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: 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>
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 7983ddf..7bf52ee 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -291,7 +291,7 @@
* 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 @@
* 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 @@
/*
* 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 @@
* 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 @@
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