x86/mm/64: Enable KASLR for vmemmap memory region

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 <thgarnie@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-hardening@lists.openwall.com
Link: http://lkml.kernel.org/r/1469635196-122447-1-git-send-email-thgarnie@google.com
[ Minor edits. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 24 insertions, 2 deletions

diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index ec8654f117d8..aec03aa96312 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -40,17 +40,26 @@
  * You need to add an if/def entry if you introduce a new memory region
  * compatible with KASLR. Your entry must be in logical order with memory
  * layout. For example, ESPFIX is before EFI because its virtual address is
- * before. You also need to add a BUILD_BUG_ON in kernel_randomize_memory to
+ * before. You also need to add a BUILD_BUG_ON() in kernel_randomize_memory() to
  * 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;