[PATCH v1 RESEND 1/2] x86/mm/KASLR: EFI region is mistakenly included into KASLR VA space for randomization

[Baoquan He]

Currently KASLR is enabled on three regions: the direct mapping of physical
memory, vamlloc and vmemmap. However 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.

The EFI region is reserved for EFI runtime services virtual mapping which
should not be included in kaslr ranges. It will be re-used by kexec/kdump
kernel, the mistake may cause failure when jump to kexec/kdump kernel if
vmemmap allocation stomps on the allocated efi mapping region.

In Documentation/x86/x86_64/mm.txt, we can see:
  ffffffef00000000 - fffffffeffffffff (=64 GB) EFI region mapping space
EFI use 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.

Cc: <stable@xxxxxxxxxxxxxxx> #4.8+
Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
Acked-by: Dave Young <dyoung@xxxxxxxxxx>
Reviewed-by: Bhupesh Sharma <bhsharma@xxxxxxxxxx>
Acked-by: Thomas Garnier <thgarnie@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> 
Cc: x86@xxxxxxxxxx
Cc: Thomas Garnier <thgarnie@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
---
 arch/x86/mm/kaslr.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index 887e571..aed2064 100644
--- 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);
-- 
2.5.5