[PATCH net-next 3/3] ipv6: sr: Prepare HMAC key ahead of time

[Eric Biggers <ebiggers@kernel.org>]

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.

As a side effect, invalid values for SEG6_ATTR_ALGID (i.e., values other
than SEG6_HMAC_ALGO_SHA1 and SEG6_HMAC_ALGO_SHA256) now cause an error
immediately when the key is added, rather than later when computing a
HMAC value is attempted.  This seems like the expected behavior anyway.

Signed-off-by: Eric Biggers <ebiggers@kernel.org>
---
 include/net/seg6_hmac.h |  8 ++++++++
 net/ipv6/seg6.c         | 13 +++++++++++++
 net/ipv6/seg6_hmac.c    |  9 ++++-----
 3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/include/net/seg6_hmac.h b/include/net/seg6_hmac.h
index 3fe4123dbbf0a..e9f41725933e4 100644
--- a/include/net/seg6_hmac.h
+++ b/include/net/seg6_hmac.h
@@ -7,10 +7,12 @@
  */
 
 #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>
 #include <linux/ip.h>
 #include <linux/ipv6.h>
@@ -24,13 +26,19 @@
 struct seg6_hmac_info {
 	struct rhash_head node;
 	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,
 			     struct ipv6_sr_hdr *hdr, struct in6_addr *saddr,
 			     u8 *output);
diff --git a/net/ipv6/seg6.c b/net/ipv6/seg6.c
index a5c4c629b788c..313acdf1b2158 100644
--- a/net/ipv6/seg6.c
+++ b/net/ipv6/seg6.c
@@ -211,10 +211,23 @@ static int seg6_genl_sethmac(struct sk_buff *skb, struct genl_info *info)
 	memcpy(hinfo->secret, secret, slen);
 	hinfo->slen = slen;
 	hinfo->alg_id = algid;
 	hinfo->hmackeyid = hmackeyid;
 
+	switch (algid) {
+	case SEG6_HMAC_ALGO_SHA1:
+		hmac_sha1_preparekey(&hinfo->key.sha1, secret, slen);
+		break;
+	case SEG6_HMAC_ALGO_SHA256:
+		hmac_sha256_preparekey(&hinfo->key.sha256, secret, slen);
+		break;
+	default:
+		kfree(hinfo);
+		err = -EINVAL;
+		goto out_unlock;
+	}
+
 	err = seg6_hmac_info_add(net, hmackeyid, hinfo);
 	if (err)
 		kfree(hinfo);
 
 out_unlock:
diff --git a/net/ipv6/seg6_hmac.c b/net/ipv6/seg6_hmac.c
index 816aef69e0cea..5cdcb3011cb3e 100644
--- a/net/ipv6/seg6_hmac.c
+++ b/net/ipv6/seg6_hmac.c
@@ -146,23 +146,22 @@ int seg6_hmac_compute(struct seg6_hmac_info *hinfo, struct ipv6_sr_hdr *hdr,
 		off += 16;
 	}
 
 	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);
 	local_bh_enable();
 	return ret;
-- 
2.50.1