diff --git a/features/FEATURE_UVISOR/AUTHORS.txt b/features/FEATURE_UVISOR/AUTHORS.txt
index b6cbc9070d..597762e4a7 100644
--- a/features/FEATURE_UVISOR/AUTHORS.txt
+++ b/features/FEATURE_UVISOR/AUTHORS.txt
@@ -1,7 +1,7 @@
-   552	Milosch Meriac
-   457	Alessandro Angelino
+   553	Milosch Meriac
+   458	Alessandro Angelino
+    42	Niklas Hauser
     40	Jaeden Amero
-    31	Niklas Hauser
      3	Hugo Vincent
      3	JaredCJR
      3	Jim Huang
diff --git a/features/FEATURE_UVISOR/VERSION.txt b/features/FEATURE_UVISOR/VERSION.txt
index 1f0020a9d5..c9de7074f5 100644
--- a/features/FEATURE_UVISOR/VERSION.txt
+++ b/features/FEATURE_UVISOR/VERSION.txt
@@ -1 +1 @@
-v0.20.1-alpha
+v0.21.0-alpha
diff --git a/features/FEATURE_UVISOR/includes/uvisor/api/inc/box_config.h b/features/FEATURE_UVISOR/includes/uvisor/api/inc/box_config.h
index 1a076d806c..a15295daf3 100644
--- a/features/FEATURE_UVISOR/includes/uvisor/api/inc/box_config.h
+++ b/features/FEATURE_UVISOR/includes/uvisor/api/inc/box_config.h
@@ -18,6 +18,7 @@
 #define __UVISOR_API_BOX_CONFIG_H__
 
 #include "api/inc/uvisor_exports.h"
+#include "api/inc/page_allocator_exports.h"
 #include <stddef.h>
 #include <stdint.h>
 
@@ -53,6 +54,14 @@ UVISOR_EXTERN const uint32_t __uvisor_mode;
     \
     extern const __attribute__((section(".keep.uvisor.cfgtbl_ptr_first"), aligned(4))) void * const main_cfg_ptr = &main_cfg;
 
+/* Creates a global page heap with at least `minimum_number_of_pages` each of size `page_size` in bytes.
+ * The total page heap size is at least `minimum_number_of_pages * page_size`. */
+#define UVISOR_SET_PAGE_HEAP(page_size, minimum_number_of_pages) \
+    const uint32_t __uvisor_page_size = (page_size); \
+    uint8_t __attribute__((section(".keep.uvisor.page_heap"))) \
+        main_page_heap_reserved[ (page_size) * (minimum_number_of_pages) ]
+
+
 /* this macro selects an overloaded macro (variable number of arguments) */
 #define __UVISOR_BOX_MACRO(_1, _2, _3, _4, NAME, ...) NAME
 
diff --git a/features/FEATURE_UVISOR/includes/uvisor/api/inc/page_allocator.h b/features/FEATURE_UVISOR/includes/uvisor/api/inc/page_allocator.h
index 56cff28d13..7dae4b694f 100644
--- a/features/FEATURE_UVISOR/includes/uvisor/api/inc/page_allocator.h
+++ b/features/FEATURE_UVISOR/includes/uvisor/api/inc/page_allocator.h
@@ -34,4 +34,7 @@ UVISOR_EXTERN int uvisor_page_malloc(UvisorPageTable * const table);
  */
 UVISOR_EXTERN int uvisor_page_free(const UvisorPageTable * const table);
 
