Support building for MTE but disabling at runtime when not enabled

include/iso_alloc_ds.h

@@ -152,6 +152,9 @@ typedef struct {
     int32_t big_zone_free_count;
     int32_t big_zone_used_count;
     uint16_t zones_used;
+#if ARM_MTE
+    bool arm_mte_enabled;
+#endif
 } __attribute__((aligned(sizeof(int64_t)))) iso_alloc_root;
 
 typedef struct {

include/iso_alloc_util.h

@@ -25,6 +25,7 @@ INTERNAL_HIDDEN void *create_guard_page(void *p);
 INTERNAL_HIDDEN INLINE void darwin_reuse(void *p, size_t size);
 INTERNAL_HIDDEN void unmap_guarded_pages(void *p, size_t size);
 INTERNAL_HIDDEN ASSUME_ALIGNED void *mmap_guarded_rw_pages(size_t size, bool populate, const char *name);
+INTERNAL_HIDDEN ASSUME_ALIGNED void *mmap_guarded_rw_mte_pages(size_t size, bool populate, const char *name);
 INTERNAL_HIDDEN ASSUME_ALIGNED void *mmap_rw_pages(size_t size, bool populate, const char *name);
 INTERNAL_HIDDEN ASSUME_ALIGNED void *mmap_rw_mte_pages(size_t size, bool populate, const char *name);
 INTERNAL_HIDDEN ASSUME_ALIGNED void *mmap_pages(size_t size, bool populate, const char *name, int32_t prot);

include/os/android.h

@@ -4,6 +4,7 @@
 #pragma once
 
 #include <sys/prctl.h>
+#include <sys/auxv.h>
 
 /* This magic number is usually defined by Android Bionic:
  * https://android.googlesource.com/platform/bionic/+/263325d/libc/include/sys/prctl.h#42 */

include/os/linux.h

@@ -4,6 +4,7 @@
 #pragma once
 
 #include <sys/prctl.h>
+#include <sys/auxv.h>
 #include <byteswap.h>
 /* Get linux kernel version */
 #include <linux/version.h>

src/iso_alloc.c

@@ -69,12 +69,14 @@ INTERNAL_HIDDEN void iso_alloc_initialize_global_root(void) {
 
 #if ARM_MTE
     if(iso_is_mte_supported() == false) {
-        LOG_AND_ABORT("ARM_MTE Enabled in build but not supported by this platform");
+        LOG("ARM_MTE Enabled in build but not supported by this platform");
+        _root->arm_mte_enabled = false;
+    } else {
+        _root->arm_mte_enabled = true;
+        prctl(PR_SET_TAGGED_ADDR_CTRL,
+              PR_TAGGED_ADDR_ENABLE | PR_MTE_TCF_SYNC | (0xfffe << PR_MTE_TAG_SHIFT),
+              0, 0, 0);
     }
-
-    prctl(PR_SET_TAGGED_ADDR_CTRL,
-          PR_TAGGED_ADDR_ENABLE | PR_MTE_TCF_SYNC | (0xfffe << PR_MTE_TAG_SHIFT),
-          0, 0, 0);
 #endif
 
     _root->zone_retirement_shf = _log2(ZONE_ALLOC_RETIRE);
@@ -436,7 +438,17 @@ INTERNAL_HIDDEN iso_alloc_zone_t *_iso_new_zone(size_t size, bool internal, int3
         tag_mapping_size = 0;
     }
 #endif
-    void *p = mmap_rw_pages(total_size, false, name);
+    void *p = NULL;
+
+#if ARM_MTE
+    if(_root->arm_mte_enabled == true) {
+        p = mmap_rw_mte_pages(total_size, false, name);
+    } else {
+        p = mmap_rw_pages(total_size, false, name);
+    }
+#else
+    p = mmap_rw_pages(total_size, false, name);
+#endif
 
 #if(__ANDROID__ || KERNEL_VERSION_SEQ_5_17) && NAMED_MAPPINGS && MEMORY_TAGGING
     if(new_zone->tagged == false) {
@@ -1119,7 +1131,9 @@ INTERNAL_HIDDEN ASSUME_ALIGNED void *_iso_alloc(iso_alloc_zone_t *zone, size_t s
         populate_zone_cache(zone);
 
