[PATCH v5 17/21] arm64: head: populate kernel page tables with MMU and caches on

Ard Biesheuvel
2022-06-24T15:15:23Z

Now that we can access the entire kernel image via the ID map, we can
execute the page table population code with the MMU and caches enabled.
The only thing we need to ensure is that translations via TTBR1 remain
disabled while we are updating the page tables the second time around,
in case KASLR wants them to be randomized.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/arm64/kernel/head.S | 62 +++++---------------
1 file changed, 16 insertions(+), 46 deletions(-)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index d704d0bd8ffc..583cbea865e1 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -85,8 +85,6 @@
* x21 primary_entry() .. start_kernel() FDT pointer passed at boot in x0
* x22 create_idmap() .. start_kernel() ID map VA of the DT blob
* x23 primary_entry() .. start_kernel() physical misalignment/KASLR offset
- * x28 clear_page_tables() callee preserved temp register
- * x19/x20 __primary_switch() callee preserved temp registers
* x24 __primary_switch() .. relocate_kernel() current RELR displacement
* x28 create_idmap() callee preserved temp register
*/
@@ -96,9 +94,7 @@ SYM_CODE_START(primary_entry)
adrp x23, __PHYS_OFFSET
and x23, x23, MIN_KIMG_ALIGN - 1 // KASLR offset, defaults to 0
bl set_cpu_boot_mode_flag
- bl clear_page_tables
bl create_idmap
- bl create_kernel_mapping

/*
* The following calls CPU setup code, see arch/arm64/mm/proc.S for
@@ -128,32 +124,14 @@ SYM_CODE_START_LOCAL(preserve_boot_args)
SYM_CODE_END(preserve_boot_args)

SYM_FUNC_START_LOCAL(clear_page_tables)
- mov x28, lr
-
- /*
- * Invalidate the init page tables to avoid potential dirty cache lines
- * being evicted. Other page tables are allocated in rodata as part of
- * the kernel image, and thus are clean to the PoC per the boot
- * protocol.
- */
- adrp x0, init_pg_dir
- adrp x1, init_pg_end
- bl dcache_inval_poc
-
/*
* Clear the init page tables.
*/
adrp x0, init_pg_dir
adrp x1, init_pg_end
- sub x1, x1, x0
-1: stp xzr, xzr, [x0], #16
- stp xzr, xzr, [x0], #16
- stp xzr, xzr, [x0], #16
- stp xzr, xzr, [x0], #16
- subs x1, x1, #64
- b.ne 1b
-
- ret x28
+ sub x2, x1, x0
+ mov x1, xzr
+ b __pi_memset // tail call
SYM_FUNC_END(clear_page_tables)

/*
@@ -399,16 +377,8 @@ SYM_FUNC_START_LOCAL(create_kernel_mapping)

map_memory x0, x1, x5, x6, x7, x3, (VA_BITS - PGDIR_SHIFT), x10, x11, x12, x13, x14

- /*
- * Since the page tables have been populated with non-cacheable
- * accesses (MMU disabled), invalidate those tables again to
- * remove any speculatively loaded cache lines.
- */
- dmb sy
-
- adrp x0, init_pg_dir
- adrp x1, init_pg_end
- b dcache_inval_poc // tail call
+ dsb ishst // sync with page table walker
+ ret
SYM_FUNC_END(create_kernel_mapping)

/*
@@ -863,14 +833,15 @@ SYM_FUNC_END(__relocate_kernel)
#endif

SYM_FUNC_START_LOCAL(__primary_switch)
-#ifdef CONFIG_RANDOMIZE_BASE
- mov x19, x0 // preserve new SCTLR_EL1 value
- mrs x20, sctlr_el1 // preserve old SCTLR_EL1 value
-#endif
-
- adrp x1, init_pg_dir
+ adrp x1, reserved_pg_dir
adrp x2, init_idmap_pg_dir
bl __enable_mmu
+
+ bl clear_page_tables
+ bl create_kernel_mapping
+
+ adrp x1, init_pg_dir
+ load_ttbr1 x1, x1, x2
#ifdef CONFIG_RELOCATABLE
#ifdef CONFIG_RELR
mov x24, #0 // no RELR displacement yet
@@ -886,9 +857,8 @@ SYM_FUNC_START_LOCAL(__primary_switch)
* to take into account by discarding the current kernel mapping and
* creating a new one.
*/
- pre_disable_mmu_workaround
- msr sctlr_el1, x20 // disable the MMU
- isb
+ adrp x1, reserved_pg_dir // Disable translations via TTBR1
+ load_ttbr1 x1, x1, x2
bl clear_page_tables
bl create_kernel_mapping // Recreate kernel mapping

@@ -896,8 +866,8 @@ SYM_FUNC_START_LOCAL(__primary_switch)
dsb nsh
isb

- set_sctlr_el1 x19 // re-enable the MMU
-
+ adrp x1, init_pg_dir // Re-enable translations via TTBR1
+ load_ttbr1 x1, x1, x2
bl __relocate_kernel
#endif
#endif