[PATCH] efi/libstub: arm: omit sorting of the UEFI memory map

[Ard Biesheuvel]

ARM shares its EFI stub implementation with arm64, which has some
special handling in the virtual remapping code to
a) make sure that we can map everything even if the OS executes
   with 64k page size, and
b) make sure that adjacent regions with the same attributes are not
   reordered or moved apart in memory.

The latter is a workaround for a 'feature' that was shortly recommended
by UEFI spec v2.5, but deprecated shortly after, due to the fact that
it broke many OS installers, including non-Linux ones, and it was never
widely implemented for ARM systems. Before implementing b), the arm64
code simply rounded up all regions to 64 KB granularity, but given that
that results in moving adjacent regions apart, it had to be refined when
b) was implemented.

The adjacency check requires a sort() pass, due to the fact that the
UEFI spec does not mandate any ordering, and the inclusion of the
lib/sort.c code into the ARM EFI stub is causing some trouble with
the decompressor build due to the fact that its EXPORT_SYMBOL() call
triggers the creation of ksymtab/kcrctab sections.

So let's simply do away with the adjacency check for ARM, and simply put
all UEFI runtime regions together if they have the same memory attributes.
This is guaranteed to work, given that ARM only supports 4 KB pages,
and allows us to remove the sort() call entirely.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---
 drivers/firmware/efi/libstub/Makefile   | 6 +++---
 drivers/firmware/efi/libstub/arm-stub.c | 7 +++++--
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index dedf9bde44db..f3e8431565ea 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -33,13 +33,14 @@ lib-y				:= efi-stub-helper.o gop.o secureboot.o
 lib-$(CONFIG_RESET_ATTACK_MITIGATION) += tpm.o
 
 # include the stub's generic dependencies from lib/ when building for ARM/arm64
-arm-deps := fdt_rw.c fdt_ro.c fdt_wip.c fdt.c fdt_empty_tree.c fdt_sw.c sort.c
+arm-deps-y := fdt_rw.c fdt_ro.c fdt_wip.c fdt.c fdt_empty_tree.c fdt_sw.c
+arm-deps-$(CONFIG_ARM64) += sort.c
 
 $(obj)/lib-%.o: $(srctree)/lib/%.c FORCE
 	$(call if_changed_rule,cc_o_c)
 
 lib-$(CONFIG_EFI_ARMSTUB)	+= arm-stub.o fdt.o string.o random.o \
-				   $(patsubst %.c,lib-%.o,$(arm-deps))
+				   $(patsubst %.c,lib-%.o,$(arm-deps-y))
 
 lib-$(CONFIG_ARM)		+= arm32-stub.o
 lib-$(CONFIG_ARM64)		+= arm64-stub.o
@@ -90,5 +91,4 @@ quiet_cmd_stubcopy = STUBCPY $@
 # explicitly by the decompressor linker script.
 #
 STUBCOPY_FLAGS-$(CONFIG_ARM)	+= --rename-section .data=.data.efistub
-STUBCOPY_RM-$(CONFIG_ARM)	+= -R ___ksymtab+sort -R ___kcrctab+sort
 STUBCOPY_RELOC-$(CONFIG_ARM)	:= R_ARM_ABS
diff --git a/drivers/firmware/efi/libstub/arm-stub.c b/drivers/firmware/efi/libstub/arm-stub.c
index 1cb2d1c070c3..3061e4057483 100644
--- a/drivers/firmware/efi/libstub/arm-stub.c
+++ b/drivers/firmware/efi/libstub/arm-stub.c
@@ -349,7 +349,9 @@ void efi_get_virtmap(efi_memory_desc_t *memory_map, unsigned long map_size,
 	 * 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);
+	if (IS_ENABLED(CONFIG_ARM64))
+		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;
@@ -366,7 +368,8 @@ void efi_get_virtmap(efi_memory_desc_t *memory_map, unsigned long map_size,
 		 * a 4k page size kernel to kexec a 64k page size kernel and
 		 * vice versa.
 		 */
-		if (!regions_are_adjacent(prev, in) ||
+		if ((IS_ENABLED(CONFIG_ARM64) &&
+		     !regions_are_adjacent(prev, in)) ||
 		    !regions_have_compatible_memory_type_attrs(prev, in)) {
 
 			paddr = round_down(in->phys_addr, SZ_64K);
-- 
2.11.0