arm64: don't map TEXT_OFFSET bytes below the kernel if we can avoid it

For historical reasons, the kernel Image must be loaded into physical
memory at a 512 KB offset above a 2 MB aligned base address. The region
between the base address and the start of the kernel Image has no
significance to the kernel itself, but it is currently mapped explicitly
into the early kernel VMA range for all translation granules.

In some cases (i.e., 4 KB granule), this is unavoidable, due to the 2 MB
granularity of the early kernel mappings. However, in other cases, e.g.,
when running with larger page sizes, or in the future, with more granular
KASLR, there is no reason to map it explicitly like we do currently.

So update the logic so that the region is mapped only if that happens as
a side effect of rounding the start address of the kernel to swapper block
size, and leave it unmapped otherwise.

Since the symbol kernel_img_size now simply resolves to the memory
footprint of the kernel Image, we can drop its definition from image.h
and opencode its calculation.

Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index dae9cabaadf56ab4a8125ee23ecb78c31f434e8e..c5e5edca6897b7a1d8a0735302f0acc29ee11ad5 100644 (file)
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -393,12 +393,13 @@ __create_page_tables:
         * Map the kernel image (starting with PHYS_OFFSET).
         */
        mov     x0, x26                         // swapper_pg_dir
-       mov_q   x5, KIMAGE_VADDR
+       mov_q   x5, KIMAGE_VADDR + TEXT_OFFSET  // compile time __va(_text)
        add     x5, x5, x23                     // add KASLR displacement
        create_pgd_entry x0, x5, x3, x6
-       ldr     w6, =kernel_img_size
-       add     x6, x6, x5
-       mov     x3, x24                         // phys offset
+       adrp    x6, _end                        // runtime __pa(_end)
+       adrp    x3, _text                       // runtime __pa(_text)
+       sub     x6, x6, x3                      // _end - _text
+       add     x6, x6, x5                      // runtime __va(_end)
        create_block_map x0, x7, x3, x5, x6
 
        /*

diff --git a/arch/arm64/kernel/image.h b/arch/arm64/kernel/image.h
index 4fd72da646a3e3a80e98c1314e82b292bf0bc5ec..86d444f9c2c12ae4b18f4b3038ca95d64e34256a 100644 (file)
--- a/arch/arm64/kernel/image.h
+++ b/arch/arm64/kernel/image.h
@@ -71,8 +71,6 @@
        DEFINE_IMAGE_LE64(_kernel_offset_le, TEXT_OFFSET);      \
        DEFINE_IMAGE_LE64(_kernel_flags_le, __HEAD_FLAGS);
 
-kernel_img_size = _end - (_text - TEXT_OFFSET);
-
 #ifdef CONFIG_EFI
 
 __efistub_stext_offset = stext - _text;