139 lines
4.0 KiB
C
139 lines
4.0 KiB
C
/*
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* This code is used on x86_64 to create page table identity mappings on
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* demand by building up a new set of page tables (or appending to the
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* existing ones), and then switching over to them when ready.
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*
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* Copyright (C) 2015-2016 Yinghai Lu
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* Copyright (C) 2016 Kees Cook
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*/
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/*
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* Since we're dealing with identity mappings, physical and virtual
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* addresses are the same, so override these defines which are ultimately
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* used by the headers in misc.h.
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*/
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#define __pa(x) ((unsigned long)(x))
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#define __va(x) ((void *)((unsigned long)(x)))
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#include "misc.h"
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/* These actually do the work of building the kernel identity maps. */
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#include <asm/init.h>
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#include <asm/pgtable.h>
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/* Use the static base for this part of the boot process */
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#undef __PAGE_OFFSET
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#define __PAGE_OFFSET __PAGE_OFFSET_BASE
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#include "../../mm/ident_map.c"
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/* Used by pgtable.h asm code to force instruction serialization. */
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unsigned long __force_order;
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/* Used to track our page table allocation area. */
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struct alloc_pgt_data {
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unsigned char *pgt_buf;
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unsigned long pgt_buf_size;
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unsigned long pgt_buf_offset;
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};
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/*
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* Allocates space for a page table entry, using struct alloc_pgt_data
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* above. Besides the local callers, this is used as the allocation
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* callback in mapping_info below.
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*/
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static void *alloc_pgt_page(void *context)
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{
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struct alloc_pgt_data *pages = (struct alloc_pgt_data *)context;
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unsigned char *entry;
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/* Validate there is space available for a new page. */
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if (pages->pgt_buf_offset >= pages->pgt_buf_size) {
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debug_putstr("out of pgt_buf in " __FILE__ "!?\n");
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debug_putaddr(pages->pgt_buf_offset);
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debug_putaddr(pages->pgt_buf_size);
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return NULL;
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}
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entry = pages->pgt_buf + pages->pgt_buf_offset;
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pages->pgt_buf_offset += PAGE_SIZE;
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return entry;
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}
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/* Used to track our allocated page tables. */
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static struct alloc_pgt_data pgt_data;
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/* The top level page table entry pointer. */
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static unsigned long level4p;
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/*
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* Mapping information structure passed to kernel_ident_mapping_init().
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* Due to relocation, pointers must be assigned at run time not build time.
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*/
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static struct x86_mapping_info mapping_info = {
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.page_flag = __PAGE_KERNEL_LARGE_EXEC,
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};
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/* Locates and clears a region for a new top level page table. */
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void initialize_identity_maps(void)
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{
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/* Init mapping_info with run-time function/buffer pointers. */
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mapping_info.alloc_pgt_page = alloc_pgt_page;
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mapping_info.context = &pgt_data;
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/*
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* It should be impossible for this not to already be true,
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* but since calling this a second time would rewind the other
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* counters, let's just make sure this is reset too.
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*/
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pgt_data.pgt_buf_offset = 0;
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/*
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* If we came here via startup_32(), cr3 will be _pgtable already
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* and we must append to the existing area instead of entirely
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* overwriting it.
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*/
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level4p = read_cr3();
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if (level4p == (unsigned long)_pgtable) {
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debug_putstr("booted via startup_32()\n");
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pgt_data.pgt_buf = _pgtable + BOOT_INIT_PGT_SIZE;
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pgt_data.pgt_buf_size = BOOT_PGT_SIZE - BOOT_INIT_PGT_SIZE;
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memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
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} else {
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debug_putstr("booted via startup_64()\n");
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pgt_data.pgt_buf = _pgtable;
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pgt_data.pgt_buf_size = BOOT_PGT_SIZE;
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memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
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level4p = (unsigned long)alloc_pgt_page(&pgt_data);
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}
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}
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/*
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* Adds the specified range to what will become the new identity mappings.
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* Once all ranges have been added, the new mapping is activated by calling
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* finalize_identity_maps() below.
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*/
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void add_identity_map(unsigned long start, unsigned long size)
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{
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unsigned long end = start + size;
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/* Align boundary to 2M. */
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start = round_down(start, PMD_SIZE);
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end = round_up(end, PMD_SIZE);
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if (start >= end)
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return;
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/* Build the mapping. */
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kernel_ident_mapping_init(&mapping_info, (pgd_t *)level4p,
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start, end);
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}
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/*
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* This switches the page tables to the new level4 that has been built
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* via calls to add_identity_map() above. If booted via startup_32(),
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* this is effectively a no-op.
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*/
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void finalize_identity_maps(void)
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{
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write_cr3(level4p);
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}
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