[PATCH v4 5/6] arm64: head: clean the ID map page to the PoC

[Ard Biesheuvel]

If we enter with the MMU and caches enabled, the caller may not have
performed any cache maintenance. So clean the ID mapped page to the PoC,
to ensure that instruction and data accesses with the MMU off see the
correct data.

Note that this means primary_entry() itself needs to be moved into the
ID map as well, as we will return from init_kernel_el() with the MMU and
caches off.

Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
 arch/arm64/kernel/head.S | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 5de2ba3539a8..c8b8ed8477c1 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -70,7 +70,7 @@
 
 	__EFI_PE_HEADER
 
-	__INIT
+	.section ".idmap.text","awx"
 
 	/*
 	 * The following callee saved general purpose registers are used on the
@@ -90,6 +90,17 @@ SYM_CODE_START(primary_entry)
 	bl	record_mmu_state
 	bl	preserve_boot_args
 	bl	create_idmap
+
+	/*
+	 * If we entered with the MMU and caches on, clean the ID mapped part
+	 * of the primary boot code to the PoC so we can safely execute it with
+	 * the MMU off.
+	 */
+	cbz	x19, 0f
+	adrp	x0, __idmap_text_start
+	adr_l	x1, __idmap_text_end
+	bl	dcache_clean_poc
+0:
 	bl	init_kernel_el			// w0=cpu_boot_mode
 	mov	x20, x0
 
@@ -111,6 +122,7 @@ SYM_CODE_START(primary_entry)
 	b	__primary_switch
 SYM_CODE_END(primary_entry)
 
+	__INIT
 SYM_CODE_START_LOCAL(record_mmu_state)
 	mrs	x19, CurrentEL
 	cmp	x19, #CurrentEL_EL2
-- 
2.35.1