xen/vmac: Const the key parameter of vmac_set_key()

ECLAIR reports that tboot_gen_domain_integrity() is casting away
constness (Rule 11.8 violation).

vmac_set_key() doesn't modify the user_key parameter, so it can become const,
removing the need to cast.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/tboot.c

@@ -202,7 +202,7 @@ static void tboot_gen_domain_integrity(const uint8_t key[TB_KEY_SIZE],
     uint8_t nonce[16] = {};
     vmac_ctx_t ctx;
 
-    vmac_set_key((uint8_t *)key, &ctx);
+    vmac_set_key(key, &ctx);
     for_each_domain( d )
     {
         if ( !(d->options & XEN_DOMCTL_CDF_s3_integrity) )
@@ -241,7 +241,7 @@ static void tboot_gen_xenheap_integrity(const uint8_t key[TB_KEY_SIZE],
     uint8_t nonce[16] = {};
     vmac_ctx_t ctx;
 
-    vmac_set_key((uint8_t *)key, &ctx);
+    vmac_set_key(key, &ctx);
     for ( mfn = 0; mfn < max_page; mfn++ )
     {
         struct page_info *page = mfn_to_page(_mfn(mfn));
@@ -272,7 +272,7 @@ static void tboot_gen_frametable_integrity(const uint8_t key[TB_KEY_SIZE],
     uint8_t nonce[16] = {};
     vmac_ctx_t ctx;
 
-    vmac_set_key((uint8_t *)key, &ctx);
+    vmac_set_key(key, &ctx);
     for ( sidx = 0; ; sidx = nidx )
     {
         eidx = find_next_zero_bit(pdx_group_valid, max_idx, sidx);

xen/crypto/vmac.c

@@ -924,7 +924,7 @@ uint64_t vmac(unsigned char m[],
 
 /* ----------------------------------------------------------------------- */
 
-void vmac_set_key(unsigned char user_key[], vmac_ctx_t *ctx)
+void vmac_set_key(const unsigned char user_key[], vmac_ctx_t *ctx)
 {
     uint64_t in[2] = {0}, out[2];
     unsigned i;

xen/include/crypto/vmac.h

@@ -161,7 +161,7 @@ uint64_t vhash(unsigned char m[],
  * When passed a VMAC_KEY_LEN bit user_key, this function initialazies ctx.
  * ----------------------------------------------------------------------- */
 
-void vmac_set_key(unsigned char user_key[], vmac_ctx_t *ctx);
+void vmac_set_key(const unsigned char user_key[], vmac_ctx_t *ctx);
 
 /* --------------------------------------------------------------------- */