The branch main has been updated by andrew:
URL:
https://cgit.FreeBSD.org/src/commit/?id=ea8dc498aa8ea91ce0364a3f0ccdb740a24dcfb4
commit ea8dc498aa8ea91ce0364a3f0ccdb740a24dcfb4
Author: Andrew Turner <and...@freebsd.org>
AuthorDate: 2025-06-17 10:12:00 +0000
Commit: Andrew Turner <and...@freebsd.org>
CommitDate: 2025-06-17 12:48:22 +0000
arm64: Create an L3 table to limit permissions
When building a 4k page kernel we use 2M blocks to map the kernel
contents. As the .text section may not end on a 2M aligned address
we need to split one block into level 3 pages and pad the end of the
section to an appropriate boundary.
With both these changes we can then mapjust the code as executable.
While here also map it as read-only as none ofthis shouldbe written
to directly.
Reviewed by: alc
Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D45064
---
sys/arm64/arm64/locore.S | 62 +++++++++++++++++++++++++++++++++++++++++-------
sys/conf/ldscript.arm64 | 6 +++++
2 files changed, 60 insertions(+), 8 deletions(-)
diff --git a/sys/arm64/arm64/locore.S b/sys/arm64/arm64/locore.S
index fcc3f948f00c..2f549a527f43 100644
--- a/sys/arm64/arm64/locore.S
+++ b/sys/arm64/arm64/locore.S
@@ -45,6 +45,12 @@
* space, the same as a single level 2 page with 4k pages.
*/
#define L3_PAGE_COUNT 32
+#elif PAGE_SIZE == PAGE_SIZE_4K
+/*
+ * Space for a level 3 table holding the end of the executable memory and
+ * the start of the non-executable data.
+ */
+#define L3_PAGE_COUNT 1
#endif
/*
@@ -600,22 +606,64 @@ common:
/* Get the number of blocks/pages to allocate, rounded down */
lsr x14, x8, #(PTE_SHIFT)
- ldr x25, =etext
+ ldr x26, =etext
+#if PAGE_SIZE != PAGE_SIZE_4K
ldr x8, =((1 << PTE_SHIFT) - 1)
- add x25, x25, x8
+ add x26, x26, x8
+#endif
mov x8, #(KERNBASE)
- sub x25, x25, x8
+ sub x25, x26, x8
lsr x25, x25, #(PTE_SHIFT)
+#if PAGE_SIZE == PAGE_SIZE_4K
+ /* Calculate the number of executable level 3 pages to create */
+ lsr x26, x26, #(L3_SHIFT)
+ bfc x26, #(Ln_ENTRIES_SHIFT), #(64 - Ln_ENTRIES_SHIFT)
+
+ /* Build the L3 table holding the end of the exectuable code */
+ lsl x15, x25, #(PTE_SHIFT)
+ adrp x6, pagetable_l3_ttbr1
+ add x6, x6, :lo12:pagetable_l3_ttbr1
+ ldr x7, =(ATTR_S1_IDX(VM_MEMATTR_WRITE_BACK) | \
+ ATTR_S1_AP(ATTR_S1_AP_RO))
+ ldr x8, =(KERNBASE)
+ add x8, x8, x15
+ add x9, x28, x15
+ mov x10, x26
+ bl build_l3_page_pagetable
+
+ /* Build the remaining level 3 pages */
+ ldr x7, =(ATTR_S1_IDX(VM_MEMATTR_WRITE_BACK) | ATTR_S1_XN)
+ lsl x27, x26, #(L3_SHIFT)
+ add x8, x8, x27
+ add x9, x28, x15
+ add x9, x9, x27
+ ldr x10, =(Ln_ENTRIES)
+ sub x10, x10, x26
+ bl build_l3_page_pagetable
+
+ /* Link the l2 -> l3 table */
+ mov x9, x6
+ adrp x6, pagetable_l2_ttbr1
+ add x6, x6, :lo12:pagetable_l2_ttbr1
+ bl link_l2_pagetable
+#endif
+
/* Create the kernel space PTE table */
adrp x6, LL_PAGE_TABLE
add x6, x6, :lo12:LL_PAGE_TABLE
- mov x7, #(ATTR_S1_IDX(VM_MEMATTR_WRITE_BACK))
+ ldr x7, =(ATTR_S1_IDX(VM_MEMATTR_WRITE_BACK) | \
+ ATTR_S1_AP(ATTR_S1_AP_RO))
mov x8, #(KERNBASE)
mov x9, x28
mov x10, x25
bl BUILD_PTE_FUNC
+#if PAGE_SIZE == PAGE_SIZE_4K
+ /* Skip memory mapped through the L2 table */
+ add x25, x25, #1
+#endif
+
/* Create the kernel space XN PTE table */
lsl x10, x25, #(PTE_SHIFT)
ldr x7, =(ATTR_S1_IDX(VM_MEMATTR_WRITE_BACK) | ATTR_S1_XN)
@@ -837,7 +885,6 @@ LENTRY(build_l2_block_pagetable)
ret
LEND(build_l2_block_pagetable)
-#if PAGE_SIZE != PAGE_SIZE_4K
/*
* Builds an L2 -> L3 table descriptor
*
@@ -881,6 +928,7 @@ LEND(link_l2_pagetable)
* VA start (x8) modulo L3C_SIZE must equal PA start (x9) modulo L3C_SIZE.
*/
LENTRY(build_l3_page_pagetable)
+ cbz x10, 2f
/*
* Build the L3 table entry.
*/
@@ -920,10 +968,10 @@ LENTRY(build_l3_page_pagetable)
add x11, x11, #1
add x9, x9, #1
cbnz x10, 1b
+2:
ret
LEND(build_l3_page_pagetable)
-#endif
LENTRY(start_mmu)
dsb sy
@@ -1054,10 +1102,8 @@ initstack_end:
*/
.globl pagetable_l0_ttbr1
pagetable:
-#if PAGE_SIZE != PAGE_SIZE_4K
pagetable_l3_ttbr1:
.space (PAGE_SIZE * L3_PAGE_COUNT)
-#endif
pagetable_l2_ttbr1:
.space PAGE_SIZE
pagetable_l1_ttbr1:
diff --git a/sys/conf/ldscript.arm64 b/sys/conf/ldscript.arm64
index 0d50eef431cf..ae231c3037e6 100644
--- a/sys/conf/ldscript.arm64
+++ b/sys/conf/ldscript.arm64
@@ -15,6 +15,12 @@ SECTIONS
*(.gnu.warning)
*(.gnu.linkonce.t*)
} =0x9090
+ /*
+ * Align to the the largest page size the kernel could be built for.
+ * If we don't then building page tables in locore.S could fail as it
+ * assumes the .text section is on a different page to later sections.
+ */
+ . = ALIGN(CONSTANT(MAXPAGESIZE));
_etext = .;
PROVIDE (etext = .);