 #if ARM_MTE
-        p = iso_mte_set_tag_range(p, zone->chunk_size);
+        if(_root->arm_mte_enabled == true) {
+            p = iso_mte_set_tag_range(p, zone->chunk_size);
+        }
 #endif
         return p;
     } else {
@@ -1606,7 +1620,9 @@ INTERNAL_HIDDEN iso_alloc_zone_t *_iso_free_internal_unlocked(void *p, bool perm
 #endif
 
 #if ARM_MTE
-        p = iso_mte_set_tag_range(p, zone->chunk_size);
+        if(_root->arm_mte_enabled == true) {
+            p = iso_mte_set_tag_range(p, zone->chunk_size);
+        }
 #endif
         return zone;
     } else {
@@ -1802,7 +1818,9 @@ INTERNAL_HIDDEN ASSUME_ALIGNED void *_iso_big_alloc(size_t size) {
                 mprotect_pages(big->user_pages_start, big->size, PROT_READ | PROT_WRITE);
 #endif
 #if ARM_MTE
-                big->user_pages_start = iso_mte_set_tag_range(big->user_pages_start, big->size);
+                if(_root->arm_mte_enabled == true) {
+                    big->user_pages_start = iso_mte_set_tag_range(big->user_pages_start, big->size);
+                }
 #endif
                 return big->user_pages_start;
             }
@@ -1822,10 +1840,21 @@ INTERNAL_HIDDEN ASSUME_ALIGNED void *_iso_big_alloc(size_t size) {
 
     /* The free list contained no usable entries
      * so we need to create a new one */
+    void *user_pages = NULL;
+#if ARM_MTE
 #if BIG_ZONE_GUARD
-    void *user_pages = mmap_guarded_rw_pages(size, false, BIG_ZONE_UD_NAME);
+    user_pages = mmap_guarded_rw_pages(size, false, BIG_ZONE_UD_NAME);
 #else
-    void *user_pages = mmap_rw_pages(size, false, BIG_ZONE_UD_NAME);
+    if(_root->arm_mte_enabled == true) {
+        user_pages = mmap_rw_mte_pages(size, false, BIG_ZONE_UD_NAME);
+    }
+#endif
+#else
+#if BIG_ZONE_GUARD
+    user_pages = mmap_guarded_rw_pages(size, false, BIG_ZONE_UD_NAME);
+#else
+    user_pages = mmap_rw_pages(size, false, BIG_ZONE_UD_NAME);
+#endif
 #endif
 
     if(UNLIKELY(user_pages == NULL)) {
@@ -1869,7 +1898,9 @@ INTERNAL_HIDDEN ASSUME_ALIGNED void *_iso_big_alloc(size_t size) {
 
     UNLOCK_BIG_ZONE_USED();
 #if ARM_MTE
-    new_big->user_pages_start = iso_mte_set_tag_range(new_big->user_pages_start, new_big->size);
+    if(_root->arm_mte_enabled == true) {
+        new_big->user_pages_start = iso_mte_set_tag_range(new_big->user_pages_start, new_big->size);
+    }
 #endif
     return new_big->user_pages_start;
 }

src/iso_alloc_mte.c

@@ -2,7 +2,6 @@
  * Copyright 2024 - [email protected] */
 
 #include "iso_alloc_internal.h"
-#include <sys/auxv.h>
 
 /* The majority of this code is adapted from Scudos implementation
  * of ARM MTE support. That code can be found here:

src/iso_alloc_util.c

@@ -76,15 +76,28 @@ void *mmap_guarded_rw_pages(size_t size, bool populate, const char *name) {
         return NULL;
     }
 
+    void *p = mmap_rw_pages(sz + (g_page_size * 2), populate, name);
+
+    create_guard_page(p);
+    create_guard_page(p + (g_page_size + sz));
+    return (p + g_page_size);
+}
+
 #if ARM_MTE
+void *mmap_guarded_rw_mte_pages(size_t size, bool populate, const char *name) {
+    size_t sz = ROUND_UP_PAGE(size);
+
+    if(sz < size) {
+        return NULL;
+    }
+
     void *p = mmap_rw_mte_pages(sz + (g_page_size * 2), populate, name);
-#else
-    void *p = mmap_rw_pages(sz + (g_page_size * 2), populate, name);
-#endif
+
     create_guard_page(p);
     create_guard_page(p + (g_page_size + sz));
     return (p + g_page_size);
 }
+#endif
 
 void *mmap_rw_pages(size_t size, bool populate, const char *name) {
     return mmap_pages(size, populate, name, PROT_READ | PROT_WRITE);