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

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Date:	Mon, 19 Jan 2015 16:49:26 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	stable <stable@...r.kernel.org>, Yinghai Lu <yinghai@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH][v3.2] Revert: x86, 64bit, mm: Mark data/bss/brk to nx


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.

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();
 
--
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