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x86, kaslr: Raise the maximum virtual address to -1 GiB on x86_64

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On 64-bit, this raises the maximum location to -1 GiB (from -1.5 GiB),
the upper limit currently, since the kernel fixmap page mappings need
to be moved to use the other 1 GiB (which would be the theoretical
limit when building with -mcmodel=kernel).

Signed-off-by: Kees Cook <keescook@chromium.org>
Link: http://lkml.kernel.org/r/1381450698-28710-7-git-send-email-keescook@chromium.org
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Kees Cook 2013-10-10 17:18:18 -07:00 committed by H. Peter Anvin
parent f32360ef66
commit 6145cfe394
4 changed files with 29 additions and 7 deletions
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16
arch/x86/Kconfig
View File

@ -1746,13 +1746,23 @@ config RANDOMIZE_BASE
config RANDOMIZE_BASE_MAX_OFFSET
hex "Maximum ASLR offset allowed"
depends on RANDOMIZE_BASE
default "0x10000000"
range 0x0 0x10000000
range 0x0 0x20000000 if X86_32
default "0x20000000" if X86_32
range 0x0 0x40000000 if X86_64
default "0x40000000" if X86_64
---help---
Determines the maximal offset in bytes that will be applied to the
kernel when Address Space Layout Randomization (ASLR) is active.
Must be less than or equal to the actual physical memory on the
system. This must be a power of two.
system. This must be a multiple of CONFIG_PHYSICAL_ALIGN.
On 32-bit this is limited to 512MiB.
On 64-bit this is limited by how the kernel fixmap page table is
positioned, so this cannot be larger that 1GiB currently. Normally
there is a 512MiB to 1.5GiB split between kernel and modules. When
this is raised above the 512MiB default, the modules area will
shrink to compensate, up to the current maximum 1GiB to 1GiB split.
# Relocation on x86 needs some additional build support
config X86_NEED_RELOCS

15
arch/x86/include/asm/page_64_types.h
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@ -39,9 +39,18 @@
#define __VIRTUAL_MASK_SHIFT 47
/*
* Kernel image size is limited to 512 MB (see level2_kernel_pgt in
* arch/x86/kernel/head_64.S), and it is mapped here:
* Kernel image size is limited to 1GiB due to the fixmap living in the
* next 1GiB (see level2_kernel_pgt in arch/x86/kernel/head_64.S). Use
* 512MiB by default, leaving 1.5GiB for modules once the page tables
* are fully set up. If kernel ASLR is configured, it can extend the
* kernel page table mapping, reducing the size of the modules area.
*/
#define KERNEL_IMAGE_SIZE (512 * 1024 * 1024)
#define KERNEL_IMAGE_SIZE_DEFAULT (512 * 1024 * 1024)
#if defined(CONFIG_RANDOMIZE_BASE) && \
CONFIG_RANDOMIZE_BASE_MAX_OFFSET > KERNEL_IMAGE_SIZE_DEFAULT
#define KERNEL_IMAGE_SIZE CONFIG_RANDOMIZE_BASE_MAX_OFFSET
#else
#define KERNEL_IMAGE_SIZE KERNEL_IMAGE_SIZE_DEFAULT
#endif
#endif /* _ASM_X86_PAGE_64_DEFS_H */

2
arch/x86/include/asm/pgtable_64_types.h
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@ -58,7 +58,7 @@ typedef struct { pteval_t pte; } pte_t;
#define VMALLOC_START _AC(0xffffc90000000000, UL)
#define VMALLOC_END _AC(0xffffe8ffffffffff, UL)
#define VMEMMAP_START _AC(0xffffea0000000000, UL)
#define MODULES_VADDR _AC(0xffffffffa0000000, UL)
#define MODULES_VADDR (__START_KERNEL_map + KERNEL_IMAGE_SIZE)
#define MODULES_END _AC(0xffffffffff000000, UL)
#define MODULES_LEN (MODULES_END - MODULES_VADDR)

3
arch/x86/mm/init_32.c
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@ -806,6 +806,9 @@ void __init mem_init(void)
BUILD_BUG_ON(VMALLOC_START >= VMALLOC_END);
#undef high_memory
#undef __FIXADDR_TOP
#ifdef CONFIG_RANDOMIZE_BASE
BUILD_BUG_ON(CONFIG_RANDOMIZE_BASE_MAX_OFFSET > KERNEL_IMAGE_SIZE);
#endif
#ifdef CONFIG_HIGHMEM
BUG_ON(PKMAP_BASE + LAST_PKMAP*PAGE_SIZE > FIXADDR_START);