kernel-hardening - Re: [PATCH] fork: Allow stack to be wiped on fork

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Message-ID: <alpine.LRH.2.00.1801262259300.27010@gjva.wvxbf.pm>
Date: Fri, 26 Jan 2018 23:01:21 +0100 (CET)
From: Jiri Kosina <jikos@...nel.org>
To: Kees Cook <keescook@...omium.org>
cc: Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>, Jann Horn <jannh@...gle.com>,
        Ingo Molnar <mingo@...nel.org>, Laura Abbott <labbott@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Al Viro <viro@...iv.linux.org.uk>, Sahara <keun-o.park@...kmatter.ae>,
        "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>,
        Michal Hocko <mhocko@...e.com>, Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH] fork: Allow stack to be wiped on fork

On Tue, 16 Jan 2018, Kees Cook wrote:

> diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h
> index 34f053a150a9..091f53fe31cc 100644
> --- a/include/linux/thread_info.h
> +++ b/include/linux/thread_info.h
> @@ -43,7 +43,9 @@ enum {
>  #define THREAD_ALIGN	THREAD_SIZE
>  #endif
>  
> -#if IS_ENABLED(CONFIG_DEBUG_STACK_USAGE) || IS_ENABLED(CONFIG_DEBUG_KMEMLEAK)
> +#if IS_ENABLED(CONFIG_DEBUG_STACK_USAGE) || \
> +    IS_ENABLED(CONFIG_DEBUG_KMEMLEAK) || \
> +    IS_ENABLED(CONFIG_CLEAR_STACK_FORK)
>  # define THREADINFO_GFP		(GFP_KERNEL_ACCOUNT | __GFP_ZERO)
>  #else
>  # define THREADINFO_GFP		(GFP_KERNEL_ACCOUNT)
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 2295fc69717f..215b1ce2b2cd 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -215,7 +215,7 @@ static unsigned long *alloc_thread_stack_node(struct task_struct *tsk, int node)
>  		if (!s)
>  			continue;
>  
> -#ifdef CONFIG_DEBUG_KMEMLEAK
> +#if IS_ENABLED(CONFIG_DEBUG_KMEMLEAK) || IS_ENABLED(CONFIG_CLEAR_STACK_FORK)
>  		/* Clear stale pointers from reused stack. */
>  		memset(s->addr, 0, THREAD_SIZE);
>  #endif

Is there any good reason not to do it symmetricaly also for non-vmapped 
stacks? (by passing __GFP_ZERO to alloc_pages_node())?

Thanks,

-- 
Jiri Kosina
SUSE Labs

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