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From: "H. Peter Anvin" <hpa@zytor.com>
To: Kees Cook <kees.cook@canonical.com>
Cc: matthieu castet <castet.matthieu@free.fr>,
	Linux Kernel list <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@elte.hu>
Subject: Re: [BUG] broken ebba638ae723d8a8fc2f7abce5ec18b688b791d7
Date: Thu, 27 Jan 2011 18:24:14 -0800	[thread overview]
Message-ID: <4D4228CE.5090601@zytor.com> (raw)
In-Reply-To: <20110127230013.GO4981@outflux.net>

On 01/27/2011 03:00 PM, Kees Cook wrote:
>
> 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?
>

To run it before paging is set up, you can't use stack, start; you have 
to use a pointer based on physical address.  You have two problems with 
using stack_start: you're using a linear address to access stack_start, 
and stack_start itself contains a linear address.

It's not entirely clear to me why we don't initialize %ss to __BOOT_DS 
with the other segment registers, but it would make most sense to me:

diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index fc293dc..c10f9ba 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -99,7 +99,12 @@ ENTRY(startup_32)
         movl %eax,%es
         movl %eax,%fs
         movl %eax,%gs
+       movl %eax,%ss
  2:
+/*
+ * Set up an initial stack
+ */
+       movl $pa(init_thread_union+THREAD_SIZE), %esp

  /*
   * Clear BSS first so that there are no surprises...

	-hpa

  reply	other threads:[~2011-01-28  2:24 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
2011-01-28  2:24   ` H. Peter Anvin [this message]
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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