CVE-2022-29694 (published 2022-06-02T14:15Z)

Unicorn Engine v2.0.0-rc7 and below was discovered to contain a NULL pointer dereference via qemu_ram_free.

Severity: MEDIUM
CVSS v2 base score: 5.0 (AV:N/AC:L/Au:N/C:N/I:N/A:P)
CVSS v3 base score: 7.5, HIGH (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

Weakness information:
cwe_id: CWE-476
cwe_name: NULL Pointer Dereference
description: The product dereferences a pointer that it expects to be valid but is NULL.
extended_description: 
            
            
            
         
         

Fix information:
repo_url: https://github.com/unicorn-engine/unicorn
commit_details: repo_url: https://github.com/unicorn-engine/unicorn
author: lazymio
author_date: 2022-04-16 19:17:41+02:00
msg: Fix crash when mapping a big memory and calling uc_close
repository: repo_url: https://github.com/unicorn-engine/unicorn
repo_name: unicorn-engine/unicorn
description: Unicorn CPU emulator framework (ARM, AArch64, M68K, Mips, Sparc, PowerPC, RiscV, S390x, TriCore, X86)
repo_language: C
owner: unicorn-engine
file_changes: filename: exec.c
change_type: ModificationType.MODIFY
diff: @@ -42,7 +42,7 @@
 #include "exec/ram_addr.h"
 
 #include "qemu/range.h"
-
+#include "qemu/rcu_queue.h"
 #include "uc_priv.h"
 
 typedef struct PhysPageEntry PhysPageEntry;
@@ -966,7 +966,7 @@ static ram_addr_t find_ram_offset(struct uc_struct *uc, ram_addr_t size)
 
     assert(size != 0); /* it would hand out same offset multiple times */
 
-    if (QLIST_EMPTY(&uc->ram_list.blocks)) {
+    if (QLIST_EMPTY_RCU(&uc->ram_list.blocks)) {
         return 0;
     }
 
@@ -1043,6 +1043,8 @@ static void ram_block_add(struct uc_struct *uc, RAMBlock *new_block)
         new_block->host = phys_mem_alloc(uc, new_block->max_length,
                 &new_block->mr->align);
         if (!new_block->host) {
+            // mmap fails.
+            uc->invalid_error = UC_ERR_NOMEM;
             // error_setg_errno(errp, errno,
             //         "cannot set up guest memory '%s'",
             //         memory_region_name(new_block->mr));
@@ -1062,11 +1064,11 @@ static void ram_block_add(struct uc_struct *uc, RAMBlock *new_block)
         }
     }
     if (block) {
-        QLIST_INSERT_BEFORE(block, new_block, next);
+        QLIST_INSERT_BEFORE_RCU(block, new_block, next);
     } else if (last_block) {
-        QLIST_INSERT_AFTER(last_block, new_block, next);
+        QLIST_INSERT_AFTER_RCU(last_block, new_block, next);
     } else { /* list is empty */
-        QLIST_INSERT_HEAD(&uc->ram_list.blocks, new_block, next);
+        QLIST_INSERT_HEAD_RCU(&uc->ram_list.blocks, new_block, next);
     }
     uc->ram_list.mru_block = NULL;
 
@@ -1099,8 +1101,15 @@ RAMBlock *qemu_ram_alloc_from_ptr(struct uc_struct *uc, ram_addr_t size, void *h
     if (host) {
         new_block->flags |= RAM_PREALLOC;
     }
+
+    uc->invalid_addr = UC_ERR_OK;
     ram_block_add(mr->uc, new_block);
 
+    if (uc->invalid_error != UC_ERR_OK) {
+        g_free(new_block);
+        return NULL;
+    }
+
     return new_block;
 }
 
@@ -1130,7 +1139,7 @@ void qemu_ram_free(struct uc_struct *uc, RAMBlock *block)
     //    ram_block_notify_remove(block->host, block->max_length);
     //}
 
-    QLIST_REMOVE(block, next);
+    QLIST_REMOVE_RCU(block, next);
     uc->ram_list.mru_block = NULL;
     /* Write list before version */
     //smp_wmb();

programming_language: C
filename: atomic.h
change_type: ModificationType.MODIFY
diff: @@ -115,6 +115,19 @@
     atomic_set__nocheck(ptr, i);                      \
 } while(0)
 