+/* @returns the active page size for one page. */
+UVISOR_EXTERN uint32_t uvisor_get_page_size(void);
+
 #endif /* __UVISOR_API_PAGE_ALLOCATOR_H__ */
diff --git a/features/FEATURE_UVISOR/includes/uvisor/api/inc/page_allocator_exports.h b/features/FEATURE_UVISOR/includes/uvisor/api/inc/page_allocator_exports.h
index 89ee998d97..52c24ec925 100644
--- a/features/FEATURE_UVISOR/includes/uvisor/api/inc/page_allocator_exports.h
+++ b/features/FEATURE_UVISOR/includes/uvisor/api/inc/page_allocator_exports.h
@@ -30,27 +30,9 @@
 #define UVISOR_ERROR_PAGE_INVALID_PAGE_OWNER    (UVISOR_ERROR_CLASS_PAGE + 5)
 #define UVISOR_ERROR_PAGE_INVALID_PAGE_COUNT    (UVISOR_ERROR_CLASS_PAGE + 6)
 
-
-/* Must be a power of 2 for MPU alignment in ARMv7-M with ARM MPU.
- * Must be multiple of 32 for K64F MPU. */
-#ifndef UVISOR_PAGE_SIZE
-#define UVISOR_PAGE_SIZE ((uint32_t) 16 * 1024)
-#endif
-
-/* Return the rounded up number of pages required to hold `size`. */
-#define UVISOR_PAGES_FOR_SIZE(size) ((size + UVISOR_PAGE_SIZE - 1) / UVISOR_PAGE_SIZE)
-
-/* Create a page table with `count` many entries. */
-#define UVISOR_PAGE_TABLE(count) \
-    struct { \
-        uint32_t page_size; \
-        uint32_t page_count; \
-        void * page_origins[count]; \
-    }
-
-/* Create a page table with enough pages to hold `size`. */
-#define UVISOR_PAGE_TABLE_FOR_SIZE(size) UVISOR_PAGE_TABLE(UVISOR_PAGES_FOR_SIZE(size))
-
+/* Contains the uVisor page size.
+ * @warning Do not read directly, instead use `uvisor_get_page_size()` accessor! */
+UVISOR_EXTERN const uint32_t __uvisor_page_size;
 
 typedef struct {
     uint32_t page_size;     /* The page size in bytes. Must be multiple of `UVISOR_PAGE_SIZE`! */
diff --git a/features/FEATURE_UVISOR/source/page_allocator.c_inc b/features/FEATURE_UVISOR/source/page_allocator.c_inc
index 1f4e7efb0c..7373fd5d5f 100644
--- a/features/FEATURE_UVISOR/source/page_allocator.c_inc
+++ b/features/FEATURE_UVISOR/source/page_allocator.c_inc
@@ -41,8 +41,10 @@
 
 #include "page_allocator_config.h"
 
-/* Maps the page to the owning box handle. */
-page_owner_t g_page_owner_table[UVISOR_PAGE_TABLE_MAX_COUNT];
+/* Contains the page usage mapped by owner. */
+uint32_t g_page_owner_map[UVISOR_MAX_BOXES][UVISOR_PAGE_MAP_COUNT];
+/* Contains total page usage. */
+uint32_t g_page_usage_map[UVISOR_PAGE_MAP_COUNT];
 /* Contains the configured page size. */
 uint32_t g_page_size;
 /* Points to the beginning of the page heap. */
@@ -119,12 +121,16 @@ void page_allocator_init(void * const heap_start, void * const heap_end, const u
         g_page_count_total = ((uint32_t) heap_end - start) / g_page_size;
     }
     /* Clamp page count to table size. */
-    if (g_page_count_total > UVISOR_PAGE_TABLE_MAX_COUNT) {
-        g_page_count_total = UVISOR_PAGE_TABLE_MAX_COUNT;
+    if (g_page_count_total > UVISOR_PAGE_MAX_COUNT) {
+        DPRINTF("uvisor_page_init: Clamping available page count from %u to %u!\n", g_page_count_total, UVISOR_PAGE_MAX_COUNT);
+        /* Move the heap start address forward so that the last clamped page is located nearest to the heap end. */
+        g_page_heap_start += (g_page_count_total - UVISOR_PAGE_MAX_COUNT) * g_page_size;
+        /* Clamp the page count. */
+        g_page_count_total = UVISOR_PAGE_MAX_COUNT;
     }
     g_page_count_free = g_page_count_total;
     /* Remember the end of the heap. */
-    g_page_heap_end = g_page_heap_start + g_page_count_free * g_page_size;
+    g_page_heap_end = g_page_heap_start + g_page_count_total * g_page_size;
 
