From: Arvind Sankar nivedita@alum.mit.edu
[ Upstream commit 451286940d95778e83fa7f97006316d995b4c4a8 ]
On 64-bit, the kernel must be placed below MAXMEM (64TiB with 4-level paging or 4PiB with 5-level paging). This is currently not enforced by KASLR, which thus implicitly relies on physical memory being limited to less than 64TiB.
On 32-bit, the limit is KERNEL_IMAGE_SIZE (512MiB). This is enforced by special checks in __process_mem_region().
Initialize mem_limit to the maximum (depending on architecture), instead of ULLONG_MAX, and make sure the command-line arguments can only decrease it. This makes the enforcement explicit on 64-bit, and eliminates the 32-bit specific checks to keep the kernel below 512M.
Check upfront to make sure the minimum address is below the limit before doing any work.
Signed-off-by: Arvind Sankar nivedita@alum.mit.edu Signed-off-by: Ingo Molnar mingo@kernel.org Acked-by: Kees Cook keescook@chromium.org Link: https://lore.kernel.org/r/20200727230801.3468620-5-nivedita@alum.mit.edu Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/boot/compressed/kaslr.c | 41 +++++++++++++++++--------------- 1 file changed, 22 insertions(+), 19 deletions(-)
diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c index dde7cb3724df3..9bd966ef7d19e 100644 --- a/arch/x86/boot/compressed/kaslr.c +++ b/arch/x86/boot/compressed/kaslr.c @@ -87,8 +87,11 @@ static unsigned long get_boot_seed(void) static bool memmap_too_large;
-/* Store memory limit specified by "mem=nn[KMG]" or "memmap=nn[KMG]" */ -static unsigned long long mem_limit = ULLONG_MAX; +/* + * Store memory limit: MAXMEM on 64-bit and KERNEL_IMAGE_SIZE on 32-bit. + * It may be reduced by "mem=nn[KMG]" or "memmap=nn[KMG]" command line options. + */ +static unsigned long long mem_limit;
/* Number of immovable memory regions */ static int num_immovable_mem; @@ -214,7 +217,7 @@ static void mem_avoid_memmap(enum parse_mode mode, char *str)
if (start == 0) { /* Store the specified memory limit if size > 0 */ - if (size > 0) + if (size > 0 && size < mem_limit) mem_limit = size;
continue; @@ -302,7 +305,8 @@ static void handle_mem_options(void) if (mem_size == 0) goto out;
- mem_limit = mem_size; + if (mem_size < mem_limit) + mem_limit = mem_size; } else if (!strcmp(param, "efi_fake_mem")) { mem_avoid_memmap(PARSE_EFI, val); } @@ -314,7 +318,9 @@ static void handle_mem_options(void) }
/* - * In theory, KASLR can put the kernel anywhere in the range of [16M, 64T). + * In theory, KASLR can put the kernel anywhere in the range of [16M, MAXMEM) + * on 64-bit, and [16M, KERNEL_IMAGE_SIZE) on 32-bit. + * * The mem_avoid array is used to store the ranges that need to be avoided * when KASLR searches for an appropriate random address. We must avoid any * regions that are unsafe to overlap with during decompression, and other @@ -614,10 +620,6 @@ static void __process_mem_region(struct mem_vector *entry, unsigned long start_orig, end; struct mem_vector cur_entry;
- /* On 32-bit, ignore entries entirely above our maximum. */ - if (IS_ENABLED(CONFIG_X86_32) && entry->start >= KERNEL_IMAGE_SIZE) - return; - /* Ignore entries entirely below our minimum. */ if (entry->start + entry->size < minimum) return; @@ -650,11 +652,6 @@ static void __process_mem_region(struct mem_vector *entry, /* Reduce size by any delta from the original address. */ region.size -= region.start - start_orig;
- /* On 32-bit, reduce region size to fit within max size. */ - if (IS_ENABLED(CONFIG_X86_32) && - region.start + region.size > KERNEL_IMAGE_SIZE) - region.size = KERNEL_IMAGE_SIZE - region.start; - /* Return if region can't contain decompressed kernel */ if (region.size < image_size) return; @@ -839,15 +836,16 @@ static void process_e820_entries(unsigned long minimum, static unsigned long find_random_phys_addr(unsigned long minimum, unsigned long image_size) { + /* Bail out early if it's impossible to succeed. */ + if (minimum + image_size > mem_limit) + return 0; + /* Check if we had too many memmaps. */ if (memmap_too_large) { 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();
@@ -860,8 +858,6 @@ static unsigned long find_random_virt_addr(unsigned long minimum, { unsigned long slots, random_addr;
- /* Make sure minimum is aligned. */ - minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN); /* Align image_size for easy slot calculations. */ image_size = ALIGN(image_size, CONFIG_PHYSICAL_ALIGN);
@@ -908,6 +904,11 @@ void choose_random_location(unsigned long input, /* Prepare to add new identity pagetables on demand. */ initialize_identity_maps();
+ if (IS_ENABLED(CONFIG_X86_32)) + mem_limit = KERNEL_IMAGE_SIZE; + else + mem_limit = MAXMEM; + /* Record the various known unsafe memory ranges. */ mem_avoid_init(input, input_size, *output);
@@ -917,6 +918,8 @@ void choose_random_location(unsigned long input, * location: */ min_addr = min(*output, 512UL << 20); + /* Make sure minimum is aligned. */ + min_addr = ALIGN(min_addr, CONFIG_PHYSICAL_ALIGN);
/* Walk available memory entries to find a random address. */ random_addr = find_random_phys_addr(min_addr, output_size);