *s)
 	free(s);
 }
 
-int libbpf_sha256(const void *data, size_t data_sz, void *sha_out, size_t sha_out_sz)
+static inline __u32 ror32(__u32 v, int bits)
 {
-	struct sockaddr_alg sa = {
-		.salg_family = AF_ALG,
-		.salg_type   = "hash",
-		.salg_name   = "sha256"
-	};
-	int sock_fd = -1;
-	int op_fd = -1;
-	int err = 0;
+	return (v >> bits) | (v << (32 - bits));
+}
 
-	if (sha_out_sz != SHA256_DIGEST_LENGTH) {
-		pr_warn("sha_out_sz should be exactly 32 bytes for a SHA256 digest");
-		return -EINVAL;
-	}
+#define SHA256_BLOCK_LENGTH 64
+#define Ch(x, y, z) (((x) & (y)) ^ (~(x) & (z)))
+#define Maj(x, y, z) (((x) & (y)) ^ ((x) & (z)) ^ ((y) & (z)))
+#define Sigma_0(x) (ror32((x), 2) ^ ror32((x), 13) ^ ror32((x), 22))
+#define Sigma_1(x) (ror32((x), 6) ^ ror32((x), 11) ^ ror32((x), 25))
+#define sigma_0(x) (ror32((x), 7) ^ ror32((x), 18) ^ ((x) >> 3))
+#define sigma_1(x) (ror32((x), 17) ^ ror32((x), 19) ^ ((x) >> 10))
 
-	sock_fd = socket(AF_ALG, SOCK_SEQPACKET, 0);
-	if (sock_fd < 0) {
-		err = -errno;
-		pr_warn("failed to create AF_ALG socket for SHA256: %s\n", errstr(err));
-		return err;
-	}
+static const __u32 sha256_K[64] = {
+	0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1,
+	0x923f82a4, 0xab1c5ed5, 0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3,
+	0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174, 0xe49b69c1, 0xefbe4786,
+	0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
+	0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147,
+	0x06ca6351, 0x14292967, 0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13,
+	0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85, 0xa2bfe8a1, 0xa81a664b,
+	0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
+	0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a,
+	0x5b9cca4f, 0x682e6ff3, 0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208,
+	0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2,
+};
 
-	if (bind(sock_fd, (struct sockaddr *)&sa, sizeof(sa)) < 0) {
-		err = -errno;
-		pr_warn("failed to bind to AF_ALG socket for SHA256: %s\n", errstr(err));
-		goto out;
-	}
+#define SHA256_ROUND(i, a, b, c, d, e, f, g, h)                                \
+	{                                                                      \
+		__u32 tmp = h + Sigma_1(e) + Ch(e, f, g) + sha256_K[i] + w[i]; \
+		d += tmp;                                                      \
+		h = tmp + Sigma_0(a) + Maj(a, b, c);                           \
+	}
+
+static void sha256_blocks(__u32 state[8], const __u8 *data, size_t nblocks)
+{
+	while (nblocks--) {
+		__u32 a = state[0];
+		__u32 b = state[1];
+		__u32 c = state[2];
+		__u32 d = state[3];
+		__u32 e = state[4];
+		__u32 f = state[5];
+		__u32 g = state[6];
+		__u32 h = state[7];
+		__u32 w[64];
+		int i;
+
+		for (i = 0; i < 16; i++)
+			w[i] = get_unaligned_be32(&data[4 * i]);
+		for (; i < ARRAY_SIZE(w); i++)
+			w[i] = sigma_1(w[i - 2]) + w[i - 7] +
+			       sigma_0(w[i - 15]) + w[i - 16];
+		for (i = 0; i < ARRAY_SIZE(w); i += 8) {
+			SHA256_ROUND(i + 0, a, b, c, d, e, f, g, h);
+			SHA256_ROUND(i + 1, h, a, b, c, d, e, f, g);
+			SHA256_ROUND(i + 2, g, h, a, b, c, d, e, f);
+			SHA256_ROUND(i + 3, f, g, h, a, b, c, d, e);
+			SHA256_ROUND(i + 4, e, f, g, h, a, b, c, d);
+			SHA256_ROUND(i + 5, d, e, f, g, h, a, b, c);
+			SHA256_ROUND(i + 6, c, d, e, f, g, h, a, b);
+			SHA256_ROUND(i + 7, b, c, d, e, f, g, h, a);
+		}
+		state[0] += a;
+		state[1] += b;
+		state[2] += c;
+		state[3] += d;
+		state[4] += e;
+		state[5] += f;
+		state[6] += g;
+		state[7] += h;
+		data += SHA256_BLOCK_LENGTH;
+	}
+}
+
+void libbpf_sha256(const void *data, size_t len, __u8 out[SHA256_DIGEST_LENGTH])
+{
+	__u32 state[8] = { 0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a,
+			   0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19 };
+	const __be64 bitcount = cpu_to_be64((__u64)len * 8);
+	__u8 final_data[2 * SHA256_BLOCK_LENGTH] = { 0 };
+	size_t final_len = len % SHA256_BLOCK_LENGTH;
+	int i;
 