     DPRINTF("uvisor_page_init:\n.page_heap start 0x%08x\n.page_heap end   0x%08x\n.page_heap available %ukB split into %u pages of %ukB\n\n",
             (unsigned int) g_page_heap_start,
@@ -133,11 +139,9 @@ void page_allocator_init(void * const heap_start, void * const heap_end, const u
             (unsigned int) g_page_count_total,
             (unsigned int) (g_page_size / 1024));
 
-    uint32_t page = 0;
-    for (; page < UVISOR_PAGE_TABLE_MAX_COUNT; page++) {
-        g_page_owner_table[page] = UVISOR_PAGE_UNUSED;
-        page_allocator_reset_faults(page);
-    }
+    /* Force a reset of owner and usage page maps. */
+    memset(g_page_owner_map, 0, sizeof(g_page_owner_map));
+    memset(g_page_usage_map, 0, sizeof(g_page_usage_map));
 }
 
 int page_allocator_malloc(UvisorPageTable * const table)
@@ -176,10 +180,20 @@ int page_allocator_malloc(UvisorPageTable * const table)
     /* Iterate through the page table and find the empty pages. */
     uint32_t page = 0;
     for (; (page < g_page_count_total) && pages_required; page++) {
-        /* If the page is unused, it's entry is UVISOR_PAGE_UNUSED (not NULL!). */
-        if (g_page_owner_table[page] == UVISOR_PAGE_UNUSED) {
-            /* Marry this page to the box id. */
-            g_page_owner_table[page] = box_id;
+        /* If the page is unused, map_get returns zero. */
+        if (!page_allocator_map_get(g_page_usage_map, page)) {
+            /* Remember this page as used. */
+            page_allocator_map_set(g_page_usage_map, page);
+            /* Pages of box 0 are accessible to all other boxes! */
+            if (box_id == 0) {
+                uint32_t ii = 0;
+                for (; ii < UVISOR_MAX_BOXES; ii++) {
+                    page_allocator_map_set(g_page_owner_map[ii], page);
+                }
+            } else {
+                /* Otherwise, remember ownership only for active box. */
+                page_allocator_map_set(g_page_owner_map[box_id], page);
+            }
             /* Reset the fault count for this page. */
             page_allocator_reset_faults(page);
             /* Get the pointer to the page. */
@@ -243,14 +257,25 @@ int page_allocator_free(const UvisorPageTable * const table)
             return UVISOR_ERROR_PAGE_INVALID_PAGE_ORIGIN;
         }
         /* Check if the page belongs to the caller. */
-        if (g_page_owner_table[page_index] == box_id) {
-            g_page_owner_table[page_index] = UVISOR_PAGE_UNUSED;
+        if (page_allocator_map_get(g_page_owner_map[box_id], page_index)) {
+            /* Clear the owner and usage page maps for this page. */
+            page_allocator_map_clear(g_page_usage_map, page_index);
+            /* If the page was owned by box 0, we need to remove it from all other boxes! */
+            if (box_id == 0) {
+                uint32_t ii = 0;
+                for (; ii < UVISOR_MAX_BOXES; ii++) {
+                    page_allocator_map_clear(g_page_owner_map[ii], page_index);
+                }
+            } else {
+                /* Otherwise, only remove for the active box. */
+                page_allocator_map_clear(g_page_owner_map[box_id], page_index);
+            }
             g_page_count_free++;
             DPRINTF("uvisor_page_free: Freeing page at index %u\n", page_index);
         }
         else {
             /* Abort if the page doesn't belong to the caller. */
-            if (g_page_owner_table[page_index] == UVISOR_PAGE_UNUSED) {
+            if (!page_allocator_map_get(g_page_usage_map, page_index)) {
                 DPRINTF("uvisor_page_free: FAIL: Page %u is not allocated!\n\n", page_index);
             } else {
                 DPRINTF("uvisor_page_free: FAIL: Page %u is not owned by box %u!\n\n", page_index, box_id);
diff --git a/features/FEATURE_UVISOR/source/page_allocator_config.h b/features/FEATURE_UVISOR/source/page_allocator_config.h
index 27f1a43d90..f72ec67514 100644
--- a/features/FEATURE_UVISOR/source/page_allocator_config.h
+++ b/features/FEATURE_UVISOR/source/page_allocator_config.h
@@ -25,8 +25,8 @@
  * a relatively low limit to the number of pages.
  * By default a maximum of 16 pages are allowed. This can only be overwritten
  * by the porting engineer for the current platform. */
-#ifndef UVISOR_PAGE_TABLE_MAX_COUNT
-#define UVISOR_PAGE_TABLE_MAX_COUNT ((uint32_t) 16)
+#ifndef UVISOR_PAGE_MAX_COUNT
+#define UVISOR_PAGE_MAX_COUNT (16UL)
 #endif
 /* The number of pages is decided by the page size. A small page size leads to
  * a lot of pages, however, number of pages is capped for efficiency.
@@ -34,12 +34,49 @@
  * will lead to allocation failures. This can only be overwritten
  * by the porting engineer for the current platform. */
 #ifndef UVISOR_PAGE_SIZE_MINIMUM
-#define UVISOR_PAGE_SIZE_MINIMUM ((uint32_t) 1024)
+#define UVISOR_PAGE_SIZE_MINIMUM (1024UL)
 #endif
 
