Poly1305: Use |size_t|; assert |poly1305_state| is large enough.

Clarify that there are no truncation issues on targets where the range
of |unsigned| is smaller than the range of |size_t|.

Ensure that |poly1305_state| is (still) large enough. This is a good
idea independently of this change, but is especially important because
switching the fields to |size_t| might have enlarged the structures.

Change-Id: I16e408229c28fcba6c3592603ddb9431cf1f142d
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/44244
Commit-Queue: Adam Langley <agl@google.com>
Reviewed-by: Adam Langley <agl@google.com>

crypto/poly1305/poly1305.c

@@ -46,10 +46,14 @@ struct poly1305_state_st {
   uint32_t s1, s2, s3, s4;
   uint32_t h0, h1, h2, h3, h4;
   uint8_t buf[16];
-  unsigned int buf_used;
+  size_t buf_used;
   uint8_t key[16];
 };
 
+OPENSSL_STATIC_ASSERT(
+    sizeof(struct poly1305_state_st) + 63 <= sizeof(poly1305_state),
+    "poly1305_state isn't large enough to hold aligned poly1305_state_st");
+
 static inline struct poly1305_state_st *poly1305_aligned_state(
     poly1305_state *state) {
   return (struct poly1305_state_st *)(((uintptr_t)state + 63) & ~63);
@@ -200,7 +204,6 @@ void CRYPTO_poly1305_init(poly1305_state *statep, const uint8_t key[32]) {
 
 void CRYPTO_poly1305_update(poly1305_state *statep, const uint8_t *in,
                             size_t in_len) {
-  unsigned int i;
   struct poly1305_state_st *state = poly1305_aligned_state(statep);
 
 #if defined(OPENSSL_POLY1305_NEON)
@@ -211,11 +214,11 @@ void CRYPTO_poly1305_update(poly1305_state *statep, const uint8_t *in,
 #endif
 
   if (state->buf_used) {
-    unsigned todo = 16 - state->buf_used;
+    size_t todo = 16 - state->buf_used;
     if (todo > in_len) {
-      todo = (unsigned)in_len;
+      todo = in_len;
     }
-    for (i = 0; i < todo; i++) {
+    for (size_t i = 0; i < todo; i++) {
       state->buf[state->buf_used + i] = in[i];
     }
     state->buf_used += todo;
@@ -236,10 +239,10 @@ void CRYPTO_poly1305_update(poly1305_state *statep, const uint8_t *in,
   }
 
   if (in_len) {
-    for (i = 0; i < in_len; i++) {
+    for (size_t i = 0; i < in_len; i++) {
       state->buf[i] = in[i];
     }
-    state->buf_used = (unsigned)in_len;
+    state->buf_used = in_len;
   }
 }
 

crypto/poly1305/poly1305_arm.c

@@ -36,7 +36,7 @@ extern void addmulmod(fe1305x2 *r, const fe1305x2 *x, const fe1305x2 *y,
                       const fe1305x2 *c);
 
 extern int blocks(fe1305x2 *h, const fe1305x2 *precomp, const uint8_t *in,
-                  unsigned int inlen);
+                  size_t inlen);
 
 static void freeze(fe1305x2 *r) {
   int i;
@@ -136,7 +136,7 @@ static void fe1305x2_tobytearray(uint8_t r[16], fe1305x2 *x) {
 }
 
 static void fe1305x2_frombytearray(fe1305x2 *r, const uint8_t *x, size_t xlen) {
-  unsigned i;
+  size_t i;
   uint8_t t[17];
 
   for (i = 0; (i < 16) && (i < xlen); i++) {
@@ -179,17 +179,20 @@ static const alignas(16) fe1305x2 zero;
 struct poly1305_state_st {
   uint8_t data[sizeof(fe1305x2[5]) + 128];
   uint8_t buf[32];
-  unsigned int buf_used;
+  size_t buf_used;
   uint8_t key[16];
 };
 
