x86/mm/KASLR: Exclude EFI region from KASLR VA space randomization

Baoquan He · Ingo Molnar · commit a46f60d76004 · 2017-03-24T09:04:27.000+01:00
Currently KASLR is enabled on three regions: the direct mapping of physical memory, vamlloc and vmemmap. However the EFI region is also mistakenly included for VA space randomization because of misusing EFI_VA_START macro and assuming EFI_VA_START < EFI_VA_END. (This breaks kexec and possibly other things that rely on stable addresses.) The EFI region is reserved for EFI runtime services virtual mapping which should not be included in KASLR ranges. In Documentation/x86/x86_64/mm.txt, we can see: ffffffef00000000 - fffffffeffffffff (=64 GB) EFI region mapping space EFI uses the space from -4G to -64G thus EFI_VA_START > EFI_VA_END, Here EFI_VA_START = -4G, and EFI_VA_END = -64G. Changing EFI_VA_START to EFI_VA_END in mm/kaslr.c fixes this problem. Signed-off-by: Baoquan He <bhe@redhat.com> Reviewed-by: Bhupesh Sharma <bhsharma@redhat.com> Acked-by: Dave Young <dyoung@redhat.com> Acked-by: Thomas Garnier <thgarnie@google.com> Cc: <stable@vger.kernel.org> #4.8+ Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.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: Kees Cook <keescook@chromium.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Masahiro Yamada <yamada.masahiro@socionext.com> Cc: Matt Fleming <matt@codeblueprint.co.uk> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-efi@vger.kernel.org Link: http://lkml.kernel.org/r/1490331592-31860-1-git-send-email-bhe@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
@@ -48,7 +48,7 @@ static const unsigned long vaddr_start = __PAGE_OFFSET_BASE;
 #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;
+static const unsigned long vaddr_end = EFI_VA_END;
 #else
 static const unsigned long vaddr_end = __START_KERNEL_map;
 #endif
@@ -105,7 +105,7 @@ void __init kernel_randomize_memory(void)
 	 */
 	BUILD_BUG_ON(vaddr_start >= vaddr_end);
 	BUILD_BUG_ON(IS_ENABLED(CONFIG_X86_ESPFIX64) &&
-		     vaddr_end >= EFI_VA_START);
+		     vaddr_end >= EFI_VA_END);
 	BUILD_BUG_ON((IS_ENABLED(CONFIG_X86_ESPFIX64) ||
 		      IS_ENABLED(CONFIG_EFI)) &&
 		     vaddr_end >= __START_KERNEL_map);
