[PATCH v2] arm64/efi: don't pad between EFI_MEMORY_RUNTIME regions

[Ard Biesheuvel]

The new Properties Table feature introduced in UEFIv2.5 may split
memory regions that cover PE/COFF memory images into separate code
and data regions. Since these regions only differ in the type (runtime
code vs runtime data) and the permission bits, but not in the memory
type attributes (UC/WC/WT/WB), the spec does not require them to be
aligned to 64 KB.

As the relative offset of PE/COFF .text and .data segments cannot be
changed on the fly, this means that we can no longer pad out those
regions to be mappable using 64 KB pages.
Unfortunately, there is no annotation in the UEFI memory map that
identifies data regions that were split off from a code region, so we
must apply this logic to all adjacent runtime regions whose attributes
only differ in the permission bits.

So instead of rounding each memory region to 64 KB alignment at both
ends, only round down regions that are not directly preceded by another
runtime region with the same type attributes. Since the UEFI spec does
not mandate that the memory map be sorted, this means we also need to
sort it first.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---

As discussed off list, this is the arm64 side of what we should backport
to stable to prevent firmware that adheres to the current version of the
UEFI v2.5 spec with the memprotect feature enabled from blowing up the system
upon the first OS call into the runtime services.

For arm64, we already map things in order, but since the spec does not mandate
a sorted memory map, we need to sort it to be sure. This also allows us to
easily find adjacent regions with < 64 KB granularity, which the current version
of the spec allows if they only differ in permission bits (which the spec says
are 'unused' on AArch64, which could be interpreted as 'allowed but ignored').

Changes since v1:
- Ensure that we don't inadvertently set the XN bit on the preceding region at
  mapping time if we the OS is running with >4 KB pages.
  
 arch/arm64/kernel/efi.c                 |  3 +-
 drivers/firmware/efi/libstub/arm-stub.c | 62 +++++++++++++++-----
 2 files changed, 49 insertions(+), 16 deletions(-)

diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
index e8ca6eaedd02..13671a9cf016 100644
--- a/arch/arm64/kernel/efi.c
+++ b/arch/arm64/kernel/efi.c
@@ -258,7 +258,8 @@ static bool __init efi_virtmap_init(void)
 		 */
 		if (!is_normal_ram(md))
 			prot = __pgprot(PROT_DEVICE_nGnRE);
-		else if (md->type == EFI_RUNTIME_SERVICES_CODE)
+		else if (md->type == EFI_RUNTIME_SERVICES_CODE ||
+			 !PAGE_ALIGNED(md->phys_addr))
 			prot = PAGE_KERNEL_EXEC;
 		else
 			prot = PAGE_KERNEL;
diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c
index e29560e6b40b..cb4e9c4de952 100644
--- a/drivers/firmware/efi/libstub/arm-stub.c
+++ b/drivers/firmware/efi/libstub/arm-stub.c
@@ -13,6 +13,7 @@
  */
 
 #include <linux/efi.h>
+#include <linux/sort.h>
 #include <asm/efi.h>
 
 #include "efistub.h"
@@ -305,6 +306,13 @@ fail:
  */
 #define EFI_RT_VIRTUAL_BASE	0x40000000
 
+static int cmp_mem_desc(const void *a, const void *b)
+{
+	const efi_memory_desc_t *left = a, *right = b;
+
+	return (left->phys_addr > right->phys_addr) ? 1 : -1;
+}
+
 /*
  * efi_get_virtmap() - create a virtual mapping for the EFI memory map
  *
@@ -316,34 +324,58 @@ void efi_get_virtmap(efi_memory_desc_t *memory_map, unsigned long map_size,
 		     unsigned long desc_size, efi_memory_desc_t *runtime_map,
 		     int *count)
 {
+	static const u64 mem_type_mask = EFI_MEMORY_WB | EFI_MEMORY_WT |
+					 EFI_MEMORY_WC | EFI_MEMORY_UC |
+					 EFI_MEMORY_RUNTIME;
+
 	u64 efi_virt_base = EFI_RT_VIRTUAL_BASE;
-	efi_memory_desc_t *out = runtime_map;
+	efi_memory_desc_t *in, *prev = NULL, *out = runtime_map;
 	int l;
 
-	for (l = 0; l < map_size; l += desc_size) {
-		efi_memory_desc_t *in = (void *)memory_map + l;
+	/*
+	 * To work around potential issues with the Properties Table feature
+	 * introduced in UEFI 2.5, which may split PE/COFF executable images
+	 * in memory into several RuntimeServicesCode and RuntimeServicesData
+	 * regions, we need to preserve the relative offsets between adjacent
+	 * EFI_MEMORY_RUNTIME regions with the same memory type attributes.
+	 * The easiest way to find adjacent regions is to sort the memory map
+	 * before traversing it.
+	 */
+	sort(memory_map, map_size / desc_size, desc_size, cmp_mem_desc, NULL);
+
+	for (l = 0; l < map_size; l += desc_size, prev = in) {
 		u64 paddr, size;
 
+		in = (void *)memory_map + l;
 		if (!(in->attribute & EFI_MEMORY_RUNTIME))
 			continue;
 
+		paddr = in->phys_addr;
+		size = in->num_pages * EFI_PAGE_SIZE;
+
 		/*
 		 * Make the mapping compatible with 64k pages: this allows
 		 * a 4k page size kernel to kexec a 64k page size kernel and
 		 * vice versa.
 		 */
-		paddr = round_down(in->phys_addr, SZ_64K);
-		size = round_up(in->num_pages * EFI_PAGE_SIZE +
-				in->phys_addr - paddr, SZ_64K);
-
-		/*
-		 * Avoid wasting memory on PTEs by choosing a virtual base that
-		 * is compatible with section mappings if this region has the
-		 * appropriate size and physical alignment. (Sections are 2 MB
-		 * on 4k granule kernels)
-		 */
-		if (IS_ALIGNED(in->phys_addr, SZ_2M) && size >= SZ_2M)
-			efi_virt_base = round_up(efi_virt_base, SZ_2M);
+		if (!prev ||
+		    ((prev->attribute ^ in->attribute) & mem_type_mask) != 0 ||
+		    paddr != (prev->phys_addr + prev->num_pages * EFI_PAGE_SIZE)) {
+
+			paddr = round_down(in->phys_addr, SZ_64K);
+			size += in->phys_addr - paddr;
+
+			/*
+			 * Avoid wasting memory on PTEs by choosing a virtual
+			 * base that is compatible with section mappings if this
+			 * region has the appropriate size and physical
+			 * alignment. (Sections are 2 MB on 4k granule kernels)
+			 */
+			if (IS_ALIGNED(in->phys_addr, SZ_2M) && size >= SZ_2M)
+				efi_virt_base = round_up(efi_virt_base, SZ_2M);
+			else
+				efi_virt_base = round_up(efi_virt_base, SZ_64K);
+		}
 
 		in->virt_addr = efi_virt_base + in->phys_addr - paddr;
 		efi_virt_base += size;
-- 
1.9.1