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SubjectRe: [BUG] broken ebba638ae723d8a8fc2f7abce5ec18b688b791d7
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


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
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