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2b5548b681
Since the address of swapper_pg_dir is fixed for a given kernel image, it is an attractive target for manipulation via an arbitrary write. To mitigate this we'd like to make it read-only by moving it into the rodata section. We require that swapper_pg_dir is at a fixed offset from tramp_pg_dir and reserved_ttbr0, so these will also need to move into rodata. However, swapper_pg_dir is allocated along with some transient page tables used for boot which we do not want to move into rodata. As a step towards this, this patch separates the boot-time page tables into a new init_pg_dir, and reduces swapper_pg_dir to the single page it needs to be. This allows us to retain the relationship between swapper_pg_dir, tramp_pg_dir, and swapper_pg_dir, while cleanly separating these from the boot-time page tables. The init_pg_dir holds all of the pgd/pud/pmd/pte levels needed during boot, and all of these levels will be freed when we switch to the swapper_pg_dir, which is initialized by the existing code in paging_init(). Since we start off on the init_pg_dir, we no longer need to allocate a transient page table in paging_init() in order to ensure that swapper_pg_dir isn't live while we initialize it. There should be no functional change as a result of this patch. Signed-off-by: Jun Yao <yaojun8558363@gmail.com> Reviewed-by: James Morse <james.morse@arm.com> [Mark: place init_pg_dir after BSS, fold mm changes, commit message] Signed-off-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
163 lines
5.7 KiB
C
163 lines
5.7 KiB
C
/*
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* Kernel page table mapping
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*
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* Copyright (C) 2015 ARM Ltd.
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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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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef __ASM_KERNEL_PGTABLE_H
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#define __ASM_KERNEL_PGTABLE_H
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#include <asm/pgtable.h>
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#include <asm/sparsemem.h>
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/*
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* The linear mapping and the start of memory are both 2M aligned (per
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* the arm64 booting.txt requirements). Hence we can use section mapping
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* with 4K (section size = 2M) but not with 16K (section size = 32M) or
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* 64K (section size = 512M).
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*/
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#ifdef CONFIG_ARM64_4K_PAGES
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#define ARM64_SWAPPER_USES_SECTION_MAPS 1
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#else
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#define ARM64_SWAPPER_USES_SECTION_MAPS 0
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#endif
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/*
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* The idmap and swapper page tables need some space reserved in the kernel
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* image. Both require pgd, pud (4 levels only) and pmd tables to (section)
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* map the kernel. With the 64K page configuration, swapper and idmap need to
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* map to pte level. The swapper also maps the FDT (see __create_page_tables
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* for more information). Note that the number of ID map translation levels
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* could be increased on the fly if system RAM is out of reach for the default
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* VA range, so pages required to map highest possible PA are reserved in all
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* cases.
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*/
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#if ARM64_SWAPPER_USES_SECTION_MAPS
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#define SWAPPER_PGTABLE_LEVELS (CONFIG_PGTABLE_LEVELS - 1)
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#define IDMAP_PGTABLE_LEVELS (ARM64_HW_PGTABLE_LEVELS(PHYS_MASK_SHIFT) - 1)
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#else
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#define SWAPPER_PGTABLE_LEVELS (CONFIG_PGTABLE_LEVELS)
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#define IDMAP_PGTABLE_LEVELS (ARM64_HW_PGTABLE_LEVELS(PHYS_MASK_SHIFT))
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#endif
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/*
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* If KASLR is enabled, then an offset K is added to the kernel address
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* space. The bottom 21 bits of this offset are zero to guarantee 2MB
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* alignment for PA and VA.
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*
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* For each pagetable level of the swapper, we know that the shift will
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* be larger than 21 (for the 4KB granule case we use section maps thus
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* the smallest shift is actually 30) thus there is the possibility that
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* KASLR can increase the number of pagetable entries by 1, so we make
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* room for this extra entry.
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*
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* Note KASLR cannot increase the number of required entries for a level
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* by more than one because it increments both the virtual start and end
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* addresses equally (the extra entry comes from the case where the end
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* address is just pushed over a boundary and the start address isn't).
