diff options
author | Florian Weimer <fweimer@redhat.com> | 2016-08-03 16:15:38 +0200 |
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committer | Florian Weimer <fweimer@redhat.com> | 2016-08-03 16:15:38 +0200 |
commit | a2ff21f825adb8821eeb6145197fa8b9a8a60a58 (patch) | |
tree | 65f74b90eb0a005a278f80586b0ee001d358021b /elf/dl-tls.c | |
parent | 5bc17330eb7667b96fee8baf3729c3310fa28b40 (diff) | |
download | glibc-a2ff21f825adb8821eeb6145197fa8b9a8a60a58.tar.gz |
elf: Avoid using memalign for TLS allocations [BZ #17730]
Instead of a flag which indicates the pointer can be freed, dtv_t
now includes the pointer which should be freed. Due to padding,
the size of dtv_t does not increase.
To avoid using memalign, the new allocate_dtv_entry function
allocates a sufficiently large buffer so that a sub-buffer
can be found in it which starts with an aligned pointer. Both
the aligned and original pointers are kept, the latter for calling
free later.
Diffstat (limited to 'elf/dl-tls.c')
-rw-r--r-- | elf/dl-tls.c | 75 |
1 files changed, 46 insertions, 29 deletions
diff --git a/elf/dl-tls.c b/elf/dl-tls.c index ed13fd950b..be6a3c7ef5 100644 --- a/elf/dl-tls.c +++ b/elf/dl-tls.c @@ -494,7 +494,7 @@ _dl_allocate_tls_init (void *result) maxgen = MAX (maxgen, listp->slotinfo[cnt].gen); dtv[map->l_tls_modid].pointer.val = TLS_DTV_UNALLOCATED; - dtv[map->l_tls_modid].pointer.is_static = false; + dtv[map->l_tls_modid].pointer.to_free = NULL; if (map->l_tls_offset == NO_TLS_OFFSET || map->l_tls_offset == FORCED_DYNAMIC_TLS_OFFSET) @@ -551,9 +551,7 @@ _dl_deallocate_tls (void *tcb, bool dealloc_tcb) /* We need to free the memory allocated for non-static TLS. */ for (size_t cnt = 0; cnt < dtv[-1].counter; ++cnt) - if (! dtv[1 + cnt].pointer.is_static - && dtv[1 + cnt].pointer.val != TLS_DTV_UNALLOCATED) - free (dtv[1 + cnt].pointer.val); + free (dtv[1 + cnt].pointer.to_free); /* The array starts with dtv[-1]. */ if (dtv != GL(dl_initial_dtv)) @@ -594,21 +592,49 @@ rtld_hidden_def (_dl_deallocate_tls) # define GET_ADDR_OFFSET ti->ti_offset # endif +/* Allocate one DTV entry. */ +static struct dtv_pointer +allocate_dtv_entry (size_t alignment, size_t size) +{ + if (powerof2 (alignment) && alignment <= _Alignof (max_align_t)) + { + /* The alignment is supported by malloc. */ + void *ptr = malloc (size); + return (struct dtv_pointer) { ptr, ptr }; + } -static void * + /* Emulate memalign to by manually aligning a pointer returned by + malloc. First compute the size with an overflow check. */ + size_t alloc_size = size + alignment; + if (alloc_size < size) + return (struct dtv_pointer) {}; + + /* Perform the allocation. This is the pointer we need to free + later. */ + void *start = malloc (alloc_size); + if (start == NULL) + return (struct dtv_pointer) {}; + + /* Find the aligned position within the larger allocation. */ + void *aligned = (void *) roundup ((uintptr_t) start, alignment); + + return (struct dtv_pointer) { .val = aligned, .to_free = start }; +} + +static struct dtv_pointer allocate_and_init (struct link_map *map) { - void *newp; - - newp = __libc_memalign (map->l_tls_align, map->l_tls_blocksize); - if (newp == NULL) + struct dtv_pointer result = allocate_dtv_entry + (map->l_tls_align, map->l_tls_blocksize); + if (result.val == NULL) oom (); /* Initialize the memory. */ - memset (__mempcpy (newp, map->l_tls_initimage, map->l_tls_initimage_size), + memset (__mempcpy (result.val, map->l_tls_initimage, + map->l_tls_initimage_size), '\0', map->l_tls_blocksize - map->l_tls_initimage_size); - return newp; + return result; } @@ -678,12 +704,9 @@ _dl_update_slotinfo (unsigned long int req_modid) { /* If this modid was used at some point the memory might still be allocated. */ - if (! dtv[total + cnt].pointer.is_static - && (dtv[total + cnt].pointer.val - != TLS_DTV_UNALLOCATED)) - free (dtv[total + cnt].pointer.val); + free (dtv[total + cnt].pointer.to_free); dtv[total + cnt].pointer.val = TLS_DTV_UNALLOCATED; - dtv[total + cnt].pointer.is_static = false; + dtv[total + cnt].pointer.to_free = NULL; } continue; @@ -708,16 +731,9 @@ _dl_update_slotinfo (unsigned long int req_modid) dtv entry free it. */ /* XXX Ideally we will at some point create a memory pool. */ - if (! dtv[modid].pointer.is_static - && dtv[modid].pointer.val != TLS_DTV_UNALLOCATED) - /* Note that free is called for NULL is well. We - deallocate even if it is this dtv entry we are - supposed to load. The reason is that we call - memalign and not malloc. */ - free (dtv[modid].pointer.val); - + free (dtv[modid].pointer.to_free); dtv[modid].pointer.val = TLS_DTV_UNALLOCATED; - dtv[modid].pointer.is_static = false; + dtv[modid].pointer.to_free = NULL; if (modid == req_modid) the_map = map; @@ -780,7 +796,7 @@ tls_get_addr_tail (GET_ADDR_ARGS, dtv_t *dtv, struct link_map *the_map) #endif __rtld_lock_unlock_recursive (GL(dl_load_lock)); - dtv[GET_ADDR_MODULE].pointer.is_static = true; + dtv[GET_ADDR_MODULE].pointer.to_free = NULL; dtv[GET_ADDR_MODULE].pointer.val = p; return (char *) p + GET_ADDR_OFFSET; @@ -788,10 +804,11 @@ tls_get_addr_tail (GET_ADDR_ARGS, dtv_t *dtv, struct link_map *the_map) else __rtld_lock_unlock_recursive (GL(dl_load_lock)); } - void *p = dtv[GET_ADDR_MODULE].pointer.val = allocate_and_init (the_map); - assert (!dtv[GET_ADDR_MODULE].pointer.is_static); + struct dtv_pointer result = allocate_and_init (the_map); + dtv[GET_ADDR_MODULE].pointer = result; + assert (result.to_free != NULL); - return (char *) p + GET_ADDR_OFFSET; + return (char *) result.val + GET_ADDR_OFFSET; } |