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From: Kees Cook <kees.cook@canonical.com>
To: matthieu castet <castet.matthieu@free.fr>
Cc: Linux Kernel list <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@elte.hu>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [BUG] broken ebba638ae723d8a8fc2f7abce5ec18b688b791d7
Date: Thu, 27 Jan 2011 15:00:13 -0800	[thread overview]
Message-ID: <20110127230013.GO4981@outflux.net> (raw)
In-Reply-To: <4D41E86D.8060205@free.fr>

Hi matthieu,

On Thu, Jan 27, 2011 at 10:49:33PM +0100, matthieu castet wrote:
> ebba638ae723d8a8fc2f7abce5ec18b688b791d7 x86, cpu: Call verify_cpu during 32bit CPU startup look buggy.
> 
> It add a call to verify_cpu, but we never set the stack before (I check with qemu + gdbserver that sp is random
> when doing cpu hotplug).
> This mean do randomly corrupt the memory.

Yikes, good catch.

arch/x86/kernel/trampoline_64.S uses:
        movw    $(trampoline_stack_end - r_base), %sp

arch/x86/boot/compressed/head_64.S uses:
        movl    $boot_stack_end, %eax
        addl    %ebp, %eax
        movl    %eax, %esp

what would be safe for arch/x86/kernel/head_32.S ? It uses "stack_start",
but later after paging set-up. Is the following sane to solve this?


diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index fc293dc..8ddd0e4 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -284,6 +284,8 @@ ENTRY(startup_32_smp)
 	movl %eax,%gs
 #endif /* CONFIG_SMP */
 default_entry:
+	/* Set up the stack pointer */
+	lss stack_start,%esp
 
 /*
  *	New page tables may be in 4Mbyte page mode and may
@@ -347,8 +349,6 @@ default_entry:
 	movl %eax,%cr0		/* ..and set paging (PG) bit */
 	ljmp $__BOOT_CS,$1f	/* Clear prefetch and normalize %eip */
 1:
-	/* Set up the stack pointer */
-	lss stack_start,%esp
 
 /*
  * Initialize eflags.  Some BIOS's leave bits like NT set.  This would

-Kees


-- 
Kees Cook
Ubuntu Security Team

  reply	other threads:[~2011-01-27 23:00 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-27 21:49 matthieu castet
2011-01-27 23:00 ` Kees Cook [this message]
2011-01-28  2:24   ` H. Peter Anvin
2011-01-28  3:38     ` H. Peter Anvin
2011-01-28 16:58       ` Jeremy Fitzhardinge
2011-02-02 22:48         ` H. Peter Anvin
2011-02-03  1:19           ` Rusty Russell
2011-02-03  2:00             ` Rusty Russell
2011-02-03  2:35               ` H. Peter Anvin
2011-02-03 10:02                 ` Rusty Russell
2011-02-03 17:11                   ` H. Peter Anvin
2011-01-31 21:38     ` Kees Cook
2011-01-31 23:11       ` matthieu castet
2011-01-31 23:17         ` Rafael J. Wysocki
2011-02-01 13:07           ` castet.matthieu
2011-02-01 18:50             ` Rafael J. Wysocki
2011-01-31 23:52         ` Kees Cook
2011-02-01  1:10           ` H. Peter Anvin
2011-02-02 20:40             ` Kees Cook
2011-02-04  5:47               ` H. Peter Anvin
2011-01-31 23:12       ` matthieu castet
2011-02-05  0:34 ` [tip:x86/urgent] x86-32: Make sure the stack is set up before we use it tip-bot for H. Peter Anvin
2011-02-05  0:45 ` tip-bot for H. Peter Anvin
2011-02-05  2:19   ` Kees Cook
2011-02-05  4:37     ` H. Peter Anvin
2011-02-05  5:37       ` Kees Cook
2011-02-05  6:26         ` H. Peter Anvin
2011-02-05  6:31 ` tip-bot for H. Peter Anvin

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