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Merge branch 'x86-kaslr-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 kernel address space randomization support from Peter Anvin: "This enables kernel address space randomization for x86" * 'x86-kaslr-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86, kaslr: Clarify RANDOMIZE_BASE_MAX_OFFSET x86, kaslr: Remove unused including <linux/version.h> x86, kaslr: Use char array to gain sizeof sanity x86, kaslr: Add a circular multiply for better bit diffusion x86, kaslr: Mix entropy sources together as needed x86/relocs: Add percpu fixup for GNU ld 2.23 x86, boot: Rename get_flags() and check_flags() to *_cpuflags() x86, kaslr: Raise the maximum virtual address to -1 GiB on x86_64 x86, kaslr: Report kernel offset on panic x86, kaslr: Select random position from e820 maps x86, kaslr: Provide randomness functions x86, kaslr: Return location from decompress_kernel x86, boot: Move CPU flags out of cpucheck x86, relocs: Add more per-cpu gold special cases
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‎Documentation/kernel-parameters.txt

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@@ -2017,6 +2017,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
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noapic [SMP,APIC] Tells the kernel to not make use of any
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IOAPICs that may be present in the system.
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nokaslr [X86]
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Disable kernel base offset ASLR (Address Space
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Layout Randomization) if built into the kernel.
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noautogroup Disable scheduler automatic task group creation.
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nobats [PPC] Do not use BATs for mapping kernel lowmem

‎arch/x86/Kconfig

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

‎arch/x86/boot/Makefile

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@@ -20,7 +20,7 @@ targets := vmlinux.bin setup.bin setup.elf bzImage
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targets += fdimage fdimage144 fdimage288 image.iso mtools.conf
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subdir- := compressed
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setup-y += a20.o bioscall.o cmdline.o copy.o cpu.o cpucheck.o
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setup-y += a20.o bioscall.o cmdline.o copy.o cpu.o cpuflags.o cpucheck.o
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setup-y += early_serial_console.o edd.o header.o main.o mca.o memory.o
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setup-y += pm.o pmjump.o printf.o regs.o string.o tty.o video.o
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setup-y += video-mode.o version.o

‎arch/x86/boot/boot.h

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@@ -26,9 +26,8 @@
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#include <asm/boot.h>
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#include <asm/setup.h>
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#include "bitops.h"
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#include <asm/cpufeature.h>
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#include <asm/processor-flags.h>
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#include "ctype.h"
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#include "cpuflags.h"
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/* Useful macros */
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#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
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return __cmdline_find_option_bool(cmd_line_ptr, option);
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}
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/* cpu.c, cpucheck.c */
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struct cpu_features {
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int level; /* Family, or 64 for x86-64 */
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int model;
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u32 flags[NCAPINTS];
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};
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extern struct cpu_features cpu;
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int check_cpu(int *cpu_level_ptr, int *req_level_ptr, u32 **err_flags_ptr);
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int validate_cpu(void);
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‎arch/x86/boot/compressed/Makefile

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@@ -28,7 +28,7 @@ HOST_EXTRACFLAGS += -I$(srctree)/tools/include
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VMLINUX_OBJS = $(obj)/vmlinux.lds $(obj)/head_$(BITS).o $(obj)/misc.o \
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$(obj)/string.o $(obj)/cmdline.o $(obj)/early_serial_console.o \
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$(obj)/piggy.o
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$(obj)/piggy.o $(obj)/cpuflags.o $(obj)/aslr.o
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$(obj)/eboot.o: KBUILD_CFLAGS += -fshort-wchar -mno-red-zone
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