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

[Russell King - ARM Linux]

On Sun, Oct 22, 2017 at 03:14:57PM +0100, Ard Biesheuvel wrote:
> 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>

I guess as this is shared between ARM and ARM64, ARM64 folk should ack
this before I merge it - can I have an ack from that side please?

Thanks.

> ---
>  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
> 

-- 
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