From: Thomas Garnier <thgar...@google.com>

Add vmemmap in the list of randomized memory regions.

The vmemmap region holds a representation of the physical memory (through
a struct page array). An attacker could use this region to disclose the
kernel memory layout (walking the page linked list).

Signed-off-by: Thomas Garnier <thgar...@google.com>
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 arch/x86/include/asm/kaslr.h            |  1 +
 arch/x86/include/asm/pgtable_64_types.h |  4 +++-
 arch/x86/mm/kaslr.c                     | 24 +++++++++++++++++++++++-
 3 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/kaslr.h b/arch/x86/include/asm/kaslr.h
index 2674ee3de748..1052a797d71d 100644
--- a/arch/x86/include/asm/kaslr.h
+++ b/arch/x86/include/asm/kaslr.h
@@ -6,6 +6,7 @@ unsigned long kaslr_get_random_long(const char *purpose);
 #ifdef CONFIG_RANDOMIZE_MEMORY
 extern unsigned long page_offset_base;
 extern unsigned long vmalloc_base;
+extern unsigned long vmemmap_base;
 
 void kernel_randomize_memory(void);
 #else
diff --git a/arch/x86/include/asm/pgtable_64_types.h 
b/arch/x86/include/asm/pgtable_64_types.h
index 6fdef9eef2d5..3a264200c62f 100644
--- a/arch/x86/include/asm/pgtable_64_types.h
+++ b/arch/x86/include/asm/pgtable_64_types.h
@@ -57,11 +57,13 @@ typedef struct { pteval_t pte; } pte_t;
 #define MAXMEM         _AC(__AC(1, UL) << MAX_PHYSMEM_BITS, UL)
 #define VMALLOC_SIZE_TB        _AC(32, UL)
 #define __VMALLOC_BASE _AC(0xffffc90000000000, UL)
-#define VMEMMAP_START  _AC(0xffffea0000000000, UL)
+#define __VMEMMAP_BASE _AC(0xffffea0000000000, UL)
 #ifdef CONFIG_RANDOMIZE_MEMORY
 #define VMALLOC_START  vmalloc_base
+#define VMEMMAP_START  vmemmap_base
 #else
 #define VMALLOC_START  __VMALLOC_BASE
+#define VMEMMAP_START  __VMEMMAP_BASE
 #endif /* CONFIG_RANDOMIZE_MEMORY */
 #define VMALLOC_END    (VMALLOC_START + _AC((VMALLOC_SIZE_TB << 40) - 1, UL))
 #define MODULES_VADDR    (__START_KERNEL_map + KERNEL_IMAGE_SIZE)
diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index c939cfe1b516..4f91dc273062 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -44,13 +44,22 @@
  * ensure that this order is correct and won't be changed.
  */
 static const unsigned long vaddr_start = __PAGE_OFFSET_BASE;
-static const unsigned long vaddr_end = VMEMMAP_START;
+
+#if defined(CONFIG_X86_ESPFIX64)
+static const unsigned long vaddr_end = ESPFIX_BASE_ADDR;
+#elif defined(CONFIG_EFI)
+static const unsigned long vaddr_end = EFI_VA_START;
+#else
+static const unsigned long vaddr_end = __START_KERNEL_map;
+#endif
 
 /* Default values */
 unsigned long page_offset_base = __PAGE_OFFSET_BASE;
 EXPORT_SYMBOL(page_offset_base);
 unsigned long vmalloc_base = __VMALLOC_BASE;
 EXPORT_SYMBOL(vmalloc_base);
+unsigned long vmemmap_base = __VMEMMAP_BASE;
+EXPORT_SYMBOL(vmemmap_base);
 
 /*
  * Memory regions randomized by KASLR (except modules that use a separate logic
@@ -63,6 +72,7 @@ static __initdata struct kaslr_memory_region {
 } kaslr_regions[] = {
        { &page_offset_base, 64/* Maximum */ },
        { &vmalloc_base, VMALLOC_SIZE_TB },
+       { &vmemmap_base, 1 },
 };
 
 /* Get size in bytes used by the memory region */
@@ -89,6 +99,18 @@ void __init kernel_randomize_memory(void)
        struct rnd_state rand_state;
        unsigned long remain_entropy;
 
+       /*
+        * All these BUILD_BUG_ON checks ensures the memory layout is
+        * consistent with the vaddr_start/vaddr_end variables.
+        */
+       BUILD_BUG_ON(vaddr_start >= vaddr_end);
+       BUILD_BUG_ON(config_enabled(CONFIG_X86_ESPFIX64) &&
+                    vaddr_end >= EFI_VA_START);
+       BUILD_BUG_ON((config_enabled(CONFIG_X86_ESPFIX64) ||
+                     config_enabled(CONFIG_EFI)) &&
+                    vaddr_end >= __START_KERNEL_map);
+       BUILD_BUG_ON(vaddr_end > __START_KERNEL_map);
+
        if (!kaslr_memory_enabled())
                return;
 
-- 
2.7.4

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