linux-kernel - Re: [PATCH][v3.2] Revert: x86, 64bit, mm: Mark data/bss/brk to nx

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Date:	Mon, 19 Jan 2015 22:07:11 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	stable <stable@...r.kernel.org>, Yinghai Lu <yinghai@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH][v3.2] Revert: x86, 64bit, mm: Mark data/bss/brk to nx

On Mon, 2015-01-19 at 16:49 -0500, Steven Rostedt wrote:
> Testing v3.2-rt I found that after merging the latest v3.2 stable tree,
> hotplug stopped working. I tested the latest v3.2 stable, and it was
> not working there either. I bisected it down to:
> 
> commit e105c8187b7101e8a8a54ac0218c9d9c9463c636
> Author: Yinghai Lu <yinghai@...nel.org>
> Date:   Thu Jan 24 12:20:13 2013 -0800
> 
>     x86, 64bit, mm: Mark data/bss/brk to nx
>     
>     commit 72212675d1c96f5db8ec6fb35701879911193158 upstream.
> 
> Simply doing:
> 
>  # echo 0 > /sys/devices/system/cpu/cpu1/online
>  # echo 1 > /sys/devices/system/cpu/cpu1/online
> 
> caused the system to reboot.
> 
> After reverting that commit, hotplug works again on the v3.2 stable
> tree.

Yes, I know this needs fixing.  It also broke suspend/resume on SMP
machines since that involves offlining and onlining CPUs 1-n.

Ben.

> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 266f71719e42..783eba48d00c 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -778,7 +778,6 @@ void mark_rodata_ro(void)
>  	unsigned long text_end = PAGE_ALIGN((unsigned long) &__stop___ex_table);
>  	unsigned long rodata_end = PAGE_ALIGN((unsigned long) &__end_rodata);
>  	unsigned long data_start = (unsigned long) &_sdata;
> -	unsigned long all_end;
>  
>  	printk(KERN_INFO "Write protecting the kernel read-only data: %luk\n",
>  	       (end - start) >> 10);
> @@ -787,8 +786,8 @@ void mark_rodata_ro(void)
>  	kernel_set_to_readonly = 1;
>  
>  	/*
> -	 * The rodata/data/bss/brk section (but not the kernel text!)
> -	 * should also be not-executable.
> +	 * The rodata section (but not the kernel text!) should also be
> +	 * not-executable.
>  	 *
>  	 * We align all_end to PMD_SIZE because the existing mapping
>  	 * is a full PMD. If we would align _brk_end to PAGE_SIZE we
> @@ -798,8 +797,7 @@ void mark_rodata_ro(void)
>  	 * Any PMD which was setup after the one which covers _brk_end
>  	 * has been zapped already via cleanup_highmem().
>  	 */
> -	all_end = roundup((unsigned long)_brk_end, PMD_SIZE);
> -	set_memory_nx(rodata_start, (all_end - rodata_start) >> PAGE_SHIFT);
> +	set_memory_nx(rodata_start, (end - rodata_start) >> PAGE_SHIFT);
>  
>  	rodata_test();
>  

-- 
Ben Hutchings
Larkinson's Law: All laws are basically false.

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