linux-kernel - Re: [PATCH] x86/mm: Fix ELF_ET_DYN

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Date:   Thu, 9 Nov 2017 13:38:12 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Kees Cook <keescook@...omium.org>, Ingo Molnar <mingo@...e.hu>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Nicholas Piggin <npiggin@...il.com>
Subject: Re: [PATCH] x86/mm: Fix ELF_ET_DYN_BASE for 5-level paging

On Tue, Nov 07, 2017 at 01:38:04PM +0300, Kirill A. Shutemov wrote:
> On machines with 5-level paging we don't want to allocate mapping above
> 47-bit unless user explicitly asked for it. See b569bab78d8d ("x86/mm:
> Prepare to expose larger address space to userspace") for details.
> 
> c715b72c1ba4 ("mm: revert x86_64 and arm64 ELF_ET_DYN_BASE base
> changes") broke the behaviour. After the commit elf binary and heap got
> mapped above 47-bits.
> 
> Let's fix this.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Fixes: c715b72c1ba4 ("mm: revert x86_64 and arm64 ELF_ET_DYN_BASE base changes")
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Nicholas Piggin <npiggin@...il.com>

Folks, can we please get this applied?

Without the change on 5-level paging machine we will have elf binary and
heap mapped above 47-bit by default. This may lead to userspace brakage.

> ---
>  arch/x86/include/asm/elf.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h
> index c1a125e47ff3..3a091cea36c5 100644
> --- a/arch/x86/include/asm/elf.h
> +++ b/arch/x86/include/asm/elf.h
> @@ -253,7 +253,7 @@ extern int force_personality32;
>   * space open for things that want to use the area for 32-bit pointers.
>   */
>  #define ELF_ET_DYN_BASE		(mmap_is_ia32() ? 0x000400000UL : \
> -						  (TASK_SIZE / 3 * 2))
> +						  (DEFAULT_MAP_WINDOW / 3 * 2))
>  
>  /* This yields a mask that user programs can use to figure out what
>     instruction set this CPU supports.  This could be done in user space,
> -- 
> 2.14.2
> 
> --
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-- 
 Kirill A. Shutemov