+/* Defines the number of uint32_t page owner masks in the owner map. */
+#define UVISOR_PAGE_MAP_COUNT ((UVISOR_PAGE_MAX_COUNT + 31) / 32)
+
 /* The page box_id is the box id which is 8-bit large. */
 typedef uint8_t page_owner_t;
 /* Define a unused value for the page table. */
 #define UVISOR_PAGE_UNUSED ((page_owner_t) (-1))
+/* Contains the total number of available pages. */
+extern uint8_t g_page_count_total;
+
+/** Sets the page bit in the page map array.
+ * @param map   an array of `uint32_t` containing the page map
+ * @param page  the index of the page to be set
+ */
+static inline void page_allocator_map_set(uint32_t * const map, uint8_t page)
+{
+    page += UVISOR_PAGE_MAP_COUNT * 32 - g_page_count_total;
+    map[page / 32] |= (1UL << (page % 32));
+}
+
+/** Clears the page bit in the page map array.
+ * @param map   an array of `uint32_t` containing the page map
+ * @param page  the index of the page to be set
+ */
+static inline void page_allocator_map_clear(uint32_t * const map, uint8_t page)
+{
+    page += UVISOR_PAGE_MAP_COUNT * 32 - g_page_count_total;
+    map[page / 32] &= ~(1UL << (page % 32));
+}
+
+/** Check if the page bit is set int the page map array.
+ * @param map   an array of `uint32_t` containing the page map
+ * @param page  the index of the page to be set
+ * @retval 0    if page bit is not set
+ * @retval 1    if page bit is set
+ */
+static inline int page_allocator_map_get(const uint32_t * const map, uint8_t page)
+{
+    page += UVISOR_PAGE_MAP_COUNT * 32 - g_page_count_total;
+    return (map[page / 32] >> (page % 32)) & 0x1;
+}
 
 #endif /* __PAGE_ALLOCATOR_CONFIG_H__ */
diff --git a/features/FEATURE_UVISOR/source/rtx/secure_allocator.c b/features/FEATURE_UVISOR/source/rtx/secure_allocator.c
index 10b6214d8b..c40e3890a2 100644
--- a/features/FEATURE_UVISOR/source/rtx/secure_allocator.c
+++ b/features/FEATURE_UVISOR/source/rtx/secure_allocator.c
@@ -32,10 +32,6 @@
 /* offsetof is a gcc built-in function, this is the manual implementation */
 #define OFFSETOF(type, member) ((uint32_t) (&(((type *)(0))->member)))
 
