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From: matthieu castet <castet.matthieu@free.fr>
To: Kees Cook <kees.cook@canonical.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
	Linux Kernel list <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@elte.hu>,
	Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: [BUG] broken ebba638ae723d8a8fc2f7abce5ec18b688b791d7
Date: Tue, 01 Feb 2011 00:11:16 +0100	[thread overview]
Message-ID: <4D474194.2000709@free.fr> (raw)
In-Reply-To: <20110131213847.GF4557@outflux.net>

[-- Attachment #1: Type: text/plain, Size: 1809 bytes --]

Kees Cook a écrit :
> Hi,
> 
> On Thu, Jan 27, 2011 at 06:24:14PM -0800, H. Peter Anvin wrote:
>> 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...
> 
> This doesn't appear to work for me. While I can boot fine, doing CPU
> hotplugging hangs the system. :(
> 
This is weird because the patch only touch first cpu (startup_32 entry) and cpu hotplug go to 
startup_32_smp.

Here a untested patch that move the stack setup in the common path.


Matthieu



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diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index fc293dc..5df3432 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -284,6 +284,12 @@ ENTRY(startup_32_smp)
 	movl %eax,%gs
 #endif /* CONFIG_SMP */
 default_entry:
+	/*
+	 * Set up an initial stack
+	 */
+	movl $(__BOOT_DS),%eax
+	movl %eax,%ss
+	movl $pa(init_thread_union+THREAD_SIZE), %esp
 
 /*
  *	New page tables may be in 4Mbyte page mode and may

  reply	other threads:[~2011-01-31 23:11 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
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 [this message]
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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