[PATCH 1/2] arm64/efi: base UEFI mapping permissions on region attributes

[Ard Biesheuvel]

Currently, we infer the UEFI memory region mapping permissions
from the memory region type (i.e., runtime services code are
mapped RWX and runtime services data mapped RW-). This appears to
work fine but is not entirely UEFI spec compliant. So instead, use
the designated permission attributes to decide how these regions
should be mapped.

Since UEFIv2.5 introduces a new EFI_MEMORY_RO permission attribute,
and redefines EFI_MEMORY_WP as a cacheability attribute, use only
the former as a read-only attribute. For setting the PXN bit, the
corresponding EFI_MEMORY_XP attribute is used.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---
 arch/arm64/kernel/efi.c | 32 +++++++++++++-------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
index ab21e0d58278..5dcab58d5d30 100644
--- a/arch/arm64/kernel/efi.c
+++ b/arch/arm64/kernel/efi.c
@@ -247,20 +247,30 @@ static bool __init efi_virtmap_init(void)
 		memrange_efi_to_native(&paddr, &npages);
 		size = npages << PAGE_SHIFT;
 
-		pr_info("  EFI remap 0x%016llx => %p\n",
-			md->phys_addr, (void *)md->virt_addr);
-
-		/*
-		 * Only regions of type EFI_RUNTIME_SERVICES_CODE need to be
-		 * executable, everything else can be mapped with the XN bits
-		 * set.
-		 */
 		if (!is_normal_ram(md))
 			prot = __pgprot(PROT_DEVICE_nGnRE);
-		else if (md->type == EFI_RUNTIME_SERVICES_CODE)
-			prot = PAGE_KERNEL_EXEC;
 		else
-			prot = PAGE_KERNEL;
+			prot = PAGE_KERNEL_EXEC;
+
+		/*
+		 * On 64 KB granule kernels, only use strict permissions when
+		 * the region does not share a 64 KB page frame with another
+		 * region at either end.
+		 */
+		if (!IS_ENABLED(CONFIG_ARM64_64K_PAGES) ||
+		    !(md->virt_addr % PAGE_SIZE ||
+		      (md->phys_addr + md->num_pages * EFI_PAGE_SIZE) % PAGE_SIZE)) {
+
+			if (md->attribute & EFI_MEMORY_RO)
+				prot |= __pgprot(PTE_RDONLY);
+			if (md->attribute & EFI_MEMORY_XP)
+				prot |= __pgprot(PTE_PXN);
+		}
+
+		pr_info("  EFI remap 0x%016llx => %p (R%c%c)\n",
+			md->phys_addr, (void *)md->virt_addr,
+			prot & __pgprot(PTE_RDONLY) ? '-' : 'W',
+			prot & __pgprot(PTE_PXN) ? '-' : 'X');
 
 		create_pgd_mapping(&efi_mm, paddr, md->virt_addr, size, prot);
 	}
-- 
1.9.1