diff options
Diffstat (limited to 'arch/x86/Kconfig')
| -rw-r--r-- | arch/x86/Kconfig | 59 |
1 files changed, 55 insertions, 4 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 5216e283820d..cd18b8393400 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -1693,16 +1693,67 @@ config RELOCATABLE Note: If CONFIG_RELOCATABLE=y, then the kernel runs from the address it has been loaded at and the compile time physical address - (CONFIG_PHYSICAL_START) is ignored. + (CONFIG_PHYSICAL_START) is used as the minimum location. -# Relocation on x86-32 needs some additional build support +config RANDOMIZE_BASE + bool "Randomize the address of the kernel image" + depends on RELOCATABLE + depends on !HIBERNATION + default n + ---help--- + Randomizes the physical and virtual address at which the + kernel image is decompressed, as a security feature that + deters exploit attempts relying on knowledge of the location + of kernel internals. + + Entropy is generated using the RDRAND instruction if it is + supported. If RDTSC is supported, it is used as well. If + neither RDRAND nor RDTSC are supported, then randomness is + read from the i8254 timer. + + The kernel will be offset by up to RANDOMIZE_BASE_MAX_OFFSET, + and aligned according to PHYSICAL_ALIGN. Since the kernel is + built using 2GiB addressing, and PHYSICAL_ALGIN must be at a + minimum of 2MiB, only 10 bits of entropy is theoretically + possible. At best, due to page table layouts, 64-bit can use + 9 bits of entropy and 32-bit uses 8 bits. + + If unsure, say N. + +config RANDOMIZE_BASE_MAX_OFFSET + hex "Maximum kASLR offset allowed" if EXPERT + depends on RANDOMIZE_BASE + range 0x0 0x20000000 if X86_32 + default "0x20000000" if X86_32 + range 0x0 0x40000000 if X86_64 + default "0x40000000" if X86_64 + ---help--- + The lesser of RANDOMIZE_BASE_MAX_OFFSET and available physical + memory is used to determine the maximal offset in bytes that will + be applied to the kernel when kernel Address Space Layout + Randomization (kASLR) is active. This must be a multiple of + PHYSICAL_ALIGN. + + On 32-bit this is limited to 512MiB by page table layouts. The + default is 512MiB. + + On 64-bit this is limited by how the kernel fixmap page table is + positioned, so this cannot be larger than 1GiB currently. Without + RANDOMIZE_BASE, there is a 512MiB to 1.5GiB split between kernel + and modules. When RANDOMIZE_BASE_MAX_OFFSET is above 512MiB, the + modules area will shrink to compensate, up to the current maximum + 1GiB to 1GiB split. The default is 1GiB. + + If unsure, leave at the default value. + +# Relocation on x86 needs some additional build support config X86_NEED_RELOCS def_bool y - depends on X86_32 && RELOCATABLE + depends on RANDOMIZE_BASE || (X86_32 && RELOCATABLE) config PHYSICAL_ALIGN hex "Alignment value to which kernel should be aligned" - default "0x1000000" + default "0x200000" range 0x2000 0x1000000 if X86_32 range 0x200000 0x1000000 if X86_64 ---help--- |