Re: [PATCH v11 09/24] arm64: move untagged_addr macro from uaccess.h to memory.h

Mark Rutland
2018-11-23T17:37:50Z

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@google.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@arm.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
>