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6f26b36711
Currently, our KASLR implementation randomizes the placement of the core kernel at 2 MB granularity. This is based on the arm64 kernel boot protocol, which mandates that the kernel is loaded TEXT_OFFSET bytes above a 2 MB aligned base address. This requirement is a result of the fact that the block size used by the early mapping code may be 2 MB at the most (for a 4 KB granule kernel) But we can do better than that: since a KASLR kernel needs to be relocated in any case, we can tolerate a physical misalignment as long as the virtual misalignment relative to this 2 MB block size is equal in size, and code to deal with this is already in place. Since we align the kernel segments to 64 KB, let's randomize the physical offset at 64 KB granularity as well (unless CONFIG_DEBUG_ALIGN_RODATA is enabled). This way, the page table and TLB footprint is not affected. The higher granularity allows for 5 bits of additional entropy to be used. Reviewed-by: Matt Fleming <matt@codeblueprint.co.uk> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com>
142 lines
4.5 KiB
C
142 lines
4.5 KiB
C
/*
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* Copyright (C) 2013, 2014 Linaro Ltd; <roy.franz@linaro.org>
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*
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* This file implements the EFI boot stub for the arm64 kernel.
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* Adapted from ARM version by Mark Salter <msalter@redhat.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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*/
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#include <linux/efi.h>
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#include <asm/efi.h>
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#include <asm/sections.h>
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#include <asm/sysreg.h>
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#include "efistub.h"
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extern bool __nokaslr;
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efi_status_t check_platform_features(efi_system_table_t *sys_table_arg)
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{
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u64 tg;
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/* UEFI mandates support for 4 KB granularity, no need to check */
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if (IS_ENABLED(CONFIG_ARM64_4K_PAGES))
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return EFI_SUCCESS;
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tg = (read_cpuid(ID_AA64MMFR0_EL1) >> ID_AA64MMFR0_TGRAN_SHIFT) & 0xf;
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if (tg != ID_AA64MMFR0_TGRAN_SUPPORTED) {
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if (IS_ENABLED(CONFIG_ARM64_64K_PAGES))
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pr_efi_err(sys_table_arg, "This 64 KB granular kernel is not supported by your CPU\n");
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else
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pr_efi_err(sys_table_arg, "This 16 KB granular kernel is not supported by your CPU\n");
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return EFI_UNSUPPORTED;
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}
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return EFI_SUCCESS;
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}
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efi_status_t handle_kernel_image(efi_system_table_t *sys_table_arg,
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unsigned long *image_addr,
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unsigned long *image_size,
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unsigned long *reserve_addr,
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unsigned long *reserve_size,
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unsigned long dram_base,
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efi_loaded_image_t *image)
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{
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efi_status_t status;
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unsigned long kernel_size, kernel_memsize = 0;
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void *old_image_addr = (void *)*image_addr;
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unsigned long preferred_offset;
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u64 phys_seed = 0;
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if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
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if (!__nokaslr) {
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status = efi_get_random_bytes(sys_table_arg,
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sizeof(phys_seed),
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(u8 *)&phys_seed);
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if (status == EFI_NOT_FOUND) {
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pr_efi(sys_table_arg, "EFI_RNG_PROTOCOL unavailable, no randomness supplied\n");
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} else if (status != EFI_SUCCESS) {
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pr_efi_err(sys_table_arg, "efi_get_random_bytes() failed\n");
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return status;
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}
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} else {
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pr_efi(sys_table_arg, "KASLR disabled on kernel command line\n");
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}
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}
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/*
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* The preferred offset of the kernel Image is TEXT_OFFSET bytes beyond
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* a 2 MB aligned base, which itself may be lower than dram_base, as
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* long as the resulting offset equals or exceeds it.
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*/
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preferred_offset = round_down(dram_base, MIN_KIMG_ALIGN) + TEXT_OFFSET;
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if (preferred_offset < dram_base)
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preferred_offset += MIN_KIMG_ALIGN;
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kernel_size = _edata - _text;
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kernel_memsize = kernel_size + (_end - _edata);
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if (IS_ENABLED(CONFIG_RANDOMIZE_BASE) && phys_seed != 0) {
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/*
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* If CONFIG_DEBUG_ALIGN_RODATA is not set, produce a
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* displacement in the interval [0, MIN_KIMG_ALIGN) that
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* is a multiple of the minimal segment alignment (SZ_64K)
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*/
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u32 mask = (MIN_KIMG_ALIGN - 1) & ~(SZ_64K - 1);
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u32 offset = !IS_ENABLED(CONFIG_DEBUG_ALIGN_RODATA) ?
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(phys_seed >> 32) & mask : TEXT_OFFSET;
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/*
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* If KASLR is enabled, and we have some randomness available,
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* locate the kernel at a randomized offset in physical memory.
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*/
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*reserve_size = kernel_memsize + offset;
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status = efi_random_alloc(sys_table_arg, *reserve_size,
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MIN_KIMG_ALIGN, reserve_addr,
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(u32)phys_seed);
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*image_addr = *reserve_addr + offset;
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} else {
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/*
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* Else, try a straight allocation at the preferred offset.
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* This will work around the issue where, if dram_base == 0x0,
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* efi_low_alloc() refuses to allocate at 0x0 (to prevent the
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* address of the allocation to be mistaken for a FAIL return
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* value or a NULL pointer). It will also ensure that, on
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* platforms where the [dram_base, dram_base + TEXT_OFFSET)
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* interval is partially occupied by the firmware (like on APM
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* Mustang), we can still place the kernel at the address
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* 'dram_base + TEXT_OFFSET'.
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*/
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if (*image_addr == preferred_offset)
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return EFI_SUCCESS;
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*image_addr = *reserve_addr = preferred_offset;
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*reserve_size = round_up(kernel_memsize, EFI_ALLOC_ALIGN);
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status = efi_call_early(allocate_pages, EFI_ALLOCATE_ADDRESS,
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EFI_LOADER_DATA,
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*reserve_size / EFI_PAGE_SIZE,
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(efi_physical_addr_t *)reserve_addr);
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}
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if (status != EFI_SUCCESS) {
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*reserve_size = kernel_memsize + TEXT_OFFSET;
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status = efi_low_alloc(sys_table_arg, *reserve_size,
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MIN_KIMG_ALIGN, reserve_addr);
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if (status != EFI_SUCCESS) {
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pr_efi_err(sys_table_arg, "Failed to relocate kernel\n");
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*reserve_size = 0;
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return status;
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}
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*image_addr = *reserve_addr + TEXT_OFFSET;
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}
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memcpy((void *)*image_addr, old_image_addr, kernel_size);
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return EFI_SUCCESS;
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}
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