Re: [PATCH 1/4] kaslr: check user's config too when handle relocations

Vivek Goyal
2014-09-10T13:20:30Z

On Wed, Sep 10, 2014 at 02:10:35PM +0800, Baoquan He wrote:

[..]
> > > diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> > > index 57ab74d..887f404 100644
> > > --- a/arch/x86/boot/compressed/misc.c
> > > +++ b/arch/x86/boot/compressed/misc.c
> > > @@ -230,8 +230,9 @@ static void error(char *x)
> > > asm("hlt");
> > > }
> > >
> > > -#if CONFIG_X86_NEED_RELOCS
> > > -static void handle_relocations(void *output, unsigned long output_len)
> > > +#ifdef CONFIG_X86_NEED_RELOCS
> > > +static void handle_relocations(void *output_orig, void *output,
> > > + unsigned long output_len)
> > > {
> > > int *reloc;
> > > unsigned long delta, map, ptr;
> > > @@ -242,6 +243,9 @@ static void handle_relocations(void *output, unsigned long output_len)
> > > * Calculate the delta between where vmlinux was linked to load
> > > * and where it was actually loaded.
> > > */
> > > + if (output_orig == output)
> > > + return;
> > > +
> >
> > I still think this needs a test for the 32-bit case, since IUIC, it
> > requires relocations unconditionally.
>
> Oops, just understood that 32 bit kernel alwasy need relocations, but
> only focus on x86_64 and kaslr again when I was doing it. You are right,
> this is not correct for 32 bit kernel.
>
> I am thinking if I can add a compiling condition check like below. This
> only works only when x86_64 or when kaslr is compiled in. Otherwise it
> wokrs as before.
>
> #if CONFIG_X86_64
> if (output_orig == output)
> return;
> #endif

Hi Bao,

I think above should work reasonably well. Also put a comment above it.
Something like as follows.

/*
* 32bit always requires relocations to be performed. For x86_64,
* relocations need to be performed only if kaslr has chosen a
* different load address then kernel was originally loaded at.
*
* If we are here, either kaslr is not configured in or kaslr is disabled
* or kaslr has chosen not to change the load location of kernel. Don't
* perform any relocations.
*/

Thanks
Vivek