Since arm64 does not use a decompressor that supplies an execution environment where it is feasible to some extent to provide a source of randomness, the arm64 KASLR kernel depends on the bootloader to supply some random bits in register x1 upon kernel entry.
On UEFI systems, we can use the EFI_RNG_PROTOCOL, if supplied, to obtain some random bits. At the same time, use it to randomize the offset of the kernel Image in physical memory. Signed-off-by: Ard Biesheuvel <[email protected]> --- arch/arm64/kernel/efi-entry.S | 7 +- drivers/firmware/efi/libstub/arm-stub.c | 1 - drivers/firmware/efi/libstub/arm64-stub.c | 134 +++++++++++++++++--- include/linux/efi.h | 5 +- 4 files changed, 127 insertions(+), 20 deletions(-) diff --git a/arch/arm64/kernel/efi-entry.S b/arch/arm64/kernel/efi-entry.S index f82036e02485..f41073dde7e0 100644 --- a/arch/arm64/kernel/efi-entry.S +++ b/arch/arm64/kernel/efi-entry.S @@ -110,7 +110,7 @@ ENTRY(entry) 2: /* Jump to kernel entry point */ mov x0, x20 - mov x1, xzr + ldr x1, efi_rnd mov x2, xzr mov x3, xzr br x21 @@ -119,6 +119,9 @@ efi_load_fail: mov x0, #EFI_LOAD_ERROR ldp x29, x30, [sp], #32 ret +ENDPROC(entry) + +ENTRY(efi_rnd) + .quad 0, 0 entry_end: -ENDPROC(entry) diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c index 950c87f5d279..f580bcdfae4f 100644 --- a/drivers/firmware/efi/libstub/arm-stub.c +++ b/drivers/firmware/efi/libstub/arm-stub.c @@ -145,7 +145,6 @@ void efi_char16_printk(efi_system_table_t *sys_table_arg, out->output_string(out, str); } - /* * This function handles the architcture specific differences between arm and * arm64 regarding where the kernel image must be loaded and any memory that diff --git a/drivers/firmware/efi/libstub/arm64-stub.c b/drivers/firmware/efi/libstub/arm64-stub.c index 78dfbd34b6bf..4e5c306346b4 100644 --- a/drivers/firmware/efi/libstub/arm64-stub.c +++ b/drivers/firmware/efi/libstub/arm64-stub.c @@ -13,6 +13,68 @@ #include <asm/efi.h> #include <asm/sections.h> +struct efi_rng_protocol_t { + efi_status_t (*get_info)(struct efi_rng_protocol_t *, + unsigned long *, + efi_guid_t *); + efi_status_t (*get_rng)(struct efi_rng_protocol_t *, + efi_guid_t *, + unsigned long, + u8 *out); +}; + +extern struct { + u64 virt_seed; + u64 phys_seed; +} efi_rnd; + +static int efi_get_random_bytes(efi_system_table_t *sys_table) +{ + efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID; + efi_status_t status; + struct efi_rng_protocol_t *rng; + + status = sys_table->boottime->locate_protocol(&rng_proto, NULL, + (void **)&rng); + if (status == EFI_NOT_FOUND) { + pr_efi(sys_table, "EFI_RNG_PROTOCOL unavailable, no randomness supplied\n"); + return EFI_SUCCESS; + } + + if (status != EFI_SUCCESS) + return status; + + return rng->get_rng(rng, NULL, sizeof(efi_rnd), (u8 *)&efi_rnd); +} + +static efi_status_t get_dram_top(efi_system_table_t *sys_table_arg, u64 *top) +{ + unsigned long map_size, desc_size; + efi_memory_desc_t *memory_map; + efi_status_t status; + int l; + + status = efi_get_memory_map(sys_table_arg, &memory_map, &map_size, + &desc_size, NULL, NULL); + if (status != EFI_SUCCESS) + return status; + + for (l = 0; l < map_size; l += desc_size) { + efi_memory_desc_t *md = (void *)memory_map + l; + + if (md->attribute & EFI_MEMORY_WB) { + u64 phys_end = md->phys_addr + + md->num_pages * EFI_PAGE_SIZE; + if (phys_end > *top) + *top = phys_end; + } + } + + efi_call_early(free_pool, memory_map); + + return EFI_SUCCESS; +} + efi_status_t __init handle_kernel_image(efi_system_table_t *sys_table_arg, unsigned long *image_addr, unsigned long *image_size, @@ -27,6 +89,14 @@ efi_status_t __init handle_kernel_image(efi_system_table_t *sys_table_arg, void *old_image_addr = (void *)*image_addr; unsigned long preferred_offset; + if (IS_ENABLED(CONFIG_ARM64_RELOCATABLE_KERNEL)) { + status = efi_get_random_bytes(sys_table_arg); + if (status != EFI_SUCCESS) { + pr_efi_err(sys_table_arg, "efi_get_random_bytes() failed\n"); + return status; + } + } + /* * The preferred