Re: [PATCH 08/11] x86: make TASK_SIZE_MAX usable from assembly code

Kees Cook
2020-08-18T19:45:07Z

On Mon, Aug 17, 2020 at 09:32:09AM +0200, Christoph Hellwig wrote:
> For 64-bit the only hing missing was a strategic _AC, and for 32-bit we

typo: thing

> need to use __PAGE_OFFSET instead of PAGE_OFFSET in the TASK_SIZE
> definition to escape the explicit unsigned long cast. This just works
> because __PAGE_OFFSET is defined using _AC itself and thus never needs
> the cast anyway.

Shouldn't this be folded into the prior patch so there's no bisection
problem?

-Kees

>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> arch/x86/include/asm/page_32_types.h | 4 ++--
> arch/x86/include/asm/page_64_types.h | 2 +-
> 2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/include/asm/page_32_types.h b/arch/x86/include/asm/page_32_types.h
> index 26236925fb2c36..f462895a33e452 100644
> --- a/arch/x86/include/asm/page_32_types.h
> +++ b/arch/x86/include/asm/page_32_types.h
> @@ -44,8 +44,8 @@
> /*
> * User space process size: 3GB (default).
> */
> -#define IA32_PAGE_OFFSET PAGE_OFFSET
> -#define TASK_SIZE PAGE_OFFSET
> +#define IA32_PAGE_OFFSET __PAGE_OFFSET
> +#define TASK_SIZE __PAGE_OFFSET
> #define TASK_SIZE_LOW TASK_SIZE
> #define TASK_SIZE_MAX TASK_SIZE
> #define DEFAULT_MAP_WINDOW TASK_SIZE
> diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h
> index 996595c9897e0a..838515daf87b36 100644
> --- a/arch/x86/include/asm/page_64_types.h
> +++ b/arch/x86/include/asm/page_64_types.h
> @@ -76,7 +76,7 @@
> *
> * With page table isolation enabled, we map the LDT in ... [stay tuned]
> */
> -#define TASK_SIZE_MAX ((1UL << __VIRTUAL_MASK_SHIFT) - PAGE_SIZE)
> +#define TASK_SIZE_MAX ((_AC(1,UL) << __VIRTUAL_MASK_SHIFT) - PAGE_SIZE)
>
> #define DEFAULT_MAP_WINDOW ((1UL << 47) - PAGE_SIZE)
>
> --
> 2.28.0
>

--
Kees Cook