[PATCH] xen/arm: Harden setup_frametable_mappings

[Michal Orzel <michal.orzel@xxxxxxx>]

The amount of supported physical memory depends on the frametable size
and the number of struct page_info entries that can fit into it. Define
a macro PAGE_INFO_SIZE to store the current size of the struct page_info
(i.e. 56B for arm64 and 32B for arm32) and add a sanity check in
setup_frametable_mappings to be notified whenever the size of the
structure changes. Also call a panic if the calculated frametable_size
exceeds the limit defined by FRAMETABLE_SIZE macro.

Update the comments regarding the frametable in asm/config.h and take
the opportunity to remove unused macro FRAMETABLE_VIRT_END on arm32.

Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
---
 xen/arch/arm/include/asm/config.h |  5 ++---
 xen/arch/arm/include/asm/mm.h     | 11 +++++++++++
 xen/arch/arm/mm.c                 |  5 +++++
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/xen/arch/arm/include/asm/config.h 
b/xen/arch/arm/include/asm/config.h
index 16213c8b677f..d8f99776986f 100644
--- a/xen/arch/arm/include/asm/config.h
+++ b/xen/arch/arm/include/asm/config.h
@@ -82,7 +82,7 @@
  * ARM32 layout:
  *   0  -  12M   <COMMON>
  *
- *  32M - 128M   Frametable: 24 bytes per page for 16GB of RAM
+ *  32M - 128M   Frametable: 32 bytes per page for 12GB of RAM
  * 256M -   1G   VMAP: ioremap and early_ioremap use this virtual address
  *                    space
  *
@@ -95,7 +95,7 @@
  *
  *   1G -   2G   VMAP: ioremap and early_ioremap
  *
- *  32G -  64G   Frametable: 24 bytes per page for 5.3TB of RAM
+ *  32G -  64G   Frametable: 56 bytes per page for 2TB of RAM
  *
  * 0x0000008000000000 - 0x00007fffffffffff (127.5TB, L0 slots [1..255])
  *  Unused
@@ -127,7 +127,6 @@
 #define FRAMETABLE_VIRT_START  _AT(vaddr_t,0x02000000)
 #define FRAMETABLE_SIZE        MB(128-32)
 #define FRAMETABLE_NR          (FRAMETABLE_SIZE / sizeof(*frame_table))
-#define FRAMETABLE_VIRT_END    (FRAMETABLE_VIRT_START + FRAMETABLE_SIZE - 1)
 
 #define VMAP_VIRT_START        _AT(vaddr_t,0x10000000)
 #define VMAP_VIRT_SIZE         _AT(vaddr_t, GB(1) - MB(256))
diff --git a/xen/arch/arm/include/asm/mm.h b/xen/arch/arm/include/asm/mm.h
index 68adcac9fa8d..23dec574eb31 100644
--- a/xen/arch/arm/include/asm/mm.h
+++ b/xen/arch/arm/include/asm/mm.h
@@ -26,6 +26,17 @@
  */
 #define PFN_ORDER(_pfn) ((_pfn)->v.free.order)
 
+/*
+ * The size of struct page_info impacts the number of entries that can fit
+ * into the frametable area and thus it affects the amount of physical memory
+ * we claim to support. Define PAGE_INFO_SIZE to be used for sanity checking.
+*/
+#ifdef CONFIG_ARM_64
+#define PAGE_INFO_SIZE 56
+#else
+#define PAGE_INFO_SIZE 32
+#endif
+
 struct page_info
 {
     /* Each frame can be threaded onto a doubly-linked list. */
diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 0fc6f2992dd1..a8c28fa5b768 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -676,6 +676,11 @@ void __init setup_frametable_mappings(paddr_t ps, paddr_t 
pe)
     const unsigned long mapping_size = frametable_size < MB(32) ? MB(2) : 
MB(32);
     int rc;
 
+    BUILD_BUG_ON(sizeof(struct page_info) != PAGE_INFO_SIZE);
+
+    if ( frametable_size > FRAMETABLE_SIZE )
+        panic("RAM size is too big to fit in a frametable area\n");
+
     frametable_base_pdx = mfn_to_pdx(maddr_to_mfn(ps));
     /* Round up to 2M or 32M boundary, as appropriate. */
     frametable_size = ROUNDUP(frametable_size, mapping_size);
-- 
2.25.1