linux-kernel - Re: [PATCH v11 09/24] arm64: move untagged

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Message-ID: <20181123173739.osgvnnhmptdgtlnl@lakrids.cambridge.arm.com>
Date:   Fri, 23 Nov 2018 17:37:39 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Dave Martin <dave.martin@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Ingo Molnar <mingo@...nel.org>,
        Paul Lawrence <paullawrence@...gle.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        kasan-dev@...glegroups.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-sparse@...r.kernel.org, linux-mm@...ck.org,
        linux-kbuild@...r.kernel.org, Kostya Serebryany <kcc@...gle.com>,
        Evgeniy Stepanov <eugenis@...gle.com>,
        Lee Smith <Lee.Smith@....com>,
        Ramana Radhakrishnan <Ramana.Radhakrishnan@....com>,
        Jacob Bramley <Jacob.Bramley@....com>,
        Ruben Ayrapetyan <Ruben.Ayrapetyan@....com>,
        Jann Horn <jannh@...gle.com>,
        Mark Brand <markbrand@...gle.com>,
        Chintan Pandya <cpandya@...eaurora.org>,
        Vishwath Mohan <vishwath@...gle.com>
Subject: Re: [PATCH v11 09/24] arm64: move untagged_addr macro from uaccess.h
 to memory.h

On Mon, Nov 19, 2018 at 06:26:25PM +0100, Andrey Konovalov wrote:
> Move the untagged_addr() macro from arch/arm64/include/asm/uaccess.h
> to arch/arm64/include/asm/memory.h to be later reused by KASAN.
> 
> Also make the untagged_addr() macro accept all kinds of address types
> (void *, unsigned long, etc.). This allows not to specify type casts in
> each place where the macro is used. This is done by using __typeof__.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> ---
>  arch/arm64/include/asm/memory.h  | 8 ++++++++
>  arch/arm64/include/asm/uaccess.h | 7 -------
>  2 files changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index 05fbc7ffcd31..deb95be44392 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -73,6 +73,14 @@
>  #define KERNEL_START      _text
>  #define KERNEL_END        _end
>  
> +/*
> + * When dealing with data aborts, watchpoints, or instruction traps we may end
> + * up with a tagged userland pointer. Clear the tag to get a sane pointer to
> + * pass on to access_ok(), for instance.
> + */
> +#define untagged_addr(addr)	\
> +	(__typeof__(addr))sign_extend64((__u64)(addr), 55)

Minor nits:

* s/__u64/u64/ (or s/__u64/unsigned long/), since this isn't a UAPI
  header.

* Please move this down into the #ifndef __ASSEMBLY__ block, after we
  include <linux/bitops.h>, which is necessary for sign_extend64().

With those fixed up, this patch looks sound to me:

Acked-by: Mark Rutland <mark.rutland@....com>

Thanks,
Mark.

> +
>  /*
>   * Generic and tag-based KASAN require 1/8th and 1/16th of the kernel virtual
>   * address space for the shadow region respectively. They can bloat the stack
> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> index 07c34087bd5e..281a1e47263d 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -96,13 +96,6 @@ static inline unsigned long __range_ok(const void __user *addr, unsigned long si
>  	return ret;
>  }
>  
> -/*
> - * When dealing with data aborts, watchpoints, or instruction traps we may end
> - * up with a tagged userland pointer. Clear the tag to get a sane pointer to
> - * pass on to access_ok(), for instance.
> - */
> -#define untagged_addr(addr)		sign_extend64(addr, 55)
> -
>  #define access_ok(type, addr, size)	__range_ok(addr, size)
>  #define user_addr_max			get_fs
>  
> -- 
> 2.19.1.1215.g8438c0b245-goog
>