+#define atomic_rcu_read(ptr)                          \
+    ({                                                \
+    QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \
+    typeof_strip_qual(*ptr) _val;                     \
+    atomic_rcu_read__nocheck(ptr, &_val);             \
+    _val;                                             \
+    })
+
+#define atomic_rcu_set(ptr, i) do {                   \
+    QEMU_BUILD_BUG_ON(sizeof(*ptr) > ATOMIC_REG_SIZE); \
+    __atomic_store_n(ptr, i, __ATOMIC_RELEASE);       \
+} while(0)
+
 /* All the remaining operations are fully sequentially consistent */
 
 #define atomic_xchg__nocheck(ptr, i)    ({                  \
@@ -192,6 +205,46 @@
 #define atomic_read(ptr)       atomic_read__nocheck(ptr)
 #define atomic_set(ptr, i)     atomic_set__nocheck(ptr,i)
 
+/**
+ * atomic_rcu_read - reads a RCU-protected pointer to a local variable
+ * into a RCU read-side critical section. The pointer can later be safely
+ * dereferenced within the critical section.
+ *
+ * This ensures that the pointer copy is invariant thorough the whole critical
+ * section.
+ *
+ * Inserts memory barriers on architectures that require them (currently only
+ * Alpha) and documents which pointers are protected by RCU.
+ *
+ * atomic_rcu_read also includes a compiler barrier to ensure that
+ * value-speculative optimizations (e.g. VSS: Value Speculation
+ * Scheduling) does not perform the data read before the pointer read
+ * by speculating the value of the pointer.
+ *
+ * Should match atomic_rcu_set(), atomic_xchg(), atomic_cmpxchg().
+ */
+#define atomic_rcu_read(ptr)    ({                \
+    typeof(*ptr) _val = atomic_read(ptr);         \
+    smp_read_barrier_depends();                   \
+    _val;                                         \
+})
+
+/**
+ * atomic_rcu_set - assigns (publicizes) a pointer to a new data structure
+ * meant to be read by RCU read-side critical sections.
+ *
+ * Documents which pointers will be dereferenced by RCU read-side critical
+ * sections and adds the required memory barriers on architectures requiring
+ * them. It also makes sure the compiler does not reorder code initializing the
+ * data structure before its publication.
+ *
+ * Should match atomic_rcu_read().
+ */
+#define atomic_rcu_set(ptr, i)  do {              \
+    smp_wmb();                                    \
+    atomic_set(ptr, i);                           \
+} while (0)
+
 #define atomic_xchg__nocheck  atomic_xchg
 
