Re: [PATCH 3/4] kaslr setup_data handling

[Vivek Goyal <vgoyal@redhat.com>]

On Fri, Sep 05, 2014 at 10:32:56AM -0700, Kees Cook wrote:
> On Fri, Sep 05, 2014 at 10:08:16PM +0800, Baoquan He wrote:
> > From: Dave Young <dyoung@redhat.com>
> > 
> > X86 will pass setup_data region while necessary, these regions could be
> > overwitten by kernel due to kaslr.
> > 
> > Thus iterate and add setup regions to mem_avoid[] in this patch.
> > Up to now there isn't a official data to state the maximal entries
> > setup data could use. So just set max mem avoid entries 32, hopefully
> > it will be enough. This can be increased later when people report
> > they are using more setup data entries.
> 
> Ew, yes, this is bad. I hadn't seen setup_data while designing the
> mem_avoid stuff. I don't like the fixed 32 entry size here, so let me
> consider some options. I think the mem_avoid logic can just walk the
> setup_data list itself, since that's what it's for. :)
> 
> Does only kexec use this? I assume other boot loaders must be using this
> too. Is there an easy test case for validating this is fixed?

[CC hpa]

I think this is generic mechanism and any bootloader can make use of it.
May be testing it using kexec on an EFI machine might work as kexec
prepares setup_data entry to pass some information to second kernel.

Thanks
Vivek

> 
> > 
> > Signed-off-by: Dave Young <dyoung@redhat.com>
> > Signed-off-by: Baoquan He <bhe@redhat.com>
> > ---
> >  arch/x86/boot/compressed/aslr.c | 29 +++++++++++++++++++++++++++--
> >  1 file changed, 27 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c
> > index 975b07b..7e92fc8 100644
> > --- a/arch/x86/boot/compressed/aslr.c
> > +++ b/arch/x86/boot/compressed/aslr.c
> > @@ -110,8 +110,9 @@ struct mem_vector {
> >  	unsigned long size;
> >  };
> >  
> > -#define MEM_AVOID_MAX 5
> > +#define MEM_AVOID_MAX 32
> >  static struct mem_vector mem_avoid[MEM_AVOID_MAX];
> > +static int mem_avoid_nr;
> >  
> >  static bool mem_contains(struct mem_vector *region, struct mem_vector *item)
> >  {
> > @@ -135,6 +136,27 @@ static bool mem_overlaps(struct mem_vector *one, struct mem_vector *two)
> >  	return true;
> >  }
> >  
> > +static void mem_avoid_setup_data(void)
> > +{
> > +	struct setup_data *data;
> > +	u64 pa_data;
> > +
> > +	pa_data = real_mode->hdr.setup_data;
> > +	while (pa_data) {
> > +		if (mem_avoid_nr >= MEM_AVOID_MAX) {
> > +			debug_putstr("KASLR: too many setup_data ranges.\n");
> > +			return;
> > +		}
> > +		data = (struct setup_data *)pa_data;
> > +		if (pa_data < CONFIG_RANDOMIZE_BASE_MAX_OFFSET) {
> > +			mem_avoid[mem_avoid_nr].start = pa_data;
> > +			mem_avoid[mem_avoid_nr].size = sizeof(*data) + data->len;
> > +			mem_avoid_nr++;
> > +		}
> > +		pa_data = data->next;
> > +	}
> > +}
> > +
> >  static void mem_avoid_init(unsigned long input, unsigned long input_size,
> >  			   unsigned long output, unsigned long output_size)
> >  {
> > @@ -177,6 +199,9 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
> >  	/* Avoid stack memory. */
> >  	mem_avoid[4].start = (unsigned long)free_mem_end_ptr;
> >  	mem_avoid[4].size = BOOT_STACK_SIZE;
> > +	mem_avoid_nr = 5;
> > +
> > +	mem_avoid_setup_data();
> >  }
> >  
> >  /* Does this memory vector overlap a known avoided area? */
> > @@ -184,7 +209,7 @@ static bool mem_avoid_overlap(struct mem_vector *img)
> >  {
> >  	int i;
> >  
> > -	for (i = 0; i < MEM_AVOID_MAX; i++) {
> > +	for (i = 0; i < mem_avoid_nr; i++) {
> >  		if (mem_overlaps(img, &mem_avoid[i]))
> >  			return true;
> >  	}
> > -- 
> > 1.8.5.3
> 
> Here's an alternative... can you test it?
> 
> ---
> Subject: x86, kaslr: avoid setup_data when choosing kernel location
> 
> The KASLR location-choosing logic needs to avoid the setup_data list
> areas as well.
> 
> Signed-off-by: Kees Cook <keescook@chromium.org>
> Cc: stable@vger.kernel.org
> 
> diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c
> index fc6091abedb7..7c75c22d9bc3 100644
> --- a/arch/x86/boot/compressed/aslr.c
> +++ b/arch/x86/boot/compressed/aslr.c
> @@ -112,6 +112,7 @@ struct mem_vector {
>  
>  #define MEM_AVOID_MAX 5
>  static struct mem_vector mem_avoid[MEM_AVOID_MAX];
> +static struct setup_data *setup_data_avoid;
>  
>  static bool mem_contains(struct mem_vector *region, struct mem_vector *item)
>  {
> @@ -177,17 +178,30 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
>  	/* Avoid stack memory. */
>  	mem_avoid[4].start = (unsigned long)free_mem_end_ptr;
>  	mem_avoid[4].size = BOOT_STACK_SIZE;
> +
> +	/* Locate the setup_data list, if it exists. */
> +	setup_data_avoid = (struct setup_data *)real_mode->hdr.setup_data;
>  }
>  
>  /* Does this memory vector overlap a known avoided area? */
>  static bool mem_avoid_overlap(struct mem_vector *img)
>  {
>  	int i;
> +	struct setup_data *ptr;
>  
>  	for (i = 0; i < MEM_AVOID_MAX; i++) {
>  		if (mem_overlaps(img, &mem_avoid[i]))
>  			return true;
>  	}
> +	for (ptr = setup_data_avoid; ptr; ptr = ptr->next) {
> +		struct mem_vector avoid;
> +
> +		avoid.start = (u64)ptr;
> +		avoid.size = sizeof(*ptr) + ptr->len;
> +
> +		if (mem_overlaps(img, &avoid))
> +			return true;
> +	}
>  
>  	return false;
>  }
> 
> -- 
> Kees Cook
> Chrome OS Security