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Add the generic plumbing to detect whether or not the runtime code regions were constructed with BTI/IBT landing pads by the firmware, permitting the OS to enable enforcement when mapping these regions into the OS's address space. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Reviewed-by: Kees Cook <keescook@chromium.org>
98 lines
2.5 KiB
C
98 lines
2.5 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Copyright (C) 2020 Western Digital Corporation or its affiliates.
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* Adapted from arch/arm64/kernel/efi.c
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*/
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#include <linux/efi.h>
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#include <linux/init.h>
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#include <asm/efi.h>
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#include <asm/pgtable.h>
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#include <asm/pgtable-bits.h>
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/*
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* Only regions of type EFI_RUNTIME_SERVICES_CODE need to be
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* executable, everything else can be mapped with the XN bits
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* set. Also take the new (optional) RO/XP bits into account.
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*/
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static __init pgprot_t efimem_to_pgprot_map(efi_memory_desc_t *md)
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{
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u64 attr = md->attribute;
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u32 type = md->type;
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if (type == EFI_MEMORY_MAPPED_IO)
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return PAGE_KERNEL;
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/* R-- */
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if ((attr & (EFI_MEMORY_XP | EFI_MEMORY_RO)) ==
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(EFI_MEMORY_XP | EFI_MEMORY_RO))
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return PAGE_KERNEL_READ;
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/* R-X */
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if (attr & EFI_MEMORY_RO)
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return PAGE_KERNEL_READ_EXEC;
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/* RW- */
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if (((attr & (EFI_MEMORY_RP | EFI_MEMORY_WP | EFI_MEMORY_XP)) ==
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EFI_MEMORY_XP) ||
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type != EFI_RUNTIME_SERVICES_CODE)
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return PAGE_KERNEL;
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/* RWX */
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return PAGE_KERNEL_EXEC;
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}
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int __init efi_create_mapping(struct mm_struct *mm, efi_memory_desc_t *md)
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{
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pgprot_t prot = __pgprot(pgprot_val(efimem_to_pgprot_map(md)) &
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~(_PAGE_GLOBAL));
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int i;
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/* RISC-V maps one page at a time */
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for (i = 0; i < md->num_pages; i++)
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create_pgd_mapping(mm->pgd, md->virt_addr + i * PAGE_SIZE,
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md->phys_addr + i * PAGE_SIZE,
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PAGE_SIZE, prot);
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return 0;
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}
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static int __init set_permissions(pte_t *ptep, unsigned long addr, void *data)
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{
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efi_memory_desc_t *md = data;
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pte_t pte = READ_ONCE(*ptep);
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unsigned long val;
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if (md->attribute & EFI_MEMORY_RO) {
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val = pte_val(pte) & ~_PAGE_WRITE;
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val |= _PAGE_READ;
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pte = __pte(val);
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}
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if (md->attribute & EFI_MEMORY_XP) {
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val = pte_val(pte) & ~_PAGE_EXEC;
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pte = __pte(val);
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}
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set_pte(ptep, pte);
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return 0;
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}
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int __init efi_set_mapping_permissions(struct mm_struct *mm,
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efi_memory_desc_t *md,
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bool ignored)
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{
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BUG_ON(md->type != EFI_RUNTIME_SERVICES_CODE &&
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md->type != EFI_RUNTIME_SERVICES_DATA);
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/*
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* Calling apply_to_page_range() is only safe on regions that are
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* guaranteed to be mapped down to pages. Since we are only called
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* for regions that have been mapped using efi_create_mapping() above
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* (and this is checked by the generic Memory Attributes table parsing
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* routines), there is no need to check that again here.
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*/
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return apply_to_page_range(mm, md->virt_addr,
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md->num_pages << EFI_PAGE_SHIFT,
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set_permissions, md);
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}
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