offset of the kernel Image is TEXT_OFFSET bytes beyond * a 2 MB aligned base, which itself may be lower than dram_base, as @@ -36,13 +106,42 @@ efi_status_t __init handle_kernel_image(efi_system_table_t *sys_table_arg, if (preferred_offset < dram_base) preferred_offset += SZ_2M; - /* Relocate the image, if required. */ kernel_size = _edata - _text; - if (*image_addr != preferred_offset) { - kernel_memsize = kernel_size + (_end - _edata); + kernel_memsize = kernel_size + (_end - _edata); + + if (IS_ENABLED(CONFIG_ARM64_RELOCATABLE_KERNEL) && efi_rnd.phys_seed) { + /* + * If KASLR is enabled, and we have some randomness available, + * locate the kernel at a randomized offset in physical memory. + */ + u64 dram_top = dram_base; + + status = get_dram_top(sys_table_arg, &dram_top); + if (status != EFI_SUCCESS) { + pr_efi_err(sys_table_arg, "get_dram_size() failed\n"); + return status; + } + + kernel_memsize += SZ_2M; + nr_pages = round_up(kernel_memsize, EFI_ALLOC_ALIGN) / + EFI_PAGE_SIZE; /* - * First, try a straight allocation at the preferred offset. + * Use the random seed to scale the size and add it to the DRAM + * base. Note that this may give suboptimal results on systems + * with discontiguous DRAM regions with large holes between them. + */ + *reserve_addr = dram_base + + ((dram_top - dram_base) >> 16) * (u16)efi_rnd.phys_seed; + + status = efi_call_early(allocate_pages, EFI_ALLOCATE_MAX_ADDRESS, + EFI_LOADER_DATA, nr_pages, + (efi_physical_addr_t *)reserve_addr); + + *image_addr = round_up(*reserve_addr, SZ_2M) + TEXT_OFFSET; + } else { + /* + * Else, try a straight allocation at the preferred offset. * This will work around the issue where, if dram_base == 0x0, * efi_low_alloc() refuses to allocate at 0x0 (to prevent the * address of the allocation to be mistaken for a FAIL return @@ -52,27 +151,30 @@ efi_status_t __init handle_kernel_image(efi_system_table_t *sys_table_arg, * Mustang), we can still place the kernel at the address * 'dram_base + TEXT_OFFSET'. */ + if (*image_addr == preferred_offset) + return EFI_SUCCESS; + *image_addr = *reserve_addr = preferred_offset; nr_pages = round_up(kernel_memsize, EFI_ALLOC_ALIGN) / EFI_PAGE_SIZE; status = efi_call_early(allocate_pages, EFI_ALLOCATE_ADDRESS, EFI_LOADER_DATA, nr_pages, (efi_physical_addr_t *)reserve_addr); + } + + if (status != EFI_SUCCESS) { + kernel_memsize += TEXT_OFFSET; + status = efi_low_alloc(sys_table_arg, kernel_memsize, + SZ_2M, reserve_addr); + if (status != EFI_SUCCESS) { - kernel_memsize += TEXT_OFFSET; - status = efi_low_alloc(sys_table_arg, kernel_memsize, - SZ_2M, reserve_addr); - - if (status != EFI_SUCCESS) { - pr_efi_err(sys_table_arg, "Failed to relocate kernel\n"); - return status; - } - *image_addr = *reserve_addr + TEXT_OFFSET; + pr_efi_err(sys_table_arg, "Failed to relocate kernel\n"); + return status; } - memcpy((void *)*image_addr, old_image_addr, kernel_size); - *reserve_size = kernel_memsize; + *image_addr = *reserve_addr + TEXT_OFFSET; } - + memcpy((void *)*image_addr, old_image_addr, kernel_size); + *reserve_size = kernel_memsize; return EFI_SUCCESS; } diff --git a/include/linux/efi.h b/include/linux/efi.h index 569b5a866bb1..13783fdc9bdd 100644 --- a/include/linux/efi.h +++ b/include/linux/efi.h @@ -299,7 +299,7 @@ typedef struct { void *open_protocol_information; void *protocols_per_handle; void *locate_handle_buffer; - void *locate_protocol; + efi_status_t (*locate_protocol)(efi_guid_t *, void *, void **); void *install_multiple_protocol_interfaces; void *uninstall_multiple_protocol_interfaces; void *calculate_crc32; @@ -599,6 +599,9 @@ void efi_native_runtime_setup(void); #define EFI_PROPERTIES_TABLE_GUID \ EFI_GUID( 0x880aaca3, 0x4adc, 0x4a04, 0x90, 0x79, 0xb7, 0x47, 0x34, 0x08, 0x25, 0xe5 ) +#define EFI_RNG_PROTOCOL_GUID \ + EFI_GUID( 0x3152bca5, 0xeade, 0x433d, 0x86, 0x2e, 0xc0, 0x1c, 0xdc, 0x29, 0x1f, 0x44 ) + typedef struct { efi_guid_t guid; u64 table; -- 2.5.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
