[PATCH v3 2/2] arm64/acpi: disallow writeable AML opregion mapping for EFI code regions

Ard Biesheuvel ardb at kernel.org
Fri Jun 26 11:58:32 EDT 2020

Given that the contents of EFI runtime code and data regions are
provided by the firmware, as well as the DSDT, it is not unimaginable
that AML code exists today that accesses EFI runtime code regions using
a SystemMemory OpRegion. There is nothing fundamentally wrong with that,
but since we take great care to ensure that executable code is never
mapped writeable and executable at the same time, we should not permit
AML to create writable mapping.

Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
 arch/arm64/kernel/acpi.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
index 01b861e225b0..455966401102 100644
--- a/arch/arm64/kernel/acpi.c
+++ b/arch/arm64/kernel/acpi.c
@@ -301,6 +301,15 @@ void __iomem *acpi_os_ioremap(acpi_physical_address phys, acpi_size size)
 			pr_warn(FW_BUG "requested region covers kernel memory @ %pa\n", &phys);
 			return NULL;
+			/*
+			 * This would be unusual, but not problematic per se,
+			 * as long as we take care not to create a writable
+			 * mapping for executable code.
+			 */
+			prot = PAGE_KERNEL_RO;
+			break;
 			 * ACPI reclaim memory is used to pass firmware tables

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