eu_tfind is used to facilitate lazy loading throughout libdw.
If a result is not found via eu_tfind, work is done to load
the result and cache it in an eu_search_tree.
Some calls to eu_tfind allow for TOCTOU bugs. Multiple threads
might race to call eu_tfind on some result that hasn't yet been
cached. Multiple threads may then attempt to load the result
which might cause an unnecessary amount of memory to be allocated.
Additionally this memory may not get released when the associated
libdw data structure is freed.
Fix this by adding additional locking to ensure that only one
thread performs lazy loading.
One approach used in this patch is to preserve calls to eu_tfind
without additional locking, but when the result isn't found then
a lock is then used to synchronize access to the lazy loading code.
An extra eu_tfind call has been added at the start of these critical
section to synchronize verification that lazy loading should proceed.
Another approach used is to simply synchronize entire calls to
functions where lazy loading via eu_tfind might occur (__libdw_find_fde
and __libdw_intern_expression). In this case, new _nolock variants of
the eu_t* functions are used to avoid unnecessary double locking.
lib/
* eu-search.c: Add eu_tsearch_nolock, eu_tfind_nolock and
eu_tdelete_nolock functions.
* eu-search.h: Ditto.
libdw/
* cfi.h (struct Dwarf_CFI_s): Declare new mutex.
* dwarf_begin_elf.c (valid_p): Initialize all locks for fake CUs.
* dwarf_cfi_addrframe.c (dwarf_cfi_addrframe): Place lock around
__libdw_find_fde.
* dwarf_end.c (cu_free): Deallocate all locks unconditionally,
whether or not the CU is fake.
* dwarf_frame_cfa.c (dwarf_frame_cfa): Place lock around
__libdw_intern_expression.
* dwarf_frame_register.c (dwarf_frame_register): Ditto.
* dwarf_getcfi.c (dwarf_getcfi): Initialize cfi lock.
* dwarf_getlocation.c (is_constant_offset): Synchronize access
to lazy loading section.
(getlocation): Place lock around __libdw_intern_expression.
* dwarf_getmacros.c (cache_op_table): Synchronize access to lazy
loading section.
* frame-cache.c (__libdw_destroy_frame_cache): Free Dwarf_CFI
mutex.
* libdwP.h (struct Dwarf): Update macro_lock comment.
(struct Dwarf_CU): Declare new mutex.
libdw_findcu.c (__libdw_intern_next_unit): Initialize
intern_lock.
(__libdw_findcu): Adjust locking so that the first eu_tfind
can be done without extra lock overhead.
Signed-off-by: Aaron Merey <ame...@redhat.com>
v3:
Implement _nolock functions as inline functions and move to eu-search.h.
Simplify locking in is_constant_offset.
In __libdw_findcu use eu_tfind instead of eu_tfind_nolock.
---
lib/eu-search.h | 24 ++++++++++++++++++++++++
libdw/cfi.h | 4 ++++
libdw/dwarf_begin_elf.c | 15 +++++++++++++++
libdw/dwarf_cfi_addrframe.c | 3 +++
libdw/dwarf_end.c | 10 ++++++----
libdw/dwarf_frame_cfa.c | 2 ++
libdw/dwarf_frame_register.c | 16 ++++++++++------
libdw/dwarf_getcfi.c | 1 +
libdw/dwarf_getlocation.c | 35 ++++++++++++++++++++++-------------
libdw/dwarf_getmacros.c | 20 +++++++++++++++++---
libdw/fde.c | 6 ++++--
libdw/frame-cache.c | 1 +
libdw/libdwP.h | 11 ++++++++---
libdw/libdw_findcu.c | 9 +++++++--
14 files changed, 124 insertions(+), 33 deletions(-)
diff --git a/lib/eu-search.h b/lib/eu-search.h
index 67b54c18..4299e115 100644
--- a/lib/eu-search.h
+++ b/lib/eu-search.h
@@ -52,6 +52,30 @@ extern void *eu_tfind (const void *key, search_tree *tree,
