Re: [PATCH 3/4] kaslr setup_data handling

Vivek Goyal
2014-09-09T19:45:10Z

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