-	op_fd = accept(sock_fd, NULL, 0);
-	if (op_fd < 0) {
-		err = -errno;
-		pr_warn("failed to accept from AF_ALG socket for SHA256: %s\n", errstr(err));
-		goto out;
-	}
+	sha256_blocks(state, data, len / SHA256_BLOCK_LENGTH);
 
-	if (write(op_fd, data, data_sz) != data_sz) {
-		err = -errno;
-		pr_warn("failed to write data to AF_ALG socket for SHA256: %s\n", errstr(err));
-		goto out;
-	}
+	memcpy(final_data, data + len - final_len, final_len);
+	final_data[final_len] = 0x80;
+	final_len = round_up(final_len + 9, SHA256_BLOCK_LENGTH);
+	memcpy(&final_data[final_len - 8], &bitcount, 8);
 
-	if (read(op_fd, sha_out, SHA256_DIGEST_LENGTH) != SHA256_DIGEST_LENGTH) {
-		err = -errno;
-		pr_warn("failed to read SHA256 from AF_ALG socket: %s\n", errstr(err));
-		goto out;
-	}
+	sha256_blocks(state, final_data, final_len / SHA256_BLOCK_LENGTH);
 
-out:
-	if (op_fd >= 0)
-		close(op_fd);
-	if (sock_fd >= 0)
-		close(sock_fd);
-	return err;
+	for (i = 0; i < ARRAY_SIZE(state); i++)
+		put_unaligned_be32(state[i], &out[4 * i]);
+}
+
+#if 0 /* To test libbpf_sha256(), uncomment this.  Requires -lcrypto. */
+#include <openssl/sha.h>
+
+/* Test libbpf_sha256() for all lengths from 0 to 4096 bytes inclusively. */
+static void __attribute__((constructor)) test_libbpf_sha256(void)
+{
+	__u8 data[4096];
+	__u8 hash1[SHA256_DIGEST_LENGTH];
+	__u8 hash2[SHA256_DIGEST_LENGTH];
+	size_t i;
+
+	for (i = 0; i < sizeof(data); i++)
+		data[i] = rand();
+
+	for (i = 0; i <= sizeof(data); i++) {
+		libbpf_sha256(data, i, hash1);
+		SHA256(data, i, hash2); /* Uses OpenSSL */
+		if (memcmp(hash1, hash2, sizeof(hash1)) != 0) {
+			pr_warn("libbpf_sha256() test failed\n");
+			abort();
+		}
+	}
+	pr_info("libbpf_sha256() test passed\n");
 }
+#endif

tools/lib/bpf/libbpf_internal.h

@@ -739,5 +739,5 @@ int probe_fd(int fd);
 #define SHA256_DIGEST_LENGTH 32
 #define SHA256_DWORD_SIZE SHA256_DIGEST_LENGTH / sizeof(__u64)
 
-int libbpf_sha256(const void *data, size_t data_sz, void *sha_out, size_t sha_out_sz);
+void libbpf_sha256(const void *data, size_t len, __u8 out[SHA256_DIGEST_LENGTH]);
 #endif /* __LIBBPF_LIBBPF_INTERNAL_H */