 /* Provide shorter names for GCC atomic builtins.  */

programming_language: C
filename: rcu_queue.h
change_type: ModificationType.ADD
diff: @@ -0,0 +1,268 @@
+#ifndef QEMU_RCU_QUEUE_H
+#define QEMU_RCU_QUEUE_H
+
+/*
+ * rcu_queue.h
+ *
+ * RCU-friendly versions of the queue.h primitives.
+ *
+ * This 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.
+ *
+ * This 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 this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * Copyright (c) 2013 Mike D. Day, IBM Corporation.
+ *
+ * IBM's contributions to this file may be relicensed under LGPLv2 or later.
+ */
+
+#include "qemu/queue.h"
+#include "qemu/atomic.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+/*
+ * List access methods.
+ */
+#define QLIST_EMPTY_RCU(head) (atomic_read(&(head)->lh_first) == NULL)
+#define QLIST_FIRST_RCU(head) (atomic_rcu_read(&(head)->lh_first))
+#define QLIST_NEXT_RCU(elm, field) (atomic_rcu_read(&(elm)->field.le_next))
+
+/*
+ * List functions.
+ */
+
+
+/*
+ *  The difference between atomic_read/set and atomic_rcu_read/set
+ *  is in the including of a read/write memory barrier to the volatile
+ *  access. atomic_rcu_* macros include the memory barrier, the
+ *  plain atomic macros do not. Therefore, it should be correct to
+ *  issue a series of reads or writes to the same element using only
+ *  the atomic_* macro, until the last read or write, which should be
+ *  atomic_rcu_* to introduce a read or write memory barrier as
+ *  appropriate.
+ */
+
+/* Upon publication of the listelm->next value, list readers
+ * will see the new node when following next pointers from
+ * antecedent nodes, but may not see the new node when following
+ * prev pointers from subsequent nodes until after the RCU grace
+ * period expires.
+ * see linux/include/rculist.h __list_add_rcu(new, prev, next)
+ */
+#define QLIST_INSERT_AFTER_RCU(listelm, elm, field) do {    \
+    (elm)->field.le_next = (listelm)->field.le_next;        \
+    (elm)->field.le_prev = &(listelm)->field.le_next;       \
+    atomic_rcu_set(&(listelm)->field.le_next, (elm));       \
+    if ((elm)->field.le_next != NULL) {                     \
+       (elm)->field.le_next->field.le_prev =                \
+        &(elm)->field.le_next;                              \
+    }                                                       \
+} while (/*CONSTCOND*/0)
+
+/* Upon publication of the listelm->prev->next value, list
+ * readers will see the new element when following prev pointers
+ * from subsequent elements, but may not see the new element
+ * when following next pointers from antecedent elements
+ * until after the RCU grace period expires.
+ */
+#define QLIST_INSERT_BEFORE_RCU(listelm, elm, field) do {   \
+    (elm)->field.le_prev = (listelm)->field.le_prev;        \
+    (elm)->field.le_next = (listelm);                       \
+    atomic_rcu_set((listelm)->field.le_prev, (elm));        \
+    (listelm)->field.le_prev = &(elm)->field.le_next;       \
+} while (/*CONSTCOND*/0)
+
+/* Upon publication of the head->first value, list readers
+ * will see the new element when following the head, but may
+ * not see the new element when following prev pointers from
+ * subsequent elements until after the RCU grace period has
+ * expired.
+ */
+#define QLIST_INSERT_HEAD_RCU(head, elm, field) do {    \
+    (elm)->field.le_prev = &(head)->lh_first;           \
+    (elm)->field.le_next = (head)->lh_first;            \
+    atomic_rcu_set((&(head)->lh_first), (elm));         \
+    if ((elm)->field.le_next != NULL) {                 \
+       (elm)->field.le_next->field.le_prev =            \
+        &(elm)->field.le_next;                          \
+    }                                                   \
+} while (/*CONSTCOND*/0)
+
+
+/* prior to publication of the elm->prev->next value, some list
+ * readers may still see the removed element when following
+ * the antecedent's next pointer.
+ */
+#define QLIST_REMOVE_RCU(elm, field) do {           \
+    if ((elm)->field.le_next != NULL) {             \
+       (elm)->field.le_next->field.le_prev =        \
+        (elm)->field.le_prev;                       \
+    }                                               \
+    atomic_set((elm)->field.le_prev, (elm)->field.le_next); \
+} while (/*CONSTCOND*/0)
+
+/* List traversal must occur within an RCU critical section.  */
+#define QLIST_FOREACH_RCU(var, head, field)                 \
+        for ((var) = atomic_rcu_read(&(head)->lh_first);    \
+                (var);                                      \
+                (var) = atomic_rcu_read(&(var)->field.le_next))
+
+/* List traversal must occur within an RCU critical section.  */
+#define QLIST_FOREACH_SAFE_RCU(var, head, field, next_var)           \
+    for ((var) = (atomic_rcu_read(&(head)->lh_first));               \
+      (var) &&                                                       \
+          ((next_var) = atomic_rcu_read(&(var)->field.le_next), 1);  \
+           (var) = (next_var))
+
+/*
+ * RCU simple queue
+ */
+
+/* Simple queue access methods */
+#define QSIMPLEQ_EMPTY_RCU(head)      (atomic_read(&(head)->sqh_first) == NULL)
+#define QSIMPLEQ_FIRST_RCU(head)       atomic_rcu_read(&(head)->sqh_first)
+#define QSIMPLEQ_NEXT_RCU(elm, field)  atomic_rcu_read(&(elm)->field.sqe_next)
+
+/* Simple queue functions */
+#define QSIMPLEQ_INSERT_HEAD_RCU(head, elm, field) do {         \
+    (elm)->field.sqe_next = (head)->sqh_first;                  \
+    if ((elm)->field.sqe_next == NULL) {                        \
+        (head)->sqh_last = &(elm)->field.sqe_next;              \
+    }                                                           \
+    atomic_rcu_set(&(head)->sqh_first, (elm));                  \
+} while (/*CONSTCOND*/0)
+
+#define QSIMPLEQ_INSERT_TAIL_RCU(head, elm, field) do {    \
+    (elm)->field.sqe_next = NULL;                          \
+    atomic_rcu_set((head)->sqh_last, (elm));               \
+    (head)->sqh_last = &(elm)->field.sqe_next;             \
+} while (/*CONSTCOND*/0)
+
+#define QSIMPLEQ_INSERT_AFTER_RCU(head, listelm, elm, field) do {       \
+    (elm)->field.sqe_next = (listelm)->field.sqe_next;                  \
+    if ((elm)->field.sqe_next == NULL) {                                \
