[PATCH v8 10/38] arm64/mm: Allocate PIE slots for EL0 guarded control stack

Mark Brown
2024-02-03T12:30:48Z

Pages used for guarded control stacks need to be described to the hardware
using the Permission Indirection Extension, GCS is not supported without
PIE. In order to support copy on write for guarded stacks we allocate two
values, one for active GCSs and one for GCS pages marked as read only prior
to copy.

Since the actual effect is defined using PIE the specific bit pattern used
does not matter to the hardware but we choose two values which differ only
in PTE_WRITE in order to help share code with non-PIE cases.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
arch/arm64/include/asm/pgtable-prot.h | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
index 483dbfa39c4c..14a33e0bece3 100644
--- a/arch/arm64/include/asm/pgtable-prot.h
+++ b/arch/arm64/include/asm/pgtable-prot.h
@@ -129,15 +129,23 @@ extern bool arm64_use_ng_mappings;
/* 6: PTE_PXN | PTE_WRITE */
/* 7: PAGE_SHARED_EXEC PTE_PXN | PTE_WRITE | PTE_USER */
/* 8: PAGE_KERNEL_ROX PTE_UXN */
-/* 9: PTE_UXN | PTE_USER */
+/* 9: PAGE_GCS_RO PTE_UXN | PTE_USER */
/* a: PAGE_KERNEL_EXEC PTE_UXN | PTE_WRITE */
-/* b: PTE_UXN | PTE_WRITE | PTE_USER */
+/* b: PAGE_GCS PTE_UXN | PTE_WRITE | PTE_USER */
/* c: PAGE_KERNEL_RO PTE_UXN | PTE_PXN */
/* d: PAGE_READONLY PTE_UXN | PTE_PXN | PTE_USER */
/* e: PAGE_KERNEL PTE_UXN | PTE_PXN | PTE_WRITE */
/* f: PAGE_SHARED PTE_UXN | PTE_PXN | PTE_WRITE | PTE_USER */

+#define _PAGE_GCS (_PAGE_DEFAULT | PTE_NG | PTE_UXN | PTE_WRITE | PTE_USER)
+#define _PAGE_GCS_RO (_PAGE_DEFAULT | PTE_NG | PTE_UXN | PTE_USER)
+
+#define PAGE_GCS __pgprot(_PAGE_GCS)
+#define PAGE_GCS_RO __pgprot(_PAGE_GCS_RO)
+
#define PIE_E0 ( \
+ PIRx_ELx_PERM(pte_pi_index(_PAGE_GCS), PIE_GCS) | \
+ PIRx_ELx_PERM(pte_pi_index(_PAGE_GCS_RO), PIE_R) | \
PIRx_ELx_PERM(pte_pi_index(_PAGE_EXECONLY), PIE_X_O) | \
PIRx_ELx_PERM(pte_pi_index(_PAGE_READONLY_EXEC), PIE_RX) | \
PIRx_ELx_PERM(pte_pi_index(_PAGE_SHARED_EXEC), PIE_RWX) | \
@@ -145,6 +153,8 @@ extern bool arm64_use_ng_mappings;
PIRx_ELx_PERM(pte_pi_index(_PAGE_SHARED), PIE_RW))

#define PIE_E1 ( \
+ PIRx_ELx_PERM(pte_pi_index(_PAGE_GCS), PIE_NONE_O) | \
+ PIRx_ELx_PERM(pte_pi_index(_PAGE_GCS_RO), PIE_NONE_O) | \
PIRx_ELx_PERM(pte_pi_index(_PAGE_EXECONLY), PIE_NONE_O) | \
PIRx_ELx_PERM(pte_pi_index(_PAGE_READONLY_EXEC), PIE_R) | \
PIRx_ELx_PERM(pte_pi_index(_PAGE_SHARED_EXEC), PIE_RW) | \

--
2.30.2