extern void *eu_tdelete (const void *key, search_tree *tree,
int (*compare)(const void *, const void *));
+/* Search TREE for KEY and add KEY if not found. No locking is performed. */
+static inline void *
+eu_tsearch_nolock (const void *key, search_tree *tree,
+ int (*compare)(const void *, const void *))
+{
+ return tsearch (key, &tree->root, compare);
+}
+
+/* Search TREE for KEY. No locking is performed. */
+static inline void *
+eu_tfind_nolock (const void *key, search_tree *tree,
+ int (*compare)(const void *, const void *))
+{
+ return tfind (key, &tree->root, compare);
+}
+
+/* Delete key from TREE. No locking is performed. */
+static inline void *
+eu_tdelete_nolock (const void *key, search_tree *tree,
+ int (*compare)(const void *, const void *))
+{
+ return tdelete (key, &tree->root, compare);
+}
+
/* Free all nodes from TREE. */
void eu_tdestroy (search_tree *tree, void (*free_node)(void *));
diff --git a/libdw/cfi.h b/libdw/cfi.h
index d0134243..f0296de7 100644
--- a/libdw/cfi.h
+++ b/libdw/cfi.h
@@ -98,6 +98,10 @@ struct Dwarf_CFI_s
/* Search tree for parsed DWARF expressions, indexed by raw pointer. */
search_tree expr_tree;
+ /* Should be held when calling __libdw_find_fde, __libdw_fde_by_offset and
+ when __libdw_intern_expression is called with Dwarf_CFI members. */
+ mutex_define(, lock);
+
/* Backend hook. */
struct ebl *ebl;
diff --git a/libdw/dwarf_begin_elf.c b/libdw/dwarf_begin_elf.c
index 58a309e9..63e2805d 100644
--- a/libdw/dwarf_begin_elf.c
+++ b/libdw/dwarf_begin_elf.c
@@ -359,6 +359,11 @@ valid_p (Dwarf *result)
result->fake_loc_cu->version = 4;
result->fake_loc_cu->split = NULL;
eu_search_tree_init (&result->fake_loc_cu->locs_tree);
+ rwlock_init (result->fake_loc_cu->abbrev_lock);
+ rwlock_init (result->fake_loc_cu->split_lock);
+ mutex_init (result->fake_loc_cu->src_lock);
+ mutex_init (result->fake_loc_cu->str_off_base_lock);
+ mutex_init (result->fake_loc_cu->intern_lock);
}
}
@@ -387,6 +392,11 @@ valid_p (Dwarf *result)
result->fake_loclists_cu->version = 5;
result->fake_loclists_cu->split = NULL;
eu_search_tree_init (&result->fake_loclists_cu->locs_tree);
+ rwlock_init (result->fake_loclists_cu->abbrev_lock);
+ rwlock_init (result->fake_loclists_cu->split_lock);
+ mutex_init (result->fake_loclists_cu->src_lock);
+ mutex_init (result->fake_loclists_cu->str_off_base_lock);
+ mutex_init (result->fake_loclists_cu->intern_lock);
}
}
@@ -420,6 +430,11 @@ valid_p (Dwarf *result)
result->fake_addr_cu->version = 5;
result->fake_addr_cu->split = NULL;
eu_search_tree_init (&result->fake_addr_cu->locs_tree);
+ rwlock_init (result->fake_addr_cu->abbrev_lock);
+ rwlock_init (result->fake_addr_cu->split_lock);
+ mutex_init (result->fake_addr_cu->src_lock);
+ mutex_init (result->fake_addr_cu->str_off_base_lock);
+ mutex_init (result->fake_addr_cu->intern_lock);
}
}
diff --git a/libdw/dwarf_cfi_addrframe.c b/libdw/dwarf_cfi_addrframe.c
index 44240279..f391f9f9 100644
--- a/libdw/dwarf_cfi_addrframe.c
+++ b/libdw/dwarf_cfi_addrframe.c
@@ -39,7 +39,10 @@ dwarf_cfi_addrframe (Dwarf_CFI *cache, Dwarf_Addr address,
Dwarf_Frame **frame)
if (cache == NULL)
return -1;
+ mutex_lock (cache->lock);
struct dwarf_fde *fde = __libdw_find_fde (cache, address);
+ mutex_unlock (cache->lock);
+
if (fde == NULL)
return -1;
diff --git a/libdw/dwarf_end.c b/libdw/dwarf_end.c