+        (head)->sqh_last = &(elm)->field.sqe_next;                      \
+    }                                                                   \
+    atomic_rcu_set(&(listelm)->field.sqe_next, (elm));                  \
+} while (/*CONSTCOND*/0)
+
+#define QSIMPLEQ_REMOVE_HEAD_RCU(head, field) do {                     \
+    atomic_set(&(head)->sqh_first, (head)->sqh_first->field.sqe_next); \
+    if ((head)->sqh_first == NULL) {                                   \
+        (head)->sqh_last = &(head)->sqh_first;                         \
+    }                                                                  \
+} while (/*CONSTCOND*/0)
+
+#define QSIMPLEQ_REMOVE_RCU(head, elm, type, field) do {            \
+    if ((head)->sqh_first == (elm)) {                               \
+        QSIMPLEQ_REMOVE_HEAD_RCU((head), field);                    \
+    } else {                                                        \
+        struct type *curr = (head)->sqh_first;                      \
+        while (curr->field.sqe_next != (elm)) {                     \
+            curr = curr->field.sqe_next;                            \
+        }                                                           \
+        atomic_set(&curr->field.sqe_next,                           \
+                   curr->field.sqe_next->field.sqe_next);           \
+        if (curr->field.sqe_next == NULL) {                         \
+            (head)->sqh_last = &(curr)->field.sqe_next;             \
+        }                                                           \
+    }                                                               \
+} while (/*CONSTCOND*/0)
+
+#define QSIMPLEQ_FOREACH_RCU(var, head, field)                          \
+    for ((var) = atomic_rcu_read(&(head)->sqh_first);                   \
+         (var);                                                         \
+         (var) = atomic_rcu_read(&(var)->field.sqe_next))
+
+#define QSIMPLEQ_FOREACH_SAFE_RCU(var, head, field, next)                \
+    for ((var) = atomic_rcu_read(&(head)->sqh_first);                    \
+         (var) && ((next) = atomic_rcu_read(&(var)->field.sqe_next), 1); \
+         (var) = (next))
+
+/*
+ * RCU tail queue
+ */
+
+/* Tail queue access methods */
+#define QTAILQ_EMPTY_RCU(head)      (atomic_read(&(head)->tqh_first) == NULL)
+#define QTAILQ_FIRST_RCU(head)       atomic_rcu_read(&(head)->tqh_first)
+#define QTAILQ_NEXT_RCU(elm, field)  atomic_rcu_read(&(elm)->field.tqe_next)
+
+/* Tail queue functions */
+#define QTAILQ_INSERT_HEAD_RCU(head, elm, field) do {                   \
+    (elm)->field.tqe_next = (head)->tqh_first;                          \
+    if ((elm)->field.tqe_next != NULL) {                                \
+        (head)->tqh_first->field.tqe_circ.tql_prev =                    \
+            &(elm)->field.tqe_circ;                                     \
+    } else {                                                            \
+        (head)->tqh_circ.tql_prev = &(elm)->field.tqe_circ;             \
+    }                                                                   \
+    atomic_rcu_set(&(head)->tqh_first, (elm));                          \
+    (elm)->field.tqe_circ.tql_prev = &(head)->tqh_circ;                 \
+} while (/*CONSTCOND*/0)
+
+#define QTAILQ_INSERT_TAIL_RCU(head, elm, field) do {                   \
+    (elm)->field.tqe_next = NULL;                                       \
+    (elm)->field.tqe_circ.tql_prev = (head)->tqh_circ.tql_prev;         \
+    atomic_rcu_set(&(head)->tqh_circ.tql_prev->tql_next, (elm));        \
+    (head)->tqh_circ.tql_prev = &(elm)->field.tqe_circ;                 \
+} while (/*CONSTCOND*/0)
+
+#define QTAILQ_INSERT_AFTER_RCU(head, listelm, elm, field) do {         \
+    (elm)->field.tqe_next = (listelm)->field.tqe_next;                  \
+    if ((elm)->field.tqe_next != NULL) {                                \
+        (elm)->field.tqe_next->field.tqe_circ.tql_prev =                \
+            &(elm)->field.tqe_circ;                                     \
+    } else {                                                            \
+        (head)->tqh_circ.tql_prev = &(elm)->field.tqe_circ;             \
+    }                                                                   \
+    atomic_rcu_set(&(listelm)->field.tqe_next, (elm));                  \
+    (elm)->field.tqe_circ.tql_prev = &(listelm)->field.tqe_circ;        \
+} while (/*CONSTCOND*/0)
+
+#define QTAILQ_INSERT_BEFORE_RCU(listelm, elm, field) do {                \
+    (elm)->field.tqe_circ.tql_prev = (listelm)->field.tqe_circ.tql_prev;  \
+    (elm)->field.tqe_next = (listelm);                                    \
+    atomic_rcu_set(&(listelm)->field.tqe_circ.tql_prev->tql_next, (elm)); \
+    (listelm)->field.tqe_circ.tql_prev = &(elm)->field.tqe_circ;          \
+} while (/*CONSTCOND*/0)
+
+#define QTAILQ_REMOVE_RCU(head, elm, field) do {                        \
+    if (((elm)->field.tqe_next) != NULL) {                              \
+        (elm)->field.tqe_next->field.tqe_circ.tql_prev =                \
+            (elm)->field.tqe_circ.tql_prev;                             \
+    } else {                                                            \
+        (head)->tqh_circ.tql_prev = (elm)->field.tqe_circ.tql_prev;     \
+    }                                                                   \
+    atomic_set(&(elm)->field.tqe_circ.tql_prev->tql_next, (elm)->field.tqe_next); \
+    (elm)->field.tqe_circ.tql_prev = NULL;                              \
+} while (/*CONSTCOND*/0)
+
+#define QTAILQ_FOREACH_RCU(var, head, field)                            \
+    for ((var) = atomic_rcu_read(&(head)->tqh_first);                   \
+         (var);                                                         \
+         (var) = atomic_rcu_read(&(var)->field.tqe_next))
+
+#define QTAILQ_FOREACH_SAFE_RCU(var, head, field, next)                  \
+    for ((var) = atomic_rcu_read(&(head)->tqh_first);                    \
+         (var) && ((next) = atomic_rcu_read(&(var)->field.tqe_next), 1); \
+         (var) = (next))
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* QEMU_RCU_QUEUE_H */

