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Add zfree to zero allocation before free

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Key and cookie management typically wants to
avoid information leaks by explicitly zeroing
before free. This routine simplifies that by
permitting consumers to do so without carrying
the size around.

Reviewed by:	jeff@, jhb@
MFC after:	1 week
Sponsored by:	Rubicon Communications, LLC (Netgate)
Differential Revision:	https://reviews.freebsd.org/D22790
This commit is contained in:
Matt Macy 2020-02-16 00:12:53 +00:00
parent bbb7a2c7c3
commit 45035becfe
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=357987
3 changed files with 58 additions and 0 deletions
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15
share/man/man9/malloc.9
View File

@ -49,6 +49,8 @@
.Fn mallocarray "size_t nmemb" "size_t size" "struct malloc_type *type" "int flags"
.Ft void
.Fn free "void *addr" "struct malloc_type *type"
.Ft void
.Fn zfree "void *addr" "struct malloc_type *type"
.Ft void *
.Fn realloc "void *addr" "size_t size" "struct malloc_type *type" "int flags"
.Ft void *
@ -106,6 +108,19 @@ then
.Fn free
does nothing.
.Pp
Like
.Fn free ,
the
.Fn zfree
function releases memory at address
.Fa addr
that was previously allocated by
.Fn malloc
for re-use.
However,
.Fn zfree
will zero the memory before it is released.
.Pp
The
.Fn realloc
function changes the size of the previously allocated memory referenced by

42
sys/kern/kern_malloc.c
View File

@ -820,6 +820,48 @@ free(void *addr, struct malloc_type *mtp)
malloc_type_freed(mtp, size);
}
/*
* zfree:
*
* Zero then free a block of memory allocated by malloc.
*
* This routine may not block.
*/
void
zfree(void *addr, struct malloc_type *mtp)
{
uma_zone_t zone;
uma_slab_t slab;
u_long size;
#ifdef MALLOC_DEBUG
if (free_dbg(&addr, mtp) != 0)
return;
#endif
/* free(NULL, ...) does nothing */
if (addr == NULL)
return;
vtozoneslab((vm_offset_t)addr & (~UMA_SLAB_MASK), &zone, &slab);
if (slab == NULL)
panic("free: address %p(%p) has not been allocated.\n",
addr, (void *)((u_long)addr & (~UMA_SLAB_MASK)));
if (__predict_true(!malloc_large_slab(slab))) {
size = zone->uz_size;
#ifdef INVARIANTS
free_save_type(addr, mtp, size);
#endif
explicit_bzero(addr, size);
uma_zfree_arg(zone, addr, slab);
} else {
size = malloc_large_size(slab);
explicit_bzero(addr, size);
free_large(addr, size);
}
malloc_type_freed(mtp, size);
}
void
free_domain(void *addr, struct malloc_type *mtp)
{

1
sys/sys/malloc.h
View File

@ -179,6 +179,7 @@ void *contigmalloc_domainset(unsigned long size, struct malloc_type *type,
unsigned long alignment, vm_paddr_t boundary)
__malloc_like __result_use_check __alloc_size(1) __alloc_align(7);
void free(void *addr, struct malloc_type *type);
void zfree(void *addr, struct malloc_type *type);
void free_domain(void *addr, struct malloc_type *type);
void *malloc(size_t size, struct malloc_type *type, int flags) __malloc_like
__result_use_check __alloc_size(1);