[PATCH, RFC 27/62] keys/mktme: Strengthen the entropy of CPU generated MKTME keys

[Kirill A. Shutemov]

From: Alison Schofield <alison.schofield@xxxxxxxxx>

If users request CPU generated keys, mix additional entropy bits
from the kernel into the key programming fields used by the
hardware. This additional entropy may compensate for weak user
supplied, or CPU generated, entropy.

Signed-off-by: Alison Schofield <alison.schofield@xxxxxxxxx>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 security/keys/mktme_keys.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/security/keys/mktme_keys.c b/security/keys/mktme_keys.c
index a7ca32865a1c..9fdf482ea3e6 100644
--- a/security/keys/mktme_keys.c
+++ b/security/keys/mktme_keys.c
@@ -7,6 +7,7 @@
 #include <linux/key-type.h>
 #include <linux/mm.h>
 #include <linux/parser.h>
+#include <linux/random.h>
 #include <linux/string.h>
 #include <asm/intel_pconfig.h>
 #include <keys/mktme-type.h>
@@ -102,7 +103,8 @@ struct mktme_payload {
 static int mktme_program_keyid(int keyid, struct mktme_payload *payload)
 {
 	struct mktme_key_program *kprog = NULL;
-	int ret;
+	u8 kern_entropy[MKTME_AES_XTS_SIZE];
+	int ret, i;
 
 	kprog = kmem_cache_zalloc(mktme_prog_cache, GFP_ATOMIC);
 	if (!kprog)
@@ -114,6 +116,14 @@ static int mktme_program_keyid(int keyid, struct mktme_payload *payload)
 	memcpy(kprog->key_field_1, payload->data_key, MKTME_AES_XTS_SIZE);
 	memcpy(kprog->key_field_2, payload->tweak_key, MKTME_AES_XTS_SIZE);
 
+	/* Strengthen the entropy fields for CPU generated keys */
+	if ((payload->keyid_ctrl & 0xff) == MKTME_KEYID_SET_KEY_RANDOM) {
+		get_random_bytes(&kern_entropy, sizeof(kern_entropy));
+		for (i = 0; i < (MKTME_AES_XTS_SIZE); i++) {
+			kprog->key_field_1[i] ^= kern_entropy[i];
+			kprog->key_field_2[i] ^= kern_entropy[i];
+		}
+	}
 	ret = MKTME_PROG_SUCCESS;	/* Future programming call */
 	kmem_cache_free(mktme_prog_cache, kprog);
 	return ret;
-- 
2.20.1