programming_language: C
filename: memory.c
change_type: ModificationType.MODIFY
diff: @@ -43,8 +43,9 @@ MemoryRegion *memory_map(struct uc_struct *uc, hwaddr begin, size_t size, uint32
     MemoryRegion *ram = g_new(MemoryRegion, 1);
 
     memory_region_init_ram(uc, ram, size, perms);
-    if (ram->addr == -1) {
+    if (ram->addr == -1 || !ram->ram_block) {
         // out of memory
+        g_free(ram);
         return NULL;
     }
 
@@ -63,8 +64,9 @@ MemoryRegion *memory_map_ptr(struct uc_struct *uc, hwaddr begin, size_t size, ui
 
     memory_region_init_ram_ptr(uc, ram, size, ptr);
     ram->perms = perms;
-    if (ram->addr == -1) {
+    if (ram->addr == -1 || !ram->ram_block) {
         // out of memory
+        g_free(ram);
         return NULL;
     }
 

programming_language: C
filename: test_mem.c
change_type: ModificationType.MODIFY
diff: @@ -175,6 +175,18 @@ static void test_map_wrap(void)
     OK(uc_close(uc));
 }
 
+static void test_map_big_memory(void)
+{
+    uc_engine *uc;
+
+    OK(uc_open(UC_ARCH_X86, UC_MODE_64, &uc));
+
+    uc_assert_err(UC_ERR_NOMEM,
+                  uc_mem_map(uc, 0x0, 0xfffffffffffff000, UC_PROT_ALL));
+
+    OK(uc_close(uc));
+}
+
 TEST_LIST = {{"test_map_correct", test_map_correct},
              {"test_map_wrapping", test_map_wrapping},
              {"test_mem_protect", test_mem_protect},
@@ -183,4 +195,5 @@ TEST_LIST = {{"test_map_correct", test_map_correct},
              {"test_mem_protect_map_ptr", test_mem_protect_map_ptr},
              {"test_map_at_the_end", test_map_at_the_end},
              {"test_map_wrap", test_map_wrap},
+             {"test_map_big_memory", test_map_big_memory},
              {NULL, NULL}};

programming_language: C