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*/
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#ifdef CONFIG_RANDOMIZE_BASE
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#define EARLY_KASLR (1)
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#else
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#define EARLY_KASLR (0)
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#endif
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#define EARLY_ENTRIES(vstart, vend, shift) (((vend) >> (shift)) \
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- ((vstart) >> (shift)) + 1 + EARLY_KASLR)
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#define EARLY_PGDS(vstart, vend) (EARLY_ENTRIES(vstart, vend, PGDIR_SHIFT))
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#if SWAPPER_PGTABLE_LEVELS > 3
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#define EARLY_PUDS(vstart, vend) (EARLY_ENTRIES(vstart, vend, PUD_SHIFT))
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#else
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#define EARLY_PUDS(vstart, vend) (0)
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#endif
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#if SWAPPER_PGTABLE_LEVELS > 2
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#define EARLY_PMDS(vstart, vend) (EARLY_ENTRIES(vstart, vend, SWAPPER_TABLE_SHIFT))
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#else
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#define EARLY_PMDS(vstart, vend) (0)
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#endif
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#define EARLY_PAGES(vstart, vend) ( 1 /* PGDIR page */ \
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+ EARLY_PGDS((vstart), (vend)) /* each PGDIR needs a next level page table */ \
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+ EARLY_PUDS((vstart), (vend)) /* each PUD needs a next level page table */ \
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+ EARLY_PMDS((vstart), (vend))) /* each PMD needs a next level page table */
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#define INIT_DIR_SIZE (PAGE_SIZE * EARLY_PAGES(KIMAGE_VADDR + TEXT_OFFSET, _end))
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#define IDMAP_DIR_SIZE (IDMAP_PGTABLE_LEVELS * PAGE_SIZE)
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#ifdef CONFIG_ARM64_SW_TTBR0_PAN
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#define RESERVED_TTBR0_SIZE (PAGE_SIZE)
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#else
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#define RESERVED_TTBR0_SIZE (0)
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#endif
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/* Initial memory map size */
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#if ARM64_SWAPPER_USES_SECTION_MAPS
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#define SWAPPER_BLOCK_SHIFT SECTION_SHIFT
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#define SWAPPER_BLOCK_SIZE SECTION_SIZE
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#define SWAPPER_TABLE_SHIFT PUD_SHIFT
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#else
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#define SWAPPER_BLOCK_SHIFT PAGE_SHIFT
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#define SWAPPER_BLOCK_SIZE PAGE_SIZE
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#define SWAPPER_TABLE_SHIFT PMD_SHIFT
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#endif
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/* The size of the initial kernel direct mapping */
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#define SWAPPER_INIT_MAP_SIZE (_AC(1, UL) << SWAPPER_TABLE_SHIFT)
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/*
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* Initial memory map attributes.
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*/
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#define SWAPPER_PTE_FLAGS (PTE_TYPE_PAGE | PTE_AF | PTE_SHARED)
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#define SWAPPER_PMD_FLAGS (PMD_TYPE_SECT | PMD_SECT_AF | PMD_SECT_S)
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#if ARM64_SWAPPER_USES_SECTION_MAPS
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#define SWAPPER_MM_MMUFLAGS (PMD_ATTRINDX(MT_NORMAL) | SWAPPER_PMD_FLAGS)
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#else
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#define SWAPPER_MM_MMUFLAGS (PTE_ATTRINDX(MT_NORMAL) | SWAPPER_PTE_FLAGS)
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#endif
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/*
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* To make optimal use of block mappings when laying out the linear
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* mapping, round down the base of physical memory to a size that can
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* be mapped efficiently, i.e., either PUD_SIZE (4k granule) or PMD_SIZE
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* (64k granule), or a multiple that can be mapped using contiguous bits
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* in the page tables: 32 * PMD_SIZE (16k granule)
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*/
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#if defined(CONFIG_ARM64_4K_PAGES)
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#define ARM64_MEMSTART_SHIFT PUD_SHIFT
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#elif defined(CONFIG_ARM64_16K_PAGES)
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#define ARM64_MEMSTART_SHIFT (PMD_SHIFT + 5)
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#else
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#define ARM64_MEMSTART_SHIFT PMD_SHIFT
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#endif
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/*
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* sparsemem vmemmap imposes an additional requirement on the alignment of
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* memstart_addr, due to the fact that the base of the vmemmap region
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* has a direct correspondence, and needs to appear sufficiently aligned
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* in the virtual address space.
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*/
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#if defined(CONFIG_SPARSEMEM_VMEMMAP) && ARM64_MEMSTART_SHIFT < SECTION_SIZE_BITS
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#define ARM64_MEMSTART_ALIGN (1UL << SECTION_SIZE_BITS)
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#else
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#define ARM64_MEMSTART_ALIGN (1UL << ARM64_MEMSTART_SHIFT)
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#endif
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#endif /* __ASM_KERNEL_PGTABLE_H */
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