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SubjectRe: [BUG] broken ebba638ae723d8a8fc2f7abce5ec18b688b791d7
On 02/02/2011 12:40 PM, Kees Cook wrote:
> On Mon, Jan 31, 2011 at 05:10:03PM -0800, H. Peter Anvin wrote:
>> On 01/31/2011 03:52 PM, Kees Cook wrote:
>>>
>>> This worked, thanks! If this tests cleanly for you in qemu, we should get
>>> this committed.
>>>
>>
>> This is wrong for at least one reason; possibly two:
>>
>> a) it ignores the control to not reload the segment registers (not
>> sure if anything still uses them, but...)
>>
>> b) I'm not sure that init_thread_union is safe for the non-BSP CPU here.
>
> What's the best way to move forward? Or, how can we find answers to these
> questions?
>
> -Kees
>


Can someone test out the attached patch and verify that it works?

-hpa

--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.

diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index fc293dc..2aee594 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -26,6 +26,11 @@
#define pa(X) ((X) - __PAGE_OFFSET)

/*
+ * Initial stack pointer for the boot processor
+ */
+initial_stack_pointer = init_thread_union+THREAD_SIZE
+
+/*
* References to members of the new_cpu_data structure.
*/

@@ -99,8 +104,10 @@ ENTRY(startup_32)
movl %eax,%es
movl %eax,%fs
movl %eax,%gs
+ movl %eax,%ss
2:
-
+ movl $pa(initial_stack_pointer), %esp
+
/*
* Clear BSS first so that there are no surprises...
*/
@@ -282,6 +289,9 @@ ENTRY(startup_32_smp)
movl %eax,%es
movl %eax,%fs
movl %eax,%gs
+ movl pa(stack_start),%ecx
+ movl %eax,%ss
+ leal -__PAGE_OFFSET(%ecx),%esp
#endif /* CONFIG_SMP */
default_entry:

@@ -671,7 +681,7 @@ ENTRY(initial_page_table)

.data
ENTRY(stack_start)
- .long init_thread_union+THREAD_SIZE
+ .long initial_stack_pointer
.long __BOOT_DS

ready: .byte 0
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