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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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7
elf/Makefile
View file

@ -36,7 +36,7 @@ dl-routines = $(addprefix dl-,load lookup object reloc deps \
exception sort-maps lookup-direct \
call-libc-early-init write \
thread_gscope_wait tls_init_tp \
debug-symbols)
debug-symbols minimal-malloc)
ifeq (yes,$(use-ldconfig))
dl-routines += dl-cache
endif
@ -75,6 +75,11 @@ CFLAGS-dl-runtime.c += -fexceptions -fasynchronous-unwind-tables
CFLAGS-dl-lookup.c += -fexceptions -fasynchronous-unwind-tables
CFLAGS-dl-iteratephdr.c += $(uses-callbacks)
# Called during static library initialization, so turn stack-protection
# off for non-shared builds.
CFLAGS-dl-minimal-malloc.o = $(no-stack-protector)
CFLAGS-dl-minimal-malloc.op = $(no-stack-protector)
# On targets without __builtin_memset, rtld.c uses a hand-coded loop
# in _dl_start. Make sure this isn't turned into a call to regular memset.
ifeq (yes,$(have-loop-to-function))

112
elf/dl-minimal-malloc.c Normal file
View file

@ -0,0 +1,112 @@
/* Minimal malloc implementation for dynamic linker and static
initialization.
Copyright (C) 1995-2021 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <assert.h>
#include <string.h>
#include <ldsodefs.h>
#include <malloc/malloc-internal.h>
static void *alloc_ptr, *alloc_end, *alloc_last_block;
/* Allocate an aligned memory block. */
void *
__minimal_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. */
void *
__minimal_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
__minimal_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 *
__minimal_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;
}

122
elf/dl-minimal.c
View file

@ -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. */

7
elf/dl-tunables.c
View file

@ -31,6 +31,7 @@
#include <fcntl.h>
#include <ldsodefs.h>
#include <array_length.h>
#include <dl-minimal-malloc.h>
#define TUNABLES_INTERNAL 1
#include "dl-tunables.h"
@ -48,13 +49,13 @@ tunables_strdup (const char *in)
size_t i = 0;
while (in[i++] != '\0');
char *out = __sbrk (i);
char *out = __minimal_malloc (i + 1);
/* For most of the tunables code, we ignore user errors. However,
this is a system error - and running out of memory at program
startup should be reported, so we do. */
if (out == (void *)-1)
_dl_fatal_printf ("sbrk() failure while processing tunables\n");
if (out == NULL)
_dl_fatal_printf ("failed to allocate memory to process tunables\n");
while (i-- > 0)
out[i] = in[i];

28
sysdeps/generic/dl-minimal-malloc.h Normal file
View file

@ -0,0 +1,28 @@
/* Minimal malloc implementation for dynamic linker and static
initialization.
Copyright (C) 2021 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#ifndef _DL_MINIMAL_MALLOC_H
#define _DL_MINIMAL_MALLOC_H
extern void *__minimal_malloc (size_t n) attribute_hidden;
extern void *__minimal_calloc (size_t nmemb, size_t size) attribute_hidden;
extern void __minimal_free (void *ptr) attribute_hidden;
extern void *__minimal_realloc (void *ptr, size_t n) attribute_hidden;
#endif