[PATCH] [v2] arm64: efi: make sure vmlinux load address aligned on 2MB

[Ard Biesheuvel]

On 29 October 2015 at 03:21, Mark Rutland <mark.rutland at arm.com> wrote:
> On Wed, Oct 28, 2015 at 01:12:36PM -0500, Timur Tabi wrote:
>> On 10/28/2015 01:08 PM, Mark Rutland wrote:
>>
>> >arm64: efi: ensure kernel is loaded at correct address
>> >
>> >The kernel image needs to be loaded text_offset_bytes from a 2M-aligned
>> >base, per Documentation/arm64/booting.txt. If loaded at the wrong offset
>> >modulo 2M, __create_page_tables will create incorrect page tables.
>> >
>> >The EFI stub implicitly assumes that dram_base (i.e. the lowest address
>> >with a EFI_MEMORY_WB attribute) is 2M-aligned, and tries to load the
>> >kernel at dram_base + TEXT_OFFSET. If dram_base is not 2M-aligned, the
>> >kernel will be loaded at the wrong offset from 2M.
>>
>> Thanks, I'll use that.  I messed up a couple other things, so I need
>> to send out a v3 anyway.
>>
>> >>-           *image_addr = *reserve_addr = dram_base + TEXT_OFFSET;
>> >>+           *image_addr = *reserve_addr =
>> >>+                   round_up(dram_base, SZ_2M) + TEXT_OFFSET;
>> >
>> >We also need to fix the test for whether we need to relocate the kernel:
>> >(*image_addr != (dram_base + TEXT_OFFSET)).
>> >
>> >When dram_base is not 2M aligned, that is broken, and it's been broken
>> >since it was introduced in commit 3c7f255039a2ad6e ("arm64: efi: add EFI
>> >stub") in v3.16.
>> >
>> >It's a bit hideous to fix the general case, though, it seems.
>>
>> Um, so I should I do something more in my v3 patch, or is this a
>> change for a different patch?
>
> I think there should be a single patch, but please hold off v3 for a day
> or so. I think there a few more edge cases here, and I'm currently
> investigating.
>

Apologies for the drive-by nature of my contributions to this thread.
I am currently travelling.

I think the below should address both issues (and I even tried to
compile it this time)

-----------------8<-----------------
diff --git a/arch/arm64/kernel/efi-stub.c b/arch/arm64/kernel/efi-stub.c
index 816120ece6bc..78dfbd34b6bf 100644
--- a/arch/arm64/kernel/efi-stub.c
+++ b/arch/arm64/kernel/efi-stub.c
@@ -25,10 +25,20 @@
        unsigned long kernel_size, kernel_memsize = 0;
        unsigned long nr_pages;
        void *old_image_addr = (void *)*image_addr;
+       unsigned long preferred_offset;
+
+       /*
+        * The preferred offset of the kernel Image is TEXT_OFFSET bytes beyond
+        * a 2 MB aligned base, which itself may be lower than dram_base, as
+        * long as the resulting offset equals or exceeds it.
+        */
+       preferred_offset = round_down(dram_base, SZ_2M) + TEXT_OFFSET;
+       if (preferred_offset < dram_base)
+               preferred_offset += SZ_2M;

        /* Relocate the image, if required. */
        kernel_size = _edata - _text;
-       if (*image_addr != (dram_base + TEXT_OFFSET)) {
+       if (*image_addr != preferred_offset) {
                kernel_memsize = kernel_size + (_end - _edata);

                /*
@@ -42,7 +52,7 @@
                 * Mustang), we can still place the kernel at the address
                 * 'dram_base + TEXT_OFFSET'.
                 */
-               *image_addr = *reserve_addr = dram_base + TEXT_OFFSET;
+               *image_addr = *reserve_addr = preferred_offset;
                nr_pages = round_up(kernel_memsize, EFI_ALLOC_ALIGN) /
                           EFI_PAGE_SIZE;
                status = efi_call_early(allocate_pages, EFI_ALLOCATE_ADDRESS,