Commit 2b5548b6 authored by Jun Yao's avatar Jun Yao Committed by Catalin Marinas
Browse files

arm64/mm: Separate boot-time page tables from swapper_pg_dir 



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: default avatarJun Yao <yaojun8558363@gmail.com>
Reviewed-by: default avatarJames Morse <james.morse@arm.com>
[Mark: place init_pg_dir after BSS, fold mm changes, commit message]
Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 693d5639

arch/arm64/include/asm/kernel-pgtable.h

+1 −1
Original line number Diff line number Diff line
@@ -97,7 +97,7 @@ 
			+ EARLY_PGDS((vstart), (vend)) 	/* each PGDIR needs a next level page table */	\

			+ EARLY_PUDS((vstart), (vend))	/* each PUD needs a next level page table */	\

			+ EARLY_PMDS((vstart), (vend)))	/* each PMD needs a next level page table */

#define SWAPPER_DIR_SIZE (PAGE_SIZE * EARLY_PAGES(KIMAGE_VADDR + TEXT_OFFSET, _end))

#define INIT_DIR_SIZE (PAGE_SIZE * EARLY_PAGES(KIMAGE_VADDR + TEXT_OFFSET, _end))

#define IDMAP_DIR_SIZE		(IDMAP_PGTABLE_LEVELS * PAGE_SIZE)



#ifdef CONFIG_ARM64_SW_TTBR0_PAN

arch/arm64/include/asm/mmu.h

+3 −0
Original line number Diff line number Diff line
@@ -95,5 +95,8 @@ extern void create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys, 
extern void *fixmap_remap_fdt(phys_addr_t dt_phys);

extern void mark_linear_text_alias_ro(void);



#define INIT_MM_CONTEXT(name)	\

	.pgd = init_pg_dir,



#endif	/* !__ASSEMBLY__ */

#endif

arch/arm64/include/asm/pgtable.h

+2 −1
Original line number Diff line number Diff line
@@ -718,8 +718,9 @@ static inline pmd_t pmdp_establish(struct vm_area_struct *vma, 
}

#endif



extern pgd_t init_pg_dir[PTRS_PER_PGD];

extern pgd_t init_pg_end[];

extern pgd_t swapper_pg_dir[PTRS_PER_PGD];

extern pgd_t swapper_pg_end[];

extern pgd_t idmap_pg_dir[PTRS_PER_PGD];

extern pgd_t tramp_pg_dir[PTRS_PER_PGD];

arch/arm64/kernel/head.S

+5 −5
Original line number Diff line number Diff line
@@ -291,7 +291,7 @@ __create_page_tables: 
	 * dirty cache lines being evicted.

	 */

	adrp	x0, idmap_pg_dir

	adrp	x1, swapper_pg_end

	adrp	x1, init_pg_end

	sub	x1, x1, x0

	bl	__inval_dcache_area
@@ -299,7 +299,7 @@ __create_page_tables: 
	 * Clear the idmap and swapper page tables.

	 */

	adrp	x0, idmap_pg_dir

	adrp	x1, swapper_pg_end

	adrp	x1, init_pg_end

	sub	x1, x1, x0

1:	stp	xzr, xzr, [x0], #16

	stp	xzr, xzr, [x0], #16
@@ -373,7 +373,7 @@ __create_page_tables: 
	/*

	 * Map the kernel image (starting with PHYS_OFFSET).

	 */

	adrp	x0, swapper_pg_dir

	adrp	x0, init_pg_dir

	mov_q	x5, KIMAGE_VADDR + TEXT_OFFSET	// compile time __va(_text)

	add	x5, x5, x23			// add KASLR displacement

	mov	x4, PTRS_PER_PGD
@@ -390,7 +390,7 @@ __create_page_tables: 
	 * tables again to remove any speculatively loaded cache lines.

	 */

	adrp	x0, idmap_pg_dir

	adrp	x1, swapper_pg_end

	adrp	x1, init_pg_end

	sub	x1, x1, x0

	dmb	sy

	bl	__inval_dcache_area
@@ -824,7 +824,7 @@ __primary_switch: 
	mrs	x20, sctlr_el1			// preserve old SCTLR_EL1 value

#endif



	adrp	x1, swapper_pg_dir

	adrp	x1, init_pg_dir

	bl	__enable_mmu

#ifdef CONFIG_RELOCATABLE

	bl	__relocate_kernel

arch/arm64/kernel/vmlinux.lds.S

+5 −1
Original line number Diff line number Diff line
@@ -229,9 +229,13 @@ SECTIONS 
	. += RESERVED_TTBR0_SIZE;

#endif

	swapper_pg_dir = .;

	. += SWAPPER_DIR_SIZE;

	. += PAGE_SIZE;

	swapper_pg_end = .;



	init_pg_dir = .;

	. += INIT_DIR_SIZE;

	init_pg_end = .;



	__pecoff_data_size = ABSOLUTE(. - __initdata_begin);

	_end = .;

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