ipv6: sr: Prepare HMAC key ahead of time

Prepare the HMAC key when it is added to the kernel, instead of
preparing it implicitly for every packet. This significantly improves
the performance of seg6_hmac_compute(). A microbenchmark on x86_64
shows seg6_hmac_compute() (with HMAC-SHA256) dropping from ~1978 cycles
to ~1419 cycles, a 28% improvement.

The size of 'struct seg6_hmac_info' increases by 128 bytes, but that
should be fine, since there should not be a massive number of keys.

Signed-off-by: Eric Biggers <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

include/net/seg6_hmac.h

···
 #ifndef _NET_SEG6_HMAC_H
 #define _NET_SEG6_HMAC_H
 
+#include <crypto/sha1.h>
+#include <crypto/sha2.h>
 #include <net/flow.h>
 #include <net/ip6_fib.h>
 #include <net/sock.h>
···
 	struct rcu_head rcu;
 
 	u32 hmackeyid;
+	/* The raw key, kept only so it can be returned back to userspace */
 	char secret[SEG6_HMAC_SECRET_LEN];
 	u8 slen;
 	u8 alg_id;
+	/* The prepared key, which the calculations actually use */
+	union {
+		struct hmac_sha1_key sha1;
+		struct hmac_sha256_key sha256;
+	} key;
 };
 
 extern int seg6_hmac_compute(struct seg6_hmac_info *hinfo,

net/ipv6/seg6_hmac.c

···
 
 	switch (hinfo->alg_id) {
 	case SEG6_HMAC_ALGO_SHA1:
-		hmac_sha1_usingrawkey(hinfo->secret, hinfo->slen, ring, plen,
-				      output);
+		hmac_sha1(&hinfo->key.sha1, ring, plen, output);
 		static_assert(SEG6_HMAC_FIELD_LEN > SHA1_DIGEST_SIZE);
 		memset(&output[SHA1_DIGEST_SIZE], 0,
 		       SEG6_HMAC_FIELD_LEN - SHA1_DIGEST_SIZE);
 		break;
 	case SEG6_HMAC_ALGO_SHA256:
-		hmac_sha256_usingrawkey(hinfo->secret, hinfo->slen, ring, plen,
-					output);
+		hmac_sha256(&hinfo->key.sha256, ring, plen, output);
 		static_assert(SEG6_HMAC_FIELD_LEN == SHA256_DIGEST_SIZE);
 		break;
 	default:
-		ret = -ENOENT;
+		WARN_ON_ONCE(1);
+		ret = -EINVAL;
 		break;
 	}
 	local_unlock_nested_bh(&hmac_storage.bh_lock);
···
 
 	switch (hinfo->alg_id) {
 	case SEG6_HMAC_ALGO_SHA1:
+		hmac_sha1_preparekey(&hinfo->key.sha1,
+				     hinfo->secret, hinfo->slen);
+		break;
 	case SEG6_HMAC_ALGO_SHA256:
+		hmac_sha256_preparekey(&hinfo->key.sha256,
+				       hinfo->secret, hinfo->slen);
 		break;
 	default:
 		return -EINVAL;