index 1628e448..979b1168 100644
--- a/libdw/dwarf_end.c
+++ b/libdw/dwarf_end.c
@@ -61,17 +61,19 @@ static void
cu_free (void *arg)
{
struct Dwarf_CU *p = (struct Dwarf_CU *) arg;
+
eu_search_tree_fini (&p->locs_tree, noop_free);
+ rwlock_fini (p->abbrev_lock);
+ rwlock_fini (p->split_lock);
+ mutex_fini (p->src_lock);
+ mutex_fini (p->str_off_base_lock);
+ mutex_fini (p->intern_lock);
/* Only free the CU internals if its not a fake CU. */
if (p != p->dbg->fake_loc_cu && p != p->dbg->fake_loclists_cu
&& p != p->dbg->fake_addr_cu)
{
Dwarf_Abbrev_Hash_free (&p->abbrev_hash);
- rwlock_fini (p->abbrev_lock);
- rwlock_fini (p->split_lock);
- mutex_fini (p->src_lock);
- mutex_fini (p->str_off_base_lock);
/* Free split dwarf one way (from skeleton to split). */
if (p->unit_type == DW_UT_skeleton
diff --git a/libdw/dwarf_frame_cfa.c b/libdw/dwarf_frame_cfa.c
index 07f998cd..c18ee499 100644
--- a/libdw/dwarf_frame_cfa.c
+++ b/libdw/dwarf_frame_cfa.c
@@ -57,11 +57,13 @@ dwarf_frame_cfa (Dwarf_Frame *fs, Dwarf_Op **ops, size_t
*nops)
case cfa_expr:
/* Parse the expression into internal form. */
+ mutex_lock (fs->cache->lock);
result = __libdw_intern_expression
(NULL, fs->cache->other_byte_order,
fs->cache->e_ident[EI_CLASS] == ELFCLASS32 ? 4 : 8, 4,
&fs->cache->expr_tree, &fs->cfa_data.expr, false, false,
ops, nops, IDX_debug_frame);
+ mutex_unlock (fs->cache->lock);
break;
case cfa_invalid:
diff --git a/libdw/dwarf_frame_register.c b/libdw/dwarf_frame_register.c
index a6b7c4c1..dbd7f1b2 100644
--- a/libdw/dwarf_frame_register.c
+++ b/libdw/dwarf_frame_register.c
@@ -109,12 +109,16 @@ dwarf_frame_register (Dwarf_Frame *fs, int regno,
Dwarf_Op ops_mem[3],
block.data = (void *) p;
/* Parse the expression into internal form. */
- if (__libdw_intern_expression (NULL,
- fs->cache->other_byte_order,
- address_size, 4,
- &fs->cache->expr_tree, &block,
- true, reg->rule == reg_val_expression,
- ops, nops, IDX_debug_frame) < 0)
+ mutex_lock (fs->cache->lock);
+ int res = __libdw_intern_expression (NULL,
+ fs->cache->other_byte_order,
+ address_size, 4,
+ &fs->cache->expr_tree, &block,
+ true, reg->rule ==
reg_val_expression,
+ ops, nops, IDX_debug_frame);
+ mutex_unlock (fs->cache->lock);
+
+ if (res < 0)
return -1;
break;
}
diff --git a/libdw/dwarf_getcfi.c b/libdw/dwarf_getcfi.c
index a4497152..893e3c74 100644
--- a/libdw/dwarf_getcfi.c
+++ b/libdw/dwarf_getcfi.c
@@ -70,6 +70,7 @@ dwarf_getcfi (Dwarf *dbg)
eu_search_tree_init (&cfi->cie_tree);
eu_search_tree_init (&cfi->fde_tree);
eu_search_tree_init (&cfi->expr_tree);
+ mutex_init (cfi->lock);
cfi->ebl = NULL;
diff --git a/libdw/dwarf_getlocation.c b/libdw/dwarf_getlocation.c
index ad1d46ca..6d7296f8 100644
--- a/libdw/dwarf_getlocation.c
+++ b/libdw/dwarf_getlocation.c
@@ -154,7 +154,7 @@ store_implicit_value (Dwarf *dbg, search_tree *cache,
Dwarf_Op *op)
block->addr = op;
block->data = (unsigned char *) data;
block->length = op->number;
- if (unlikely (eu_tsearch (block, cache, loc_compare) == NULL))
+ if (unlikely (eu_tsearch_nolock (block, cache, loc_compare) == NULL))
return 1;
return 0;
}
@@ -211,14 +211,18 @@ is_constant_offset (Dwarf_Attribute *attr,
}
/* Check whether we already cached this location. */
+ mutex_lock (attr->cu->intern_lock);
struct loc_s fake = { .addr = attr->valp };
- struct loc_s **found = eu_tfind (&fake, &attr->cu->locs_tree, loc_compare);
