Rework memory allocation to support alignment

colmmacc · colmmacc · commit 3a418cc17467 · 2015-07-23T14:45:33.000-07:00
This change adds an "allocated" attribute to s2n_blob structures
which tracks how much memory we have allocated for the blob. This
allows us to implement our own realloc with a simple greedy
alloator; always allocate a page aligned unit o memory that is
a multiple of the system page size.

This change also makes it possible to disable mlock. Future
changes will do this for some problematic test cases that trigger
mlock exhaustion.

Another future change will adjust our connection allocation
to use one page per s2n_connection and then multiple pages for
the I/O stuffers.
diff --git a/error/s2n_errno.c b/error/s2n_errno.c
@@ -36,7 +36,8 @@ struct s2n_error_translation EN[] = {
     { S2N_ERR_DECRYPT, "error decrypting data" },
     { S2N_ERR_MEMSET,  "error calling memset" },
     { S2N_ERR_MEMCPY,  "error calling memcpy" },
-    { S2N_ERR_REALLOC, "error calling realloc" },
+    { S2N_ERR_MADVISE, "error calling madvise" },
+    { S2N_ERR_ALLOC,   "error allocating memory" },
     { S2N_ERR_MLOCK,   "error calling mlock" },
     { S2N_ERR_FSTAT,   "error calling fstat" },
     { S2N_ERR_OPEN,    "error calling open" },
diff --git a/error/s2n_errno.h b/error/s2n_errno.h
@@ -27,7 +27,8 @@ typedef enum {
     S2N_ERR_DECRYPT,
     S2N_ERR_MEMSET,
     S2N_ERR_MEMCPY,
-    S2N_ERR_REALLOC,
+    S2N_ERR_MADVISE,
+    S2N_ERR_ALLOC,
     S2N_ERR_MLOCK,
     S2N_ERR_FSTAT,
     S2N_ERR_OPEN,
diff --git a/utils/s2n_blob.h b/utils/s2n_blob.h
@@ -20,6 +20,7 @@
 struct s2n_blob {
     uint8_t *data;
     uint32_t size;
+    uint32_t allocated;
 };
 
 extern int s2n_blob_init(struct s2n_blob *b, uint8_t *data, uint32_t size);
diff --git a/utils/s2n_mem.c b/utils/s2n_mem.c
@@ -14,6 +14,7 @@
  */
 
 #include <stdint.h>
+#include <unistd.h>
 #include <stdlib.h>
 #include <sys/mman.h>
 
@@ -23,48 +24,78 @@
 #include "utils/s2n_mem.h"
 #include "utils/s2n_safety.h"
 
+static long page_size = 4096;
+static int  use_mlock = 1;
+
+int s2n_mem_init(void)
+{
+    GUARD(page_size = sysconf(_SC_PAGESIZE));
+    if (getenv("S2N_DONT_MLOCK")) {
+        use_mlock = 0;
+    }
+
+    return 0;
+}
+
 int s2n_alloc(struct s2n_blob *b, uint32_t size)
 {
     b->data = NULL;
-
+    b->size = 0;
+    b->allocated = 0;
     GUARD(s2n_realloc(b, size));
     return 0;
 }
 
 int s2n_realloc(struct s2n_blob *b, uint32_t size)
 {
     if (size == 0) {
-        GUARD(s2n_free(b));
+        return s2n_free(b);
+    }
+
+    if (size < b->allocated) {
+        b->size = size;
         return 0;
     }
 
-    uint8_t *data = realloc(b->data, size);
-    if (data == NULL) {
-        S2N_ERROR(S2N_ERR_REALLOC);
+    uint32_t allocate = page_size * ((size + (page_size - 1)) / page_size); 
+
+    void *data;
+    if (posix_memalign(&data, page_size, allocate)) {
+        S2N_ERROR(S2N_ERR_ALLOC);
     }
-    b->data = data;
-    if (mlock(b->data, size) < 0) {
-        GUARD(s2n_free(b));
-        S2N_ERROR(S2N_ERR_MLOCK);
+
+    if (b->size) {
+        memcpy_check(data, b->data, b->size);
     }
+
+    b->data = data;
+    b->size = size;
+    b->allocated = allocate;
+
 #ifdef MADV_DONTDUMP
     if (madvise(b->data, size, MADV_DONTDUMP) < 0) {
         GUARD(s2n_free(b));
         S2N_ERROR(S2N_ERR_MADVISE);
     }
 #endif
-    b->size = size;
+    if (use_mlock == 0) {
+        return 0;
+    }
+
+    if (mlock(b->data, size) < 0) {
+        GUARD(s2n_free(b));
+        S2N_ERROR(S2N_ERR_MLOCK);
+    }
 
     return 0;
 }
 
 int s2n_free(struct s2n_blob *b)
 {
-    if (b->data) {
-        free(b->data);
-    }
+    free(b->data);
     b->data = NULL;
     b->size = 0;
+    b->allocated = 0;
 
     return 0;
 }
diff --git a/utils/s2n_mem.h b/utils/s2n_mem.h
@@ -19,6 +19,7 @@
 
 #include <stdint.h>
 
+int s2n_mem_init(void);
 int s2n_alloc(struct s2n_blob *b, uint32_t size);
 int s2n_realloc(struct s2n_blob *b, uint32_t size);
 int s2n_free(struct s2n_blob *b);
diff --git a/utils/s2n_random.c b/utils/s2n_random.c
@@ -33,6 +33,7 @@
 
 #include "utils/s2n_safety.h"
 #include "utils/s2n_random.h"
+#include "utils/s2n_mem.h"
 
 #define ENTROPY_SOURCE "/dev/urandom"
 
@@ -186,6 +187,8 @@ RAND_METHOD s2n_openssl_rand_method = {
 
 int s2n_init(void)
 {
+    GUARD(s2n_mem_init());
+
     OPEN:
     entropy_fd = open(ENTROPY_SOURCE, O_RDONLY);
     if (entropy_fd == -1) {
