Re: [PATCH 3/4] kaslr setup_data handling

H. Peter Anvin
2014-09-09T19:49:32Z

setup_data is used by a variety of bootloaders. The first user was large memory machines with more than 128 memory areas.

On September 9, 2014 12:45:00 PM PDT, Vivek Goyal <vgoyal@redhat.com> wrote:
>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

--
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