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Align the reference counted allocations

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We need stronger alignment guarantees for the memory allocations done
through g_rc_box_alloc_full(): while the passed block size may be
aligned, we're not aligning the private data size; this means the
overall allocation may become unaligned, and this could raise issues
when we use the private data size as an offset to access the reference
count.

Fixes: #1581
This commit is contained in:
Emmanuele Bassi 2018-11-14 14:43:23 +00:00
parent 2a64176b83
commit 87f0a5a219
3 changed files with 73 additions and 15 deletions
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10
glib/garcbox.c
View File

@ -177,7 +177,7 @@ g_atomic_rc_box_alloc (gsize block_size)
{
g_return_val_if_fail (block_size > 0, NULL);
return g_rc_box_alloc_full (block_size, TRUE, FALSE);
return g_rc_box_alloc_full (block_size, STRUCT_ALIGNMENT, TRUE, FALSE);
}
/**
@ -201,7 +201,7 @@ g_atomic_rc_box_alloc0 (gsize block_size)
{
g_return_val_if_fail (block_size > 0, NULL);
return g_rc_box_alloc_full (block_size, TRUE, TRUE);
return g_rc_box_alloc_full (block_size, STRUCT_ALIGNMENT, TRUE, TRUE);
}
/**
@ -262,7 +262,7 @@ gpointer
g_return_val_if_fail (block_size > 0, NULL);
g_return_val_if_fail (mem_block != NULL, NULL);
res = g_rc_box_alloc_full (block_size, TRUE, FALSE);
res = g_rc_box_alloc_full (block_size, STRUCT_ALIGNMENT, TRUE, FALSE);
memcpy (res, mem_block, block_size);
return res;
@ -339,13 +339,15 @@ g_atomic_rc_box_release_full (gpointer mem_block,
if (g_atomic_ref_count_dec (&real_box->ref_count))
{
char *real_mem = (char *) real_box - real_box->private_offset;
TRACE (GLIB_RCBOX_RELEASE (mem_block, 1));
if (clear_func != NULL)
clear_func (mem_block);
TRACE (GLIB_RCBOX_FREE (mem_block));
g_free (real_box);
g_free (real_mem);
}
}

