linux-kernel - Re: [PATCH v2 06/13] fork: Add generic vmalloced stack support

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Message-ID: <20160617205728.qgha2qeubdkg73uh@treble>
Date:	Fri, 17 Jun 2016 15:57:28 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
	Nadav Amit <nadav.amit@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Brian Gerst <brgerst@...il.com>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jann Horn <jann@...jh.net>,
	Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH v2 06/13] fork: Add generic vmalloced stack support

On Fri, Jun 17, 2016 at 01:00:42PM -0700, Andy Lutomirski wrote:
> @@ -213,24 +232,46 @@ struct kmem_cache *vm_area_cachep;
>  /* SLAB cache for mm_struct structures (tsk->mm) */
>  static struct kmem_cache *mm_cachep;
>  
> -static void account_kernel_stack(struct thread_info *ti, int account)
> +static void account_kernel_stack(struct task_struct *tsk, int account)
>  {
> -	struct zone *zone = page_zone(virt_to_page(ti));
> +	struct zone *zone;
> +	struct thread_info *ti = task_thread_info(tsk);
> +	struct vm_struct *vm = task_stack_vm_area(tsk);
> +
> +	BUILD_BUG_ON(IS_ENABLED(CONFIG_VMAP_STACK) && PAGE_SIZE % 1024 != 0);
> +
> +	if (vm) {
> +		int i;
>  
> -	mod_zone_page_state(zone, NR_KERNEL_STACK_KB,
> -			    THREAD_SIZE / 1024 * account);
> +		BUG_ON(vm->nr_pages != THREAD_SIZE / PAGE_SIZE);
>  
> -	/* All stack pages belong to the same memcg. */
> -	memcg_kmem_update_page_stat(
> -		virt_to_page(ti), MEMCG_KERNEL_STACK,
> -		account * (THREAD_SIZE / PAGE_SIZE));
> +		for (i = 0; i < THREAD_SIZE / PAGE_SIZE; i++) {
> +			mod_zone_page_state(page_zone(vm->pages[i]),
> +					    1, PAGE_SIZE / 1024 * account);

Shouldn't the second argument be NR_KERNEL_STACK_KB instead of 1?

-- 
Josh