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

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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>
This commit is contained in:
Jun Yao
2018-09-24 15:47:49 +01:00
committed by Catalin Marinas
parent 693d5639b4
commit 2b5548b681
6 changed files with 21 additions and 33 deletions
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10
arch/arm64/kernel/head.S
View File

@@ -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

6
arch/arm64/kernel/vmlinux.lds.S
View File

@@ -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 = .;