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From: Michal Hocko <mhocko@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>
Cc: Jiri Kosina <jkosina@suse.cz>, Andi Kleen <ak@linux.intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-mm@kvack.org, x86@kernel.org
Subject: Re: [RFC PATCH] mmap, aslr: do not enforce legacy mmap on unlimited stacks
Date: Fri, 23 Jun 2017 10:46:19 +0200	[thread overview]
Message-ID: <20170623084619.GI5308@dhcp22.suse.cz> (raw)
In-Reply-To: <20170614082218.12450-1-mhocko@kernel.org>

ping?

On Wed 14-06-17 10:22:18, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
> 
> Since cc503c1b43e0 ("x86: PIE executable randomization") we treat
> applications with RLIMIT_STACK configured to unlimited as legacy
> and so we a) set the mmap_base to 1/3 of address space + randomization
> and b) mmap from bottom to top. This makes some sense as it allows the
> stack to grow really large. On the other hand it reduces the address
> space usable for default mmaps (wihout address hint) quite a lot. We
> have received a bug report that SAP HANA workload has hit into this
> limitation.
> 
> We could argue that the user just got what he asked for when setting
> up the unlimited stack but to be realistic growing stack up to 1/6
> TASK_SIZE (allowed by mmap_base) is pretty much unimited in the real
> life. This would give mmap 20TB of additional address space which is
> quite nice. Especially when it is much more likely to use that address
> space than the reserved stack.
> 
> Digging into the history the original implementation of the
> randomization 8817210d4d96 ("[PATCH] x86_64: Flexmap for 32bit and
> randomized mappings for 64bit") didn't have this restriction.
> 
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
> 
> Hi,
> I am sending this as a RFC because I am not really sure how to deal with
> this. We might as well ignore the reported issue and claim "do not use
> unlimited stacks" and be done with it. I just stroke me as an unexpected
> behavior.
> 
>  arch/x86/mm/mmap.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> index 19ad095b41df..797295e792b2 100644
> --- a/arch/x86/mm/mmap.c
> +++ b/arch/x86/mm/mmap.c
> @@ -74,9 +74,6 @@ static int mmap_is_legacy(void)
>  	if (current->personality & ADDR_COMPAT_LAYOUT)
>  		return 1;
>  
> -	if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
> -		return 1;
> -
>  	return sysctl_legacy_va_layout;
>  }
>  
> -- 
> 2.11.0
> 

-- 
Michal Hocko
SUSE Labs

WARNING: multiple messages have this Message-ID (diff)
From: Michal Hocko <mhocko@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>
Cc: Jiri Kosina <jkosina@suse.cz>, Andi Kleen <ak@linux.intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-mm@kvack.org, x86@kernel.org
Subject: Re: [RFC PATCH] mmap, aslr: do not enforce legacy mmap on unlimited stacks
Date: Fri, 23 Jun 2017 10:46:19 +0200	[thread overview]
Message-ID: <20170623084619.GI5308@dhcp22.suse.cz> (raw)
In-Reply-To: <20170614082218.12450-1-mhocko@kernel.org>

ping?

On Wed 14-06-17 10:22:18, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
> 
> Since cc503c1b43e0 ("x86: PIE executable randomization") we treat
> applications with RLIMIT_STACK configured to unlimited as legacy
> and so we a) set the mmap_base to 1/3 of address space + randomization
> and b) mmap from bottom to top. This makes some sense as it allows the
> stack to grow really large. On the other hand it reduces the address
> space usable for default mmaps (wihout address hint) quite a lot. We
> have received a bug report that SAP HANA workload has hit into this
> limitation.
> 
> We could argue that the user just got what he asked for when setting
> up the unlimited stack but to be realistic growing stack up to 1/6
> TASK_SIZE (allowed by mmap_base) is pretty much unimited in the real
> life. This would give mmap 20TB of additional address space which is
> quite nice. Especially when it is much more likely to use that address
> space than the reserved stack.
> 
> Digging into the history the original implementation of the
> randomization 8817210d4d96 ("[PATCH] x86_64: Flexmap for 32bit and
> randomized mappings for 64bit") didn't have this restriction.
> 
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
> 
> Hi,
> I am sending this as a RFC because I am not really sure how to deal with
> this. We might as well ignore the reported issue and claim "do not use
> unlimited stacks" and be done with it. I just stroke me as an unexpected
> behavior.
> 
>  arch/x86/mm/mmap.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> index 19ad095b41df..797295e792b2 100644
> --- a/arch/x86/mm/mmap.c
> +++ b/arch/x86/mm/mmap.c
> @@ -74,9 +74,6 @@ static int mmap_is_legacy(void)
>  	if (current->personality & ADDR_COMPAT_LAYOUT)
>  		return 1;
>  
> -	if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
> -		return 1;
> -
>  	return sysctl_legacy_va_layout;
>  }
>  
> -- 
> 2.11.0
> 

-- 
Michal Hocko
SUSE Labs

--
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  reply	other threads:[~2017-06-23  8:46 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-06-14  8:22 [RFC PATCH] mmap, aslr: do not enforce legacy mmap on unlimited stacks Michal Hocko
2017-06-14  8:22 ` Michal Hocko
2017-06-23  8:46 ` Michal Hocko [this message]
2017-06-23  8:46   ` Michal Hocko
2017-06-23 14:02 ` [tip:x86/mm] x86/mmap, ASLR: Do not treat unlimited-stack tasks as legacy mmap tip-bot for Michal Hocko
2017-06-23 14:54   ` Oleg Nesterov
2017-06-27  8:00     ` Jiri Kosina
2017-06-27 14:22       ` Oleg Nesterov
2017-06-28  9:40         ` Jiri Kosina
2017-06-23 20:35   ` Jiri Kosina
2017-06-24  6:43   ` tip-bot for Michal Hocko

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