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/*
* Copyright (c) 2020 Google Inc. All rights reserved
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files
* (the "Software"), to deal in the Software without restriction,
* including without limitation the rights to use, copy, modify, merge,
* publish, distribute, sublicense, and/or sell copies of the Software,
* and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
#include <arch/defines.h>
#include <arch/mmu.h>
#include <assert.h>
#include <endian.h>
#include <inttypes.h>
#include <kernel/vm.h>
#include <lib/rand/rand.h>
#include <trace.h>
#define LOCAL_TRACE 0
vaddr_t aslr_randomize_kernel_base(vaddr_t kernel_base) {
STATIC_ASSERT(!(KERNEL_ASPACE_BASE & (PAGE_SIZE - 1)));
STATIC_ASSERT(!(KERNEL_ASPACE_SIZE & (PAGE_SIZE - 1)));
struct mmu_initial_mapping* second_mapping = &mmu_initial_mappings[1];
if (second_mapping->size) {
LTRACEF("non-kernel mapping phys:0x%" PRIxPTR " virt:0x%" PRIxPTR
" size:%zu\n",
second_mapping->phys, second_mapping->virt,
second_mapping->size);
return kernel_base;
}
struct mmu_initial_mapping* kernel_mapping = mmu_initial_mappings;
kernel_base -= KERNEL_LOAD_OFFSET;
ASSERT(kernel_mapping->virt == kernel_base);
ASSERT(kernel_mapping->size);
ASSERT(!(kernel_mapping->size & (PAGE_SIZE - 1)));
const size_t aspace_pages = KERNEL_ASPACE_SIZE / PAGE_SIZE;
size_t kernel_pages = kernel_mapping->size / PAGE_SIZE;
/* Include 2 guard pages for the kernel */
kernel_pages += 2;
ASSERT(kernel_pages <= aspace_pages);
size_t pick = rand_get_size(aspace_pages - kernel_pages);
kernel_mapping->virt = KERNEL_ASPACE_BASE + ((1 + pick) * PAGE_SIZE);
return kernel_mapping->virt + KERNEL_LOAD_OFFSET;
}
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