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Slab: head now uses bitmask for used/free nodes info instead of lists

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From now, there are no auxiliary pointers stored in the free slab nodes.
This led to strange debugging problems if use-after-free happened in
slab-allocated structures, especially if the structure's first member is
a next pointer.

This also reduces the memory needed by 1 pointer per allocated object.
OTOH, we now rely on pages being aligned to their size's multiple, which
is quite common anyway.
This commit is contained in:
Maria Matejka
2020-07-22 00:09:15 +02:00
parent 82f19ba95e
commit 886dd92eee
6 changed files with 150 additions and 70 deletions
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2
sysdep/unix/Makefile
View File

@@ -1,4 +1,4 @@
src := io.c krt.c log.c main.c random.c
src := alloc.c io.c krt.c log.c main.c random.c
obj := $(src-o-files)
$(all-daemon)
$(cf-local)

80
sysdep/unix/alloc.c Normal file
View File

@@ -0,0 +1,80 @@
/*
* BIRD Internet Routing Daemon -- Raw allocation
*
* (c) 2020 Maria Matejka <mq@ucw.cz>
*
* Can be freely distributed and used under the terms of the GNU GPL.
*/
#include "nest/bird.h"
#include "lib/resource.h"
#include <stdlib.h>
#include <unistd.h>
#ifdef HAVE_MMAP
#include <sys/mman.h>
#endif
#ifdef HAVE_MMAP
static u64 page_size = 0;
static _Bool use_fake = 0;
#else
static const u64 page_size = 4096; /* Fake page size */
#endif
u64 get_page_size(void)
{
if (page_size)
return page_size;
#ifdef HAVE_MMAP
if (page_size = sysconf(_SC_PAGESIZE))
{
if ((u64_popcount(page_size) > 1) || (page_size > 16384))
{
/* Too big or strange page, use the aligned allocator instead */
page_size = 4096;
use_fake = 1;
}
return page_size;
}
bug("Page size must be non-zero");
#endif
}
void *
alloc_page(void)
{
#ifdef HAVE_MMAP
if (!use_fake)
{
void *ret = mmap(NULL, get_page_size(), PROT_WRITE | PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (ret == MAP_FAILED)
bug("mmap(%lu) failed: %m", page_size);
return ret;
}
else
#endif
{
void *ret = aligned_alloc(page_size, page_size);
if (!ret)
bug("aligned_alloc(%lu) failed", page_size);
return ret;
}
}
void
free_page(void *ptr)
{
#ifdef HAVE_MMAP
if (!use_fake)
{
if (munmap(ptr, get_page_size()) < 0)
bug("munmap(%p) failed: %m", ptr);
}
else
#endif
free(ptr);
}