Commit 4545c898 authored by Jiri Kosina's avatar Jiri Kosina
Browse files

x86: introduce kaslr_offset()

Offset that has been chosen for kaslr during kernel decompression can be
easily computed as a difference between _text and __START_KERNEL. We are
already making use of this in dump_kernel_offset() notifier and in

Introduce kaslr_offset() that makes this computation instead of hard-coding
it, so that other kernel code (such as live patching) can make use of it.
Also convert existing users to make use of it.

This patch is equivalent transofrmation without any effects on the resulting

	$ diff -u vmlinux.old.asm
	--- vmlinux.old.asm     2015-04-28 17:55:19.520983368 +0200
	+++     2015-04-28 17:55:24.141206072 +0200
	@@ -1,5 +1,5 @@

	-vmlinux.old:     file format elf64-x86-64     file format elf64-x86-64

	Disassembly of section .text:
Acked-by: default avatarBorislav Petkov <>
Signed-off-by: default avatarJiri Kosina <>
parent 9497d738
......@@ -65,12 +65,18 @@ static inline void x86_ce4100_early_setup(void) { }
* This is set up by the setup-routine at boot-time
extern struct boot_params boot_params;
extern char _text[];
static inline bool kaslr_enabled(void)
return !!(boot_params.hdr.loadflags & KASLR_FLAG);
static inline unsigned long kaslr_offset(void)
return (unsigned long)&_text - __START_KERNEL;
* Do NOT EVER look at the BIOS memory size location.
* It does not work on many machines.
......@@ -25,6 +25,7 @@
#include <asm/io_apic.h>
#include <asm/debugreg.h>
#include <asm/kexec-bzimage64.h>
#include <asm/setup.h>
static struct kexec_file_ops *kexec_file_loaders[] = {
......@@ -334,7 +335,7 @@ void arch_crash_save_vmcoreinfo(void)
(unsigned long)&_text - __START_KERNEL);
/* arch-dependent functionality related to kexec file-based syscall */
......@@ -834,7 +834,7 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
if (kaslr_enabled()) {
pr_emerg("Kernel Offset: 0x%lx from 0x%lx (relocation range: 0x%lx-0x%lx)\n",
(unsigned long)&_text - __START_KERNEL,
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