linux-kernel - Re: [PATCH v2 02/13] arm64: introduce KIMAGE_VADDR as the virtual base of the kernel region

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Message-ID: <20160105143634.GD28354@cbox>
Date:	Tue, 5 Jan 2016 15:36:34 +0100
From:	Christoffer Dall <christoffer.dall@...aro.org>
To:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org,
	kernel-hardening@...ts.openwall.com, will.deacon@....com,
	catalin.marinas@....com, mark.rutland@....com,
	leif.lindholm@...aro.org, keescook@...omium.org,
	linux-kernel@...r.kernel.org, stuart.yoder@...escale.com,
	bhupesh.sharma@...escale.com, arnd@...db.de, marc.zyngier@....com
Subject: Re: [PATCH v2 02/13] arm64: introduce KIMAGE_VADDR as the virtual
 base of the kernel region

On Wed, Dec 30, 2015 at 04:26:01PM +0100, Ard Biesheuvel wrote:
> This introduces the preprocessor symbol KIMAGE_VADDR which will serve as
> the symbolic virtual base of the kernel region, i.e., the kernel's virtual
> offset will be KIMAGE_VADDR + TEXT_OFFSET. For now, we define it as being
> equal to PAGE_OFFSET, but in the future, it will be moved below it once
> we move the kernel virtual mapping out of the linear mapping.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> ---
>  arch/arm64/include/asm/memory.h | 10 ++++++++--
>  arch/arm64/kernel/head.S        |  2 +-
>  arch/arm64/kernel/vmlinux.lds.S |  4 ++--
>  3 files changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index 853953cd1f08..bea9631b34a8 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -51,7 +51,8 @@
>  #define VA_BITS			(CONFIG_ARM64_VA_BITS)
>  #define VA_START		(UL(0xffffffffffffffff) << VA_BITS)
>  #define PAGE_OFFSET		(UL(0xffffffffffffffff) << (VA_BITS - 1))
> -#define MODULES_END		(PAGE_OFFSET)
> +#define KIMAGE_VADDR		(PAGE_OFFSET)
> +#define MODULES_END		(KIMAGE_VADDR)
>  #define MODULES_VADDR		(MODULES_END - SZ_64M)
>  #define PCI_IO_END		(MODULES_VADDR - SZ_2M)
>  #define PCI_IO_START		(PCI_IO_END - PCI_IO_SIZE)
> @@ -75,8 +76,13 @@
>   * private definitions which should NOT be used outside memory.h
>   * files.  Use virt_to_phys/phys_to_virt/__pa/__va instead.
>   */
> -#define __virt_to_phys(x)	(((phys_addr_t)(x) - PAGE_OFFSET + PHYS_OFFSET))
> +#define __virt_to_phys(x) ({						\
> +	phys_addr_t __x = (phys_addr_t)(x);				\
> +	__x >= PAGE_OFFSET ? (__x - PAGE_OFFSET + PHYS_OFFSET) :	\
> +			     (__x - KIMAGE_VADDR + PHYS_OFFSET); })

so __virt_to_phys will now work with a subset of the non-linear namely
all except vmalloced and ioremapped ones?

> +
>  #define __phys_to_virt(x)	((unsigned long)((x) - PHYS_OFFSET + PAGE_OFFSET))
> +#define __phys_to_kimg(x)	((unsigned long)((x) - PHYS_OFFSET + KIMAGE_VADDR))
>  
>  /*
>   * Convert a page to/from a physical address
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index 23cfc08fc8ba..6434c844a0e4 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -389,7 +389,7 @@ __create_page_tables:
>  	 * Map the kernel image (starting with PHYS_OFFSET).
>  	 */
>  	mov	x0, x26				// swapper_pg_dir
> -	mov	x5, #PAGE_OFFSET
> +	ldr	x5, =KIMAGE_VADDR
>  	create_pgd_entry x0, x5, x3, x6
>  	ldr	x6, =KERNEL_END			// __va(KERNEL_END)
>  	mov	x3, x24				// phys offset
> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> index 7de6c39858a5..ced0dedcabcc 100644
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -88,7 +88,7 @@ SECTIONS
>  		*(.discard.*)
>  	}
>  
> -	. = PAGE_OFFSET + TEXT_OFFSET;
> +	. = KIMAGE_VADDR + TEXT_OFFSET;
>  
>  	.head.text : {
>  		_text = .;
> @@ -185,4 +185,4 @@ ASSERT(__idmap_text_end - (__idmap_text_start & ~(SZ_4K - 1)) <= SZ_4K,
>  /*
>   * If padding is applied before .head.text, virt<->phys conversions will fail.
>   */
> -ASSERT(_text == (PAGE_OFFSET + TEXT_OFFSET), "HEAD is misaligned")
> +ASSERT(_text == (KIMAGE_VADDR + TEXT_OFFSET), "HEAD is misaligned")
> -- 
> 2.5.0
> 
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