-/* Declare this variable here, so the tier-2 allocator _always_ uses the
- * page size that the tier-1 allocator expects! */
-const uint32_t __uvisor_page_size = UVISOR_PAGE_SIZE;
-
 /* Internal structure currently only contains the page table. */
 typedef struct {
     UvisorPageTable table;
@@ -71,10 +67,11 @@ SecureAllocator secure_allocator_create_with_pages(
     size_t size,
     size_t maximum_malloc_size)
 {
+    const uint32_t page_size = uvisor_get_page_size();
     /* The rt_Memory allocator puts one MEMP structure at both the
      * beginning and end of the memory pool. */
     const size_t block_overhead = 2 * sizeof(MEMP);
-    const size_t page_size_with_overhead = UVISOR_PAGE_SIZE + block_overhead;
+    const size_t page_size_with_overhead = page_size + block_overhead;
     /* Calculate the integer part of required the page count. */
     size_t page_count = size / page_size_with_overhead;
     /* Add another page if the remainder is not zero. */
@@ -84,7 +81,7 @@ SecureAllocator secure_allocator_create_with_pages(
     DPRINTF("secure_allocator_create_with_pages: Requesting %u pages for at least %uB\n", page_count, size);
 
     /* Compute the maximum allocation within our blocks. */
-    size_t maximum_allocation_size = UVISOR_PAGE_SIZE - block_overhead;
+    size_t maximum_allocation_size = page_size - block_overhead;
     /* If the required maximum allocation is larger than we can provide, abort. */
     if (maximum_malloc_size > maximum_allocation_size) {
         DPRINTF("secure_allocator_create_with_pages: Maximum allocation request %uB is larger then available %uB\n\n", maximum_malloc_size, maximum_allocation_size);
@@ -104,7 +101,7 @@ SecureAllocator secure_allocator_create_with_pages(
     }
 
