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SubjectRe: [PATCH v9 2/2] x86/boot/KASLR: Restrict kernel to be randomized in mirror regions
On 17 August 2017 at 14:04, Baoquan He <bhe@redhat.com> wrote:
> On 08/14/17 at 10:54pm, Baoquan He wrote:
>> Currently KASLR will parse all e820 entries of RAM type and add all
>> candidate position into slots array. Then we will choose one slot
>> randomly as the new position which kernel will be decompressed into
>> and run at.
>>
>> On system with EFI enabled, e820 memory regions are coming from EFI
>> memory regions by combining adjacent regions. While these EFI memory
>> regions have more attributes to mark their different use. Mirror
>> attribute is such kind. The physical memory region whose descriptors
>> in EFI memory map has EFI_MEMORY_MORE_RELIABLE attribute (bit: 16) are
>> mirrored. The address range mirroring feature of kernel arranges such
>> mirror region into normal zone and other region into movable zone. And
>> with mirroring feature enabled, the code and date of kernel can only be
>> located in more reliable mirror region. However, the current KASLR code
>> doesn't check EFI memory entries, and could choose new position in
>> non-mirrored region. This will break the functionality of the address
>> range mirroring feature.
>
> Thanks a lot for helping improving the patch log, Ingo! Will pay more
> attention to the description in words and paragraph partition of log.
>
>>
>> So if EFI is detected, iterate EFI memory map and pick the mirror region
>> to process for adding candidate of randomization slot. If EFI is disabled
>> or no mirror region found, still process e820 memory map.
>>
>> Signed-off-by: Baoquan He <bhe@redhat.com>


Could the x86 people on cc either take these directly, or indicate
whether they are ok with this going in via the EFI tree?

Thanks.

>> ---
>> arch/x86/boot/compressed/kaslr.c | 68 ++++++++++++++++++++++++++++++++++++++--
>> 1 file changed, 66 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
>> index 99c7194f7ea6..7de23bb279ce 100644
>> --- a/arch/x86/boot/compressed/kaslr.c
>> +++ b/arch/x86/boot/compressed/kaslr.c
>> @@ -37,7 +37,9 @@
>> #include <linux/uts.h>
>> #include <linux/utsname.h>
>> #include <linux/ctype.h>
>> +#include <linux/efi.h>
>> #include <generated/utsrelease.h>
>> +#include <asm/efi.h>
>>
>> /* Macros used by the included decompressor code below. */
>> #define STATIC
>> @@ -558,6 +560,65 @@ static void process_mem_region(struct mem_vector *entry,
>> }
>> }
>>
>> +#ifdef CONFIG_EFI
>> +/*
>> + * Returns true if mirror region found (and must have been processed
>> + * for slots adding)
>> + */
>> +static bool
>> +process_efi_entries(unsigned long minimum, unsigned long image_size)
>> +{
>> + struct efi_info *e = &boot_params->efi_info;
>> + bool efi_mirror_found = false;
>> + struct mem_vector region;
>> + efi_memory_desc_t *md;
>> + unsigned long pmap;
>> + char *signature;
>> + u32 nr_desc;
>> + int i;
>> +
>> + signature = (char *)&e->efi_loader_signature;
>> + if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&
>> + strncmp(signature, EFI64_LOADER_SIGNATURE, 4))
>> + return false;
>> +
>> +#ifdef CONFIG_X86_32
>> + /* Can't handle data above 4GB at this time */
>> + if (e->efi_memmap_hi) {
>> + warn("EFI memmap is above 4GB, can't be handled now on x86_32. EFI should be disabled.\n");
>> + return false;
>> + }
>> + pmap = e->efi_memmap;
>> +#else
>> + pmap = (e->efi_memmap | ((__u64)e->efi_memmap_hi << 32));
>> +#endif
>> +
>> + nr_desc = e->efi_memmap_size / e->efi_memdesc_size;
>> + for (i = 0; i < nr_desc; i++) {
>> + md = efi_early_memdesc_ptr(pmap, e->efi_memdesc_size, i);
>> + if (md->attribute & EFI_MEMORY_MORE_RELIABLE) {
>> + region.start = md->phys_addr;
>> + region.size = md->num_pages << EFI_PAGE_SHIFT;
>> + process_mem_region(&region, minimum, image_size);
>> + efi_mirror_found = true;
>> +
>> + if (slot_area_index == MAX_SLOT_AREA) {
>> + debug_putstr("Aborted EFI scan (slot_areas full)!\n");
>> + break;
>> + }
>> + }
>> + }
>> +
>> + return efi_mirror_found;
>> +}
>> +#else
>> +static inline bool
>> +process_efi_entries(unsigned long minimum, unsigned long image_size)
>> +{
>> + return false;
>> +}
>> +#endif
>> +
>> static void process_e820_entries(unsigned long minimum,
>> unsigned long image_size)
>> {
>> @@ -586,13 +647,16 @@ static unsigned long find_random_phys_addr(unsigned long minimum,
>> {
>> /* Check if we had too many memmaps. */
>> if (memmap_too_large) {
>> - debug_putstr("Aborted e820 scan (more than 4 memmap= args)!\n");
>> + debug_putstr("Aborted memory entries scan (more than 4 memmap= args)!\n");
>> return 0;
>> }
>>
>> /* Make sure minimum is aligned. */
>> minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
>>
>> + if (process_efi_entries(minimum, image_size))
>> + return slots_fetch_random();
>> +
>> process_e820_entries(minimum, image_size);
>> return slots_fetch_random();
>> }
>> @@ -652,7 +716,7 @@ void choose_random_location(unsigned long input,
>> */
>> min_addr = min(*output, 512UL << 20);
>>
>> - /* Walk e820 and find a random address. */
>> + /* Walk available memory entries to find a random address. */
>> random_addr = find_random_phys_addr(min_addr, output_size);
>> if (!random_addr) {
>> warn("Physical KASLR disabled: no suitable memory region!");
>> --
>> 2.5.5
>>

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