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elf: Use the minimal malloc on tunables_strdup

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The rtld_malloc functions are moved to its own file so it can be
used on csu code.  Also, the functiosn are renamed to __minimal_*
(since there are now used not only on loader code).

Using the __minimal_malloc on tunables_strdup() avoids potential
issues with sbrk() calls while processing the tunables (I see
sporadic elf/tst-dso-ordering9 on powerpc64le with different
tests failing due ASLR).

Also, using __minimal_malloc over plain mmap optimizes the memory
allocation on both static and dynamic case (since it will any unused
space in either the last page of data segments, avoiding mmap() call,
or from the previous mmap() call).

Checked on x86_64-linux-gnu, i686-linux-gnu, and powerpc64le-linux-gnu.

Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
This commit is contained in:
Adhemerval Zanella
2021-11-03 11:20:50 -03:00
parent db6c4935fa
commit b05fae4d8e
5 changed files with 157 additions and 119 deletions
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122
elf/dl-minimal.c
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@@ -16,23 +16,14 @@
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <errno.h>
#include <limits.h>
#include <stdio.h>
#include <string.h>
#include <tls.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/param.h>
#include <sys/types.h>
#include <assert.h>
#include <ldsodefs.h>
#include <dl-irel.h>
#include <dl-hash.h>
#include <dl-sym-post.h>
#include <_itoa.h>
#include <malloc/malloc-internal.h>
#include <dl-minimal-malloc.h>
#include <assert.h>
/* The rtld startup code calls __rtld_malloc_init_stubs after the
first self-relocation to adjust the pointers to the minimal
@@ -44,19 +35,13 @@ __typeof (free) *__rtld_free attribute_relro;
__typeof (malloc) *__rtld_malloc attribute_relro;
__typeof (realloc) *__rtld_realloc attribute_relro;
/* Defined below. */
static __typeof (calloc) rtld_calloc;
static __typeof (free) rtld_free;
static __typeof (malloc) rtld_malloc;
static __typeof (realloc) rtld_realloc;
void
__rtld_malloc_init_stubs (void)
{
__rtld_calloc = &rtld_calloc;
__rtld_free = &rtld_free;
__rtld_malloc = &rtld_malloc;
__rtld_realloc = &rtld_realloc;
__rtld_calloc = &__minimal_calloc;
__rtld_free = &__minimal_free;
__rtld_malloc = &__minimal_malloc;
__rtld_realloc = &__minimal_realloc;
}
bool
@@ -64,7 +49,7 @@ __rtld_malloc_is_complete (void)
{
/* The caller assumes that there is an active malloc. */
assert (__rtld_malloc != NULL);
return __rtld_malloc != &rtld_malloc;
return __rtld_malloc != &__minimal_malloc;
}
/* Lookup NAME at VERSION in the scope of MATCH. */
@@ -115,99 +100,6 @@ __rtld_malloc_init_real (struct link_map *main_map)
__rtld_realloc = new_realloc;
}
/* Minimal malloc allocator for used during initial link. After the
initial link, a full malloc implementation is interposed, either
the one in libc, or a different one supplied by the user through
interposition. */
static void *alloc_ptr, *alloc_end, *alloc_last_block;
/* Allocate an aligned memory block. */
static void *
rtld_malloc (size_t n)
{
if (alloc_end == 0)
{
/* Consume any unused space in the last page of our data segment. */
extern int _end attribute_hidden;
alloc_ptr = &_end;
alloc_end = (void *) 0 + (((alloc_ptr - (void *) 0)
+ GLRO(dl_pagesize) - 1)
& ~(GLRO(dl_pagesize) - 1));
}
/* Make sure the allocation pointer is ideally aligned. */
alloc_ptr = (void *) 0 + (((alloc_ptr - (void *) 0) + MALLOC_ALIGNMENT - 1)
& ~(MALLOC_ALIGNMENT - 1));
if (alloc_ptr + n >= alloc_end || n >= -(uintptr_t) alloc_ptr)
{
/* Insufficient space left; allocate another page plus one extra
page to reduce number of mmap calls. */
caddr_t page;
size_t nup = (n + GLRO(dl_pagesize) - 1) & ~(GLRO(dl_pagesize) - 1);
if (__glibc_unlikely (nup == 0 && n != 0))
return NULL;
nup += GLRO(dl_pagesize);
page = __mmap (0, nup, PROT_READ|PROT_WRITE,
MAP_ANON|MAP_PRIVATE, -1, 0);
if (page == MAP_FAILED)
return NULL;
if (page != alloc_end)
alloc_ptr = page;
alloc_end = page + nup;
}
alloc_last_block = (void *) alloc_ptr;
alloc_ptr += n;
return alloc_last_block;
}
/* We use this function occasionally since the real implementation may
be optimized when it can assume the memory it returns already is
set to NUL. */
static void *
rtld_calloc (size_t nmemb, size_t size)
{
/* New memory from the trivial malloc above is always already cleared.
(We make sure that's true in the rare occasion it might not be,
by clearing memory in free, below.) */
size_t bytes = nmemb * size;
#define HALF_SIZE_T (((size_t) 1) << (8 * sizeof (size_t) / 2))
if (__builtin_expect ((nmemb | size) >= HALF_SIZE_T, 0)
&& size != 0 && bytes / size != nmemb)
return NULL;
return malloc (bytes);
}
/* This will rarely be called. */
void
rtld_free (void *ptr)
{
/* We can free only the last block allocated. */
if (ptr == alloc_last_block)
{
/* Since this is rare, we clear the freed block here
so that calloc can presume malloc returns cleared memory. */
memset (alloc_last_block, '\0', alloc_ptr - alloc_last_block);
alloc_ptr = alloc_last_block;
}
}
/* This is only called with the most recent block returned by malloc. */
void *
rtld_realloc (void *ptr, size_t n)
{
if (ptr == NULL)
return malloc (n);
assert (ptr == alloc_last_block);
size_t old_size = alloc_ptr - alloc_last_block;
alloc_ptr = alloc_last_block;
void *new = malloc (n);
return new != ptr ? memcpy (new, ptr, old_size) : new;
}
/* Avoid signal frobnication in setjmp/longjmp. Keeps things smaller. */