Re: [PATCH] x86/mm: Fix ELF_ET_DYN_BASE for 5-level paging

From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Ingo Molnar <mingo@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Kees Cook <keescook@chromium.org>, Ingo Molnar <mingo@elte.hu>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH] x86/mm: Fix ELF_ET_DYN_BASE for 5-level paging
Date: Thu, 9 Nov 2017 13:38:12 +0300	[thread overview]
Message-ID: <20171109103812.tr3o5ujwokg5s6c6@node.shutemov.name> (raw)
In-Reply-To: <20171107103804.47341-1-kirill.shutemov@linux.intel.com>

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@linux.intel.com>
> Fixes: c715b72c1ba4 ("mm: revert x86_64 and arm64 ELF_ET_DYN_BASE base changes")
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Nicholas Piggin <npiggin@gmail.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