     /* Prepare the page table. */
-    allocator->table.page_size = UVISOR_PAGE_SIZE;
+    allocator->table.page_size = page_size;
     allocator->table.page_count = page_count;
     /* Get me some pages. */
     if (uvisor_page_malloc((UvisorPageTable *) &(allocator->table))) {
@@ -116,7 +113,7 @@ SecureAllocator secure_allocator_create_with_pages(
     /* Initialize a MEMP structure in all pages. */
     for(size_t ii = 0; ii < page_count; ii++) {
         /* Add each page as a pool. */
-        rt_init_mem(allocator->table.page_origins[ii], UVISOR_PAGE_SIZE);
+        rt_init_mem(allocator->table.page_origins[ii], page_size);
         DPRINTF("secure_allocator_create_with_pages: Created MEMP allocator %p with offset %d\n", allocator->table.page_origins[ii], 0);
     }
     DPRINTF("\n");
diff --git a/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_EFM32/TARGET_DEBUG/TARGET_M3/libconfiguration_efm32_m3_p1.a b/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_EFM32/TARGET_DEBUG/TARGET_M3/libconfiguration_efm32_m3_p1.a
index dcc29ad966..81fd1c5655 100644
Binary files a/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_EFM32/TARGET_DEBUG/TARGET_M3/libconfiguration_efm32_m3_p1.a and b/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_EFM32/TARGET_DEBUG/TARGET_M3/libconfiguration_efm32_m3_p1.a differ
diff --git a/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_EFM32/TARGET_DEBUG/TARGET_M4/libconfiguration_efm32_m4_p1.a b/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_EFM32/TARGET_DEBUG/TARGET_M4/libconfiguration_efm32_m4_p1.a
index a4800ce466..f0f62fcbc5 100644
Binary files a/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_EFM32/TARGET_DEBUG/TARGET_M4/libconfiguration_efm32_m4_p1.a and b/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_EFM32/TARGET_DEBUG/TARGET_M4/libconfiguration_efm32_m4_p1.a differ
diff --git a/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_EFM32/TARGET_RELEASE/TARGET_M3/libconfiguration_efm32_m3_p1.a b/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_EFM32/TARGET_RELEASE/TARGET_M3/libconfiguration_efm32_m3_p1.a
index f75adb20b1..1cde51c5bb 100644
Binary files a/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_EFM32/TARGET_RELEASE/TARGET_M3/libconfiguration_efm32_m3_p1.a and b/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_EFM32/TARGET_RELEASE/TARGET_M3/libconfiguration_efm32_m3_p1.a differ
diff --git a/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_EFM32/TARGET_RELEASE/TARGET_M4/libconfiguration_efm32_m4_p1.a b/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_EFM32/TARGET_RELEASE/TARGET_M4/libconfiguration_efm32_m4_p1.a
index 8a65be0520..e2203642d1 100644
Binary files a/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_EFM32/TARGET_RELEASE/TARGET_M4/libconfiguration_efm32_m4_p1.a and b/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_EFM32/TARGET_RELEASE/TARGET_M4/libconfiguration_efm32_m4_p1.a differ
diff --git a/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_MCU_K64F/TARGET_DEBUG/TARGET_M4/libconfiguration_kinetis_m4_0x1fff0000.a b/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_MCU_K64F/TARGET_DEBUG/TARGET_M4/libconfiguration_kinetis_m4_0x1fff0000.a
index eb425e6db2..020d684e6a 100644
Binary files a/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_MCU_K64F/TARGET_DEBUG/TARGET_M4/libconfiguration_kinetis_m4_0x1fff0000.a and b/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_MCU_K64F/TARGET_DEBUG/TARGET_M4/libconfiguration_kinetis_m4_0x1fff0000.a differ
diff --git a/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_MCU_K64F/TARGET_RELEASE/TARGET_M4/libconfiguration_kinetis_m4_0x1fff0000.a b/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_MCU_K64F/TARGET_RELEASE/TARGET_M4/libconfiguration_kinetis_m4_0x1fff0000.a
index 106df75721..d872d526ba 100644
Binary files a/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_MCU_K64F/TARGET_RELEASE/TARGET_M4/libconfiguration_kinetis_m4_0x1fff0000.a and b/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_MCU_K64F/TARGET_RELEASE/TARGET_M4/libconfiguration_kinetis_m4_0x1fff0000.a differ
diff --git a/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_STM32F4/TARGET_DEBUG/TARGET_M4/libconfiguration_stm32_m4_0x10000000_0x0.a b/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_STM32F4/TARGET_DEBUG/TARGET_M4/libconfiguration_stm32_m4_0x10000000_0x0.a
index 43d0c40d74..748df6afb7 100644
Binary files a/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_STM32F4/TARGET_DEBUG/TARGET_M4/libconfiguration_stm32_m4_0x10000000_0x0.a and b/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_STM32F4/TARGET_DEBUG/TARGET_M4/libconfiguration_stm32_m4_0x10000000_0x0.a differ
diff --git a/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_STM32F4/TARGET_RELEASE/TARGET_M4/libconfiguration_stm32_m4_0x10000000_0x0.a b/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_STM32F4/TARGET_RELEASE/TARGET_M4/libconfiguration_stm32_m4_0x10000000_0x0.a
index e04a8e74a8..78818574ec 100644
Binary files a/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_STM32F4/TARGET_RELEASE/TARGET_M4/libconfiguration_stm32_m4_0x10000000_0x0.a and b/features/FEATURE_UVISOR/targets/TARGET_UVISOR_SUPPORTED/TARGET_STM32F4/TARGET_RELEASE/TARGET_M4/libconfiguration_stm32_m4_0x10000000_0x0.a differ
diff --git a/hal/targets/cmsis/TARGET_Freescale/TARGET_MCU_K64F/TOOLCHAIN_GCC_ARM/MK64FN1M0xxx12.ld b/hal/targets/cmsis/TARGET_Freescale/TARGET_MCU_K64F/TOOLCHAIN_GCC_ARM/MK64FN1M0xxx12.ld
index 00abd03f44..4847b76516 100644
--- a/hal/targets/cmsis/TARGET_Freescale/TARGET_MCU_K64F/TOOLCHAIN_GCC_ARM/MK64FN1M0xxx12.ld
+++ b/hal/targets/cmsis/TARGET_Freescale/TARGET_MCU_K64F/TOOLCHAIN_GCC_ARM/MK64FN1M0xxx12.ld
@@ -227,6 +227,16 @@ SECTIONS
     __uvisor_bss_end = .;
   } > m_data
 
