Re: [PATCH v2] arm64: compat: Reduce address limit

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On Mon, Apr 01, 2019 at 12:30:14PM +0100, Vincenzo Frascino wrote:
> Currently, compat tasks running on arm64 can allocate memory up to
> TASK_SIZE_32 (UL(0x100000000)).
> 
> This means that mmap() allocations, if we treat them as returning an
> array, are not compliant with the sections 6.5.8 of the C standard
> (C99) which states that: "If the expression P points to an element of
> an array object and the expression Q points to the last element of the
> same array object, the pointer expression Q+1 compares greater than P".
> 
> Redefine TASK_SIZE_32 to address the issue.
> 
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: Jann Horn <jannh@xxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Reported-by: Jann Horn <jannh@xxxxxxxxxx>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
> ---
>  arch/arm64/include/asm/processor.h | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
> index 5d9ce62bdebd..9c831d9d3cd2 100644
> --- a/arch/arm64/include/asm/processor.h
> +++ b/arch/arm64/include/asm/processor.h
> @@ -57,7 +57,15 @@
>  #define TASK_SIZE_64		(UL(1) << vabits_user)
>  
>  #ifdef CONFIG_COMPAT
> +#ifdef CONFIG_ARM64_64K_PAGES
> +/*
> + * With CONFIG_ARM64_64K_PAGES enabled, the last page is occupied
> + * by the compact vectors page.

s/compact/compat/

Will



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