+OPENSSL_STATIC_ASSERT(
+    sizeof(struct poly1305_state_st) + 63 <= sizeof(poly1305_state),
+    "poly1305_state isn't large enough to hold aligned poly1305_state_st.");
+
 void CRYPTO_poly1305_init_neon(poly1305_state *state, const uint8_t key[32]) {
   struct poly1305_state_st *st = (struct poly1305_state_st *)(state);
   fe1305x2 *const r = (fe1305x2 *)(st->data + (15 & (-(int)st->data)));
   fe1305x2 *const h = r + 1;
   fe1305x2 *const c = h + 1;
   fe1305x2 *const precomp = c + 1;
-  unsigned int j;
 
   r->v[1] = r->v[0] = 0x3ffffff & load32(key);
   r->v[3] = r->v[2] = 0x3ffff03 & (load32(key + 3) >> 2);
@@ -197,7 +200,7 @@ void CRYPTO_poly1305_init_neon(poly1305_state *state, const uint8_t key[32]) {
   r->v[7] = r->v[6] = 0x3f03fff & (load32(key + 9) >> 6);
   r->v[9] = r->v[8] = 0x00fffff & (load32(key + 12) >> 8);
 
-  for (j = 0; j < 10; j++) {
+  for (size_t j = 0; j < 10; j++) {
     h->v[j] = 0;  // XXX: should fast-forward a bit
   }
 
@@ -215,14 +218,13 @@ void CRYPTO_poly1305_update_neon(poly1305_state *state, const uint8_t *in,
   fe1305x2 *const h = r + 1;
   fe1305x2 *const c = h + 1;
   fe1305x2 *const precomp = c + 1;
-  unsigned int i;
 
   if (st->buf_used) {
-    unsigned int todo = 32 - st->buf_used;
+    size_t todo = 32 - st->buf_used;
     if (todo > in_len) {
       todo = in_len;
     }
-    for (i = 0; i < todo; i++) {
+    for (size_t i = 0; i < todo; i++) {
       st->buf[st->buf_used + i] = in[i];
     }
     st->buf_used += todo;
@@ -232,7 +234,7 @@ void CRYPTO_poly1305_update_neon(poly1305_state *state, const uint8_t *in,
     if (st->buf_used == sizeof(st->buf) && in_len) {
       addmulmod(h, h, precomp, &zero);
       fe1305x2_frombytearray(c, st->buf, sizeof(st->buf));
-      for (i = 0; i < 10; i++) {
+      for (size_t i = 0; i < 10; i++) {
         h->v[i] += c->v[i];
       }
       st->buf_used = 0;
@@ -240,7 +242,7 @@ void CRYPTO_poly1305_update_neon(poly1305_state *state, const uint8_t *in,
   }
 
   while (in_len > 32) {
-    unsigned int tlen = 1048576;
+    size_t tlen = 1048576;
     if (in_len < tlen) {
       tlen = in_len;
     }
@@ -250,7 +252,7 @@ void CRYPTO_poly1305_update_neon(poly1305_state *state, const uint8_t *in,
   }
 
   if (in_len) {
-    for (i = 0; i < in_len; i++) {
+    for (size_t i = 0; i < in_len; i++) {
       st->buf[i] = in[i];
     }
     st->buf_used = in_len;

crypto/poly1305/poly1305_vec.c

@@ -92,6 +92,10 @@ typedef struct poly1305_state_internal_t {
 } poly1305_state_internal; /* 448 bytes total + 63 bytes for
                               alignment = 511 bytes raw */
 
+OPENSSL_STATIC_ASSERT(
+    sizeof(struct poly1305_state_internal_t) + 63 <= sizeof(poly1305_state),
+    "poly1305_state isn't large enough to hold aligned poly1305_state_internal_t");
+
 static inline poly1305_state_internal *poly1305_aligned_state(
     poly1305_state *state) {
   return (poly1305_state_internal *)(((uint64_t)state + 63) & ~63);