c0d7f9802a
Introduce inline header to avoid circular dependency. This will be used in a subsequent patch. Also take opportunity to do some small noop refactor in vma_pad_pages() and split_pad_vma() for more robust code. Bug: 383389169 Bug: 357901498 Change-Id: Ia5f447758d0d07ed3e1429ca1e35dcc0741cc22a Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
70 lines
2.1 KiB
C
70 lines
2.1 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_PAGE_SIZE_MIGRATION_INLINE_H
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#define _LINUX_PAGE_SIZE_MIGRATION_INLINE_H
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/*
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* Page Size Migration
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*
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* Copyright (c) 2024, Google LLC.
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* Author: Kalesh Singh <kaleshsingh@goole.com>
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*
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* This file contains inline APIs for mitigations to ensure
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* app compatibility during the transition from 4kB to 16kB
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* page size in Android.
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*/
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#include <linux/mm_types.h>
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#include <linux/sizes.h>
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#include <asm/page.h>
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/*
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* vm_flags representation of VMA padding pages.
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*
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* This allows the kernel to identify the portion of an ELF LOAD segment VMA
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* that is padding.
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*
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* 4 high bits of vm_flags [62,59] are used to represent ELF segment padding
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* up to 60kB, which is sufficient for ELFs of both 16kB and 64kB segment
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* alignment (p_align).
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*
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* The representation is illustrated below.
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*
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* 62 61 60 59
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* _________ _________ _________ _________
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* | Bit 3 | Bit 2 | Bit 1 | Bit 0 |
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* | of 4kB | of 4kB | of 4kB | of 4kB |
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* | chunks | chunks | chunks | chunks |
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* |_________|_________|_________|_________|
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*
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* NOTE: Bit 63 is already used by mseal()
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*/
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#define VM_PAD_WIDTH 4
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#define VM_PAD_SHIFT (BITS_PER_LONG - VM_PAD_WIDTH - 1)
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#define VM_TOTAL_PAD_PAGES ((1ULL << VM_PAD_WIDTH) - 1)
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#define VM_PAD_MASK (VM_TOTAL_PAD_PAGES << VM_PAD_SHIFT)
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#define VMA_PAD_START(vma) (vma->vm_end - (vma_pad_pages(vma) << PAGE_SHIFT))
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#if PAGE_SIZE == SZ_4K && defined(CONFIG_64BIT)
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/*
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* Sets the correct padding bits / flags for a VMA split.
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*/
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static inline unsigned long vma_pad_fixup_flags(struct vm_area_struct *vma,
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unsigned long newflags)
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{
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if (newflags & VM_PAD_MASK)
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return (newflags & ~VM_PAD_MASK) | (vma->vm_flags & VM_PAD_MASK);
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else
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return newflags;
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}
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#else /* PAGE_SIZE != SZ_4K || !defined(CONFIG_64BIT) */
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static inline unsigned long vma_pad_fixup_flags(struct vm_area_struct *vma,
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unsigned long newflags)
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{
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return newflags;
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}
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#endif /* PAGE_SIZE == SZ_4K && defined(CONFIG_64BIT) */
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#endif /* _LINUX_PAGE_SIZE_MIGRATION_INLINE_H */
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