+ struct loc_s **found = eu_tfind_nolock (&fake, &attr->cu->locs_tree,
loc_compare);
if (found == NULL)
{
Dwarf_Word offset;
if (INTUSE(dwarf_formudata) (attr, &offset) != 0)
- return -1;
+ {
+ mutex_unlock (attr->cu->intern_lock);
+ return -1;
+ }
Dwarf_Op *result = libdw_alloc (attr->cu->dbg,
Dwarf_Op, sizeof (Dwarf_Op), 1);
@@ -236,9 +240,10 @@ is_constant_offset (Dwarf_Attribute *attr,
newp->loc = result;
newp->nloc = 1;
- found = eu_tsearch (newp, &attr->cu->locs_tree, loc_compare);
+ found = eu_tsearch_nolock (newp, &attr->cu->locs_tree, loc_compare);
}
+ mutex_unlock (attr->cu->intern_lock);
assert ((*found)->nloc == 1);
if (llbuf != NULL)
@@ -267,7 +272,7 @@ __libdw_intern_expression (Dwarf *dbg, bool
other_byte_order,
/* Check whether we already looked at this list. */
struct loc_s fake = { .addr = block->data };
- struct loc_s **found = eu_tfind (&fake, cache, loc_compare);
+ struct loc_s **found = eu_tfind_nolock (&fake, cache, loc_compare);
if (found != NULL)
{
/* We already saw it. */
@@ -656,7 +661,7 @@ __libdw_intern_expression (Dwarf *dbg, bool
other_byte_order,
newp->addr = block->data;
newp->loc = result;
newp->nloc = *listlen;
- eu_tsearch (newp, cache, loc_compare);
+ eu_tsearch_nolock (newp, cache, loc_compare);
/* We did it. */
return 0;
@@ -674,13 +679,17 @@ getlocation (struct Dwarf_CU *cu, const Dwarf_Block
*block,
return 0;
}
- return __libdw_intern_expression (cu->dbg, cu->dbg->other_byte_order,
- cu->address_size, (cu->version == 2
- ? cu->address_size
- : cu->offset_size),
- &cu->locs_tree, block,
- false, false,
- llbuf, listlen, sec_index);
+ mutex_lock (cu->intern_lock);
+ int res = __libdw_intern_expression (cu->dbg, cu->dbg->other_byte_order,
+ cu->address_size, (cu->version == 2
+ ? cu->address_size
+ : cu->offset_size),
+ &cu->locs_tree, block,
+ false, false,
+ llbuf, listlen, sec_index);
+ mutex_unlock (cu->intern_lock);
+
+ return res;
}
int
diff --git a/libdw/dwarf_getmacros.c b/libdw/dwarf_getmacros.c
index f1c831fa..d7ed7b58 100644
--- a/libdw/dwarf_getmacros.c
+++ b/libdw/dwarf_getmacros.c
@@ -322,15 +322,29 @@ cache_op_table (Dwarf *dbg, int sec_index, Dwarf_Off
macoff,
if (found != NULL)
return *found;
+ mutex_lock (dbg->macro_lock);
+
+ found = eu_tfind_nolock (&fake, &dbg->macro_ops_tree, macro_op_compare);
+ if (found != NULL)
+ {
+ mutex_unlock (dbg->macro_lock);
+ return *found;
+ }
+
Dwarf_Macro_Op_Table *table = sec_index == IDX_debug_macro
? get_table_for_offset (dbg, macoff, startp, endp, cudie)
: get_macinfo_table (dbg, macoff, cudie);
if (table == NULL)
- return NULL;
+ {
+ mutex_unlock (dbg->macro_lock);
+ return NULL;
+ }
+
+ Dwarf_Macro_Op_Table **ret = eu_tsearch_nolock (table, &dbg->macro_ops_tree,
+ macro_op_compare);
+ mutex_unlock (dbg->macro_lock);
- Dwarf_Macro_Op_Table **ret = eu_tsearch (table, &dbg->macro_ops_tree,
- macro_op_compare);
if (unlikely (ret == NULL))
{
__libdw_seterrno (DWARF_E_NOMEM);
diff --git a/libdw/fde.c b/libdw/fde.c
index a5167805..7f36c4a9 100644
--- a/libdw/fde.c
+++ b/libdw/fde.c
@@ -122,7 +122,8 @@ intern_fde (Dwarf_CFI *cache, const Dwarf_FDE *entry)
fde->instructions += cie->fde_augmentation_data_size;
/* Add the new entry to the search tree. */
- struct dwarf_fde **tres = eu_tsearch (fde, &cache->fde_tree, &compare_fde);
+ struct dwarf_fde **tres = eu_tsearch_nolock (fde, &cache->fde_tree,
+ &compare_fde);
if (tres == NULL)
