On Mon, Apr 27, 2015 at 04:28:07PM +0200, Jiri Kosina wrote:
> 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.
>
> 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.
>
> Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>
> ---
> arch/x86/include/asm/setup.h | 6 ++++++
> arch/x86/kernel/setup.c | 2 +-
> 2 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
> index f69e06b..785ac2f 100644
> --- a/arch/x86/include/asm/setup.h
> +++ b/arch/x86/include/asm/setup.h
> @@ -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.
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index d74ac33..5056d3c 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -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,
> + kaslr_offset(),
> __START_KERNEL,
> __START_KERNEL_map,
> MODULES_VADDR-1);
It looks like kaslr_offset() can also be used by
arch_crash_save_vmcoreinfo() in machine_kexec_64.c.
--
Josh
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