From 18b9c0d641938242d8bcdba3c14a8f2beec2a97e Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel <ard.biesheuvel@linaro.org> Date: Mon, 18 Apr 2016 17:09:46 +0200 Subject: [PATCH] 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> --- arch/arm64/kernel/head.S | 9 +++++---- arch/arm64/kernel/image.h | 2 -- 2 files changed, 5 insertions(+), 6 deletions(-) diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index dae9cabaadf56..c5e5edca6897b 100644 --- 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 4fd72da646a3e..86d444f9c2c12 100644 --- 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; -- GitLab