{
free (fde);
@@ -252,7 +253,8 @@ __libdw_find_fde (Dwarf_CFI *cache, Dwarf_Addr address)
/* Look for a cached FDE covering this address. */
const struct dwarf_fde fde_key = { .start = address, .end = 0 };
- struct dwarf_fde **found = eu_tfind (&fde_key, &cache->fde_tree,
&compare_fde);
+ struct dwarf_fde **found = eu_tfind_nolock (&fde_key, &cache->fde_tree,
+ &compare_fde);
if (found != NULL)
return *found;
diff --git a/libdw/frame-cache.c b/libdw/frame-cache.c
index 6c89858a..6f6f777e 100644
--- a/libdw/frame-cache.c
+++ b/libdw/frame-cache.c
@@ -64,6 +64,7 @@ __libdw_destroy_frame_cache (Dwarf_CFI *cache)
eu_search_tree_fini (&cache->fde_tree, free_fde);
eu_search_tree_fini (&cache->cie_tree, free_cie);
eu_search_tree_fini (&cache->expr_tree, free_expr);
+ mutex_fini (cache->lock);
if (cache->ebl != NULL && cache->ebl != (void *) -1l)
ebl_closebackend (cache->ebl);
diff --git a/libdw/libdwP.h b/libdw/libdwP.h
index de80cd4e..25d53d31 100644
--- a/libdw/libdwP.h
+++ b/libdw/libdwP.h
@@ -269,7 +269,7 @@ struct Dwarf
__libdw_intern_next_unit. */
mutex_define(, dwarf_lock);
- /* Synchronize access to dwarf_macro_getsrcfiles. */
+ /* Synchronize access to dwarf_macro_getsrcfiles and cache_op_table. */
mutex_define(, macro_lock);
/* Internal memory handling. This is basically a simplified thread-local
@@ -471,6 +471,10 @@ struct Dwarf_CU
Covers __libdw_str_offsets_base_off. */
mutex_define(, str_off_base_lock);
+ /* Synchronize access to is_constant_offset. Should also be held
+ when calling __libdw_intern_expression with Dwarf_CU members. */
+ mutex_define(, intern_lock);
+
/* Memory boundaries of this CU. */
void *startp;
void *endp;
@@ -949,8 +953,9 @@ extern int __libdw_visit_scopes (unsigned int depth,
void *arg)
__nonnull_attribute__ (2, 4) internal_function;
-/* Parse a DWARF Dwarf_Block into an array of Dwarf_Op's,
- and cache the result (via tsearch). */
+/* Parse a DWARF Dwarf_Block into an array of Dwarf_Op's, and cache the
+ result (via tsearch). The owner of CACHE (typically a Dwarf_CU or
+ Dwarf_CFI_s) must hold a lock when calling this function. */
extern int __libdw_intern_expression (Dwarf *dbg,
bool other_byte_order,
unsigned int address_size,
diff --git a/libdw/libdw_findcu.c b/libdw/libdw_findcu.c
index 0e4dcc37..59267343 100644
--- a/libdw/libdw_findcu.c
+++ b/libdw/libdw_findcu.c
@@ -181,6 +181,7 @@ __libdw_intern_next_unit (Dwarf *dbg, bool debug_types)
rwlock_init (newp->split_lock);
mutex_init (newp->src_lock);
mutex_init (newp->str_off_base_lock);
+ mutex_init (newp->intern_lock);
/* v4 debug type units have version == 4 and unit_type == DW_UT_type. */
if (debug_types)
@@ -240,8 +241,6 @@ struct Dwarf_CU *
internal_function
__libdw_findcu (Dwarf *dbg, Dwarf_Off start, bool v4_debug_types)
{
- mutex_lock (dbg->dwarf_lock);
-
search_tree *tree = v4_debug_types ? &dbg->tu_tree : &dbg->cu_tree;
Dwarf_Off *next_offset
= v4_debug_types ? &dbg->next_tu_offset : &dbg->next_cu_offset;
@@ -250,6 +249,12 @@ __libdw_findcu (Dwarf *dbg, Dwarf_Off start, bool
v4_debug_types)
struct Dwarf_CU fake = { .start = start, .end = 0 };
struct Dwarf_CU **found = eu_tfind (&fake, tree, findcu_cb);
struct Dwarf_CU *result = NULL;
+ if (found != NULL)
+ return *found;
+
+ mutex_lock (dbg->dwarf_lock);
+
+ found = eu_tfind (&fake, tree, findcu_cb);
if (found != NULL)
{
mutex_unlock (dbg->dwarf_lock);
--
2.49.0
