arm64: add PTE_UXN/PTE_WRITE to SWAPPER_*_FLAGS

With PIE enabled, the swapper PTEs would have a Permission Indirection Index
(PIIndex) of 0. A PIIndex of 0 is not currently used by any other PTEs.

To avoid using index 0 specifically for the swapper PTEs, mark them as
PTE_UXN and PTE_WRITE, so that they map to a PAGE_KERNEL_EXEC equivalent.

This also adds PTE_WRITE to KPTI_NG_PTE_FLAGS, which was tested by booting
with kpti=on.

Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/20230606145859.697944-12-joey.gouly@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Author: jgouly

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

@@ -107,14 +107,14 @@
 /*
  * Initial memory map attributes.
  */
-#define SWAPPER_PTE_FLAGS	(PTE_TYPE_PAGE | PTE_AF | PTE_SHARED)
-#define SWAPPER_PMD_FLAGS	(PMD_TYPE_SECT | PMD_SECT_AF | PMD_SECT_S)
+#define SWAPPER_PTE_FLAGS	(PTE_TYPE_PAGE | PTE_AF | PTE_SHARED | PTE_UXN)
+#define SWAPPER_PMD_FLAGS	(PMD_TYPE_SECT | PMD_SECT_AF | PMD_SECT_S | PTE_UXN)
 
 #ifdef CONFIG_ARM64_4K_PAGES
-#define SWAPPER_RW_MMUFLAGS	(PMD_ATTRINDX(MT_NORMAL) | SWAPPER_PMD_FLAGS)
+#define SWAPPER_RW_MMUFLAGS	(PMD_ATTRINDX(MT_NORMAL) | SWAPPER_PMD_FLAGS | PTE_WRITE)
 #define SWAPPER_RX_MMUFLAGS	(SWAPPER_RW_MMUFLAGS | PMD_SECT_RDONLY)
 #else
-#define SWAPPER_RW_MMUFLAGS	(PTE_ATTRINDX(MT_NORMAL) | SWAPPER_PTE_FLAGS)
+#define SWAPPER_RW_MMUFLAGS	(PTE_ATTRINDX(MT_NORMAL) | SWAPPER_PTE_FLAGS | PTE_WRITE)
 #define SWAPPER_RX_MMUFLAGS	(SWAPPER_RW_MMUFLAGS | PTE_RDONLY)
 #endif
 

arch/arm64/kernel/head.S

@@ -382,7 +382,7 @@ SYM_FUNC_START_LOCAL(create_idmap)
 	adrp	x0, init_idmap_pg_dir
 	adrp	x3, _text
 	adrp	x6, _end + MAX_FDT_SIZE + SWAPPER_BLOCK_SIZE
-	mov	x7, SWAPPER_RX_MMUFLAGS
+	mov_q	x7, SWAPPER_RX_MMUFLAGS
 
 	map_memory x0, x1, x3, x6, x7, x3, IDMAP_PGD_ORDER, x10, x11, x12, x13, x14, EXTRA_SHIFT
 
@@ -391,7 +391,7 @@ SYM_FUNC_START_LOCAL(create_idmap)
 	adrp	x2, init_pg_dir
 	adrp	x3, init_pg_end
 	bic	x4, x2, #SWAPPER_BLOCK_SIZE - 1
-	mov	x5, SWAPPER_RW_MMUFLAGS
+	mov_q	x5, SWAPPER_RW_MMUFLAGS
 	mov	x6, #SWAPPER_BLOCK_SHIFT
 	bl	remap_region
 
@@ -402,7 +402,7 @@ SYM_FUNC_START_LOCAL(create_idmap)
 	bfi	x22, x21, #0, #SWAPPER_BLOCK_SHIFT		// remapped FDT address
 	add	x3, x2, #MAX_FDT_SIZE + SWAPPER_BLOCK_SIZE
 	bic	x4, x21, #SWAPPER_BLOCK_SIZE - 1
-	mov	x5, SWAPPER_RW_MMUFLAGS
+	mov_q	x5, SWAPPER_RW_MMUFLAGS
 	mov	x6, #SWAPPER_BLOCK_SHIFT
 	bl	remap_region
 
@@ -430,7 +430,7 @@ SYM_FUNC_START_LOCAL(create_kernel_mapping)
 	adrp	x3, _text			// runtime __pa(_text)
 	sub	x6, x6, x3			// _end - _text
 	add	x6, x6, x5			// runtime __va(_end)
-	mov	x7, SWAPPER_RW_MMUFLAGS
+	mov_q	x7, SWAPPER_RW_MMUFLAGS
 
 	map_memory x0, x1, x5, x6, x7, x3, (VA_BITS - PGDIR_SHIFT), x10, x11, x12, x13, x14
 

arch/arm64/mm/proc.S

@@ -199,7 +199,7 @@ SYM_FUNC_END(idmap_cpu_replace_ttbr1)
 
 #ifdef CONFIG_UNMAP_KERNEL_AT_EL0
 
-#define KPTI_NG_PTE_FLAGS	(PTE_ATTRINDX(MT_NORMAL) | SWAPPER_PTE_FLAGS)
+#define KPTI_NG_PTE_FLAGS	(PTE_ATTRINDX(MT_NORMAL) | SWAPPER_PTE_FLAGS | PTE_WRITE)
 
 	.pushsection ".idmap.text", "a"
 
@@ -290,7 +290,7 @@ SYM_TYPED_FUNC_START(idmap_kpti_install_ng_mappings)
 	isb
 
 	mov	temp_pte, x5
-	mov	pte_flags, #KPTI_NG_PTE_FLAGS
+	mov_q	pte_flags, KPTI_NG_PTE_FLAGS
 
 	/* Everybody is enjoying the idmap, so we can rewrite swapper. */
 	/* PGD */