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