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: <sta...@vger.kernel.org> #4.8+
Signed-off-by: Baoquan He <b...@redhat.com>
Acked-by: Dave Young <dyo...@redhat.com>
Reviewed-by: Bhupesh Sharma <bhsha...@redhat.com>
Acked-by: Thomas Garnier <thgar...@google.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Ingo Molnar <mi...@redhat.com>
Cc: "H. Peter Anvin" <h...@zytor.com>
Cc: x...@kernel.org
Cc: Thomas Garnier <thgar...@google.com>
Cc: Kees Cook <keesc...@chromium.org>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Masahiro Yamada <yamada.masah...@socionext.com>
---
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