+  /* Heap space for the page allocator */
+  .page_heap (NOLOAD) :
+  {
+    . = ALIGN(32);
+    __uvisor_page_start = .;
+    KEEP(*(.keep.uvisor.page_heap))
+    . = ALIGN(32);
+    __uvisor_page_end = .;
+  } > m_data_2
+
   __VECTOR_RAM = DEFINED(__ram_vector_table__) ? __VECTOR_RAM__ : ORIGIN(m_interrupts);
   __RAM_VECTOR_TABLE_SIZE_BYTES = DEFINED(__ram_vector_table__) ? (__interrupts_ram_end__ - __interrupts_ram_start__) : 0x0;
 
@@ -325,21 +335,6 @@ SECTIONS
     __uvisor_heap_end = .;
   } > m_data_2
 
-  .stack :
-  {
-    . = ALIGN(8);
-    . += STACK_SIZE;
-    __StackTop = .;
-  } > m_data_2
-
-  /* Heap space for the page allocator */
-  .page_heap (NOLOAD) :
-  {
-    __uvisor_page_start = .;
-    . = ORIGIN(m_data_2) + LENGTH(m_data_2) - 4;
-    __uvisor_page_end = .;
-  } > m_data_2
-
   m_usb_bdt USB_RAM_START (NOLOAD) :
   {
     *(m_usb_bdt)
@@ -352,6 +347,7 @@ SECTIONS
   }
 
   /* Initializes stack on the end of block */
+  __StackTop = ORIGIN(m_data_2) + LENGTH(m_data_2);
   __StackLimit = __StackTop - STACK_SIZE;
   PROVIDE(__stack = __StackTop);
 
@@ -365,4 +361,3 @@ SECTIONS
   __uvisor_sram_start = ORIGIN(m_data);
   __uvisor_sram_end = ORIGIN(m_data_2) + LENGTH(m_data_2);
 }
-
diff --git a/rtos/rtx/TARGET_CORTEX_M/RTX_CM_lib.h b/rtos/rtx/TARGET_CORTEX_M/RTX_CM_lib.h
index 3c1984a927..2b331a19dd 100644
--- a/rtos/rtx/TARGET_CORTEX_M/RTX_CM_lib.h
+++ b/rtos/rtx/TARGET_CORTEX_M/RTX_CM_lib.h
@@ -421,12 +421,8 @@ osThreadDef_t os_thread_def_main = {(os_pthread)pre_main, osPriorityNormal, 1U,
 #define INITIAL_SP            (0x20003000UL)
 
 #elif defined(TARGET_K64F)
-#if defined(__GNUC__) && !defined(__CC_ARM)     /* GCC */
-extern uint32_t __StackTop[];
-#define INITIAL_SP            (__StackTop)
-#else
 #define INITIAL_SP            (0x20030000UL)
-#endif
+
 #if defined(__CC_ARM) || defined(__GNUC__)
 #define ISR_STACK_SIZE        (0x1000)
 #endif