68
glib/grcbox.c
View File

@ -162,25 +162,49 @@
* Since: 2.58.
*/
#define G_RC_BOX(p) (GRcBox *) (((char *) (p)) - G_RC_BOX_SIZE)
/* We use the same alignment as GTypeInstance and GNU libc's malloc */
#define STRUCT_ALIGNMENT (2 * sizeof (gsize))
#define ALIGN_STRUCT(offset) ((offset + (STRUCT_ALIGNMENT - 1)) & -STRUCT_ALIGNMENT)
#define G_RC_BOX(p) (GRcBox *) (((char *) (p)) - G_RC_BOX_SIZE)
gpointer
g_rc_box_alloc_full (gsize block_size,
gsize alignment,
gboolean atomic,
gboolean clear)
{
/* sizeof GArcBox == sizeof GRcBox */
/* We don't do an (atomic ? G_ARC_BOX_SIZE : G_RC_BOX_SIZE) check, here
* because we have a static assertion that sizeof(GArcBox) == sizeof(GRcBox)
* inside grcboxprivate.h, and we don't want the compiler to unnecessarily
* warn about both branches of the conditional yielding identical results
*/
gsize private_size = G_ARC_BOX_SIZE;
gsize private_offset = 0;
gsize real_size;
char *allocated;
g_assert (block_size < (G_MAXSIZE - G_ARC_BOX_SIZE));
g_assert (alignment != 0);
/* We need to ensure that the private data is aligned */
if (private_size % alignment != 0)
{
private_offset = private_size % alignment;
private_size += (alignment - private_offset);
}
g_assert (block_size < (G_MAXSIZE - private_size));
real_size = private_size + block_size;
/* The real allocated size must be a multiple of @alignment, to
* maintain the alignment of block_size
*/
if (real_size % alignment != 0)
{
gsize offset = real_size % alignment;
g_assert (real_size < (G_MAXSIZE - (alignment - offset)));
real_size += (alignment - offset);
}
#ifdef ENABLE_VALGRIND
if (RUNNING_ON_VALGRIND)
{
@ -214,8 +238,18 @@ g_rc_box_alloc_full (gsize block_size,
if (atomic)
{
GArcBox *real_box = (GArcBox *) allocated;
/* We leave the alignment padding at the top of the allocation,
* so we have an in memory layout of:
*
* |[ offset ][ sizeof(GArcBox) ]||[ block_size ]|
*/
GArcBox *real_box = (GArcBox *) (allocated + private_offset);
/* Store the real size */
real_box->mem_size = block_size;
/* Store the alignment offset, to be used when freeing the
* allocated block
*/
real_box->private_offset = private_offset;
#ifndef G_DISABLE_ASSERT
real_box->magic = G_BOX_MAGIC;
#endif
@ -223,8 +257,18 @@ g_rc_box_alloc_full (gsize block_size,
}
else
{
GRcBox *real_box = (GRcBox *) allocated;
/* We leave the alignment padding at the top of the allocation,
* so we have an in memory layout of:
*
* |[ offset ][ sizeof(GRcBox) ]||[ block_size ]|
*/
GRcBox *real_box = (GRcBox *) (allocated + private_offset);
/* Store the real size */
real_box->mem_size = block_size;
/* Store the alignment offset, to be used when freeing the
* allocated block
*/
real_box->private_offset = private_offset;
#ifndef G_DISABLE_ASSERT
real_box->magic = G_BOX_MAGIC;
#endif
@ -255,7 +299,7 @@ g_rc_box_alloc (gsize block_size)
{
g_return_val_if_fail (block_size > 0, NULL);
return g_rc_box_alloc_full (block_size, FALSE, FALSE);
return g_rc_box_alloc_full (block_size, STRUCT_ALIGNMENT, FALSE, FALSE);
}
/**
@ -279,7 +323,7 @@ g_rc_box_alloc0 (gsize block_size)
{
g_return_val_if_fail (block_size > 0, NULL);
return g_rc_box_alloc_full (block_size, FALSE, TRUE);
return g_rc_box_alloc_full (block_size, STRUCT_ALIGNMENT, FALSE, TRUE);
}
/**
@ -339,7 +383,7 @@ gpointer
g_return_val_if_fail (block_size > 0, NULL);
g_return_val_if_fail (mem_block != NULL, NULL);
res = g_rc_box_alloc_full (block_size, FALSE, FALSE);
res = g_rc_box_alloc_full (block_size, STRUCT_ALIGNMENT, FALSE, FALSE);
memcpy (res, mem_block, block_size);
return res;
@ -416,13 +460,15 @@ g_rc_box_release_full (gpointer mem_block,
if (g_ref_count_dec (&real_box->ref_count))
{
char *real_mem = (char *) real_box - real_box->private_offset;
TRACE (GLIB_RCBOX_RELEASE (mem_block, 0));
if (clear_func != NULL)
clear_func (mem_block);
TRACE (GLIB_RCBOX_FREE (mem_block));
g_free (real_box);
g_free (real_mem);
}
}

10
glib/grcboxprivate.h
View File

@ -27,6 +27,7 @@ typedef struct {
grefcount ref_count;
gsize mem_size;
gsize private_offset;
#ifndef G_DISABLE_ASSERT
/* A "magic" number, used to perform additional integrity
@ -40,6 +41,7 @@ typedef struct {
gatomicrefcount ref_count;
gsize mem_size;
gsize private_offset;
#ifndef G_DISABLE_ASSERT
guint32 magic;
@ -51,10 +53,18 @@ typedef struct {
/* Keep the two refcounted boxes identical in size */
G_STATIC_ASSERT (sizeof (GRcBox) == sizeof (GArcBox));
/* This is the default alignment we use when allocating the
* refcounted memory blocks; it's similar to the alignment
* guaranteed by the malloc() in GNU's libc and by the GSlice
* allocator
*/
#define STRUCT_ALIGNMENT (2 * sizeof (gsize))
#define G_RC_BOX_SIZE sizeof (GRcBox)
#define G_ARC_BOX_SIZE sizeof (GArcBox)
gpointer g_rc_box_alloc_full (gsize block_size,
gsize alignment,
gboolean atomic,
gboolean clear);