From: Andrew Morton <akpm@linux-foundation.org>
To: Kees Cook <keescook@chromium.org>
Cc: Andy Lutomirski <luto@kernel.org>, Jann Horn <jannh@google.com>,
Ingo Molnar <mingo@kernel.org>, Laura Abbott <labbott@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Al Viro <viro@zeniv.linux.org.uk>,
Sahara <keun-o.park@darkmatter.ae>,
"Levin, Alexander (Sasha Levin)" <alexander.levin@verizon.com>,
Michal Hocko <mhocko@suse.com>,
Andrea Arcangeli <aarcange@redhat.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
linux-kernel@vger.kernel.org,
kernel-hardening@lists.openwall.com
Subject: Re: [PATCH] fork: Allow stack to be wiped on fork
Date: Tue, 20 Feb 2018 16:31:42 -0800 [thread overview]
Message-ID: <20180220163142.15366a82a7bece715b997597@linux-foundation.org> (raw)
In-Reply-To: <20180117055015.GA15256@beast>
On Tue, 16 Jan 2018 21:50:15 -0800 Kees Cook <keescook@chromium.org> wrote:
> One of the classes of kernel stack content leaks is exposing the contents
> of prior heap or stack contents when a new process stack is allocated.
> Normally, those stacks are not zeroed, and the old contents remain in
> place. With some types of stack content exposure flaws, those contents
> can leak to userspace. Kernels built with CONFIG_CLEAR_STACK_FORK will
> no longer be vulnerable to this, as the stack will be wiped each time
> a stack is assigned to a new process. There's not a meaningful change
> in runtime performance; it almost looks like it provides a benefit.
>
> Performing back-to-back kernel builds before:
> Run times: 157.86 157.09 158.90 160.94 160.80
> Mean: 159.12
> Std Dev: 1.54
>
> With CONFIG_CLEAR_STACK_FORK=y:
> Run times: 159.31 157.34 156.71 158.15 160.81
> Mean: 158.46
> Std Dev: 1.46
>
> ...
>
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -904,6 +904,14 @@ config VMAP_STACK
> the stack to map directly to the KASAN shadow map using a formula
> that is incorrect if the stack is in vmalloc space.
>
> +config CLEAR_STACK_FORK
> + bool "Clear the kernel stack at each fork"
> + help
> + To resist stack content leak flaws, this clears newly allocated
> + kernel stacks to keep previously freed heap or stack contents
> + from being present in the new stack. This has almost no
> + measurable performance impact.
> +
It would be much nicer to be able to control this at runtime rather
than compile-time. Why not a /proc tunable? We could always use more
of those ;)
next prev parent reply other threads:[~2018-02-21 0:31 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-17 5:50 [PATCH] fork: Allow stack to be wiped on fork Kees Cook
2018-01-17 9:17 ` Michal Hocko
2018-01-19 19:16 ` [kernel-hardening] " Laura Abbott
2018-01-26 22:01 ` Jiri Kosina
2018-01-26 22:31 ` Jiri Kosina
2018-02-21 0:31 ` Andrew Morton [this message]
2018-02-21 1:56 ` Andy Lutomirski
2018-02-22 9:47 ` Mel Gorman
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