[PATCH]x86_64 debug_stack nested patch (again)

[PATCH]x86_64 debug_stack nested patch (again)

[bibo,mao]

Hi,
In x86_64 platform, INT1 and INT3 trap stack is IST stack called DEBUG_STACK,
when INT1/INT3 trap happens, system will switch to DEBUG_STACK by hardware. 
Current DEBUG_STACK size is 4K, when int1/int3 trap happens, kernel will 
minus current DEBUG_STACK IST value by 4k. But if int3/int1 trap is nested, 
it will destroy other vector's IST stack. This patch modifies this, it sets 
DEBUG_STACK size as 8K and allows two level of nested int1/int3 trap.

Kprobe DEBUG_STACK may be nested, because kprobe hanlder may be probed 
by other kprobes. This patch is against 2.6.17-rc3. Thanks jbeulich for pointing out error in the first patch.

Signed-Off-By: bibo, mao <bibo.mao@intel.com>

--- 2.6.17-rc3.org/include/asm-x86_64/page.h	2006-05-10 12:07:18.000000000 +0800
+++ 2.6.17-rc3/include/asm-x86_64/page.h	2006-05-10 12:19:24.000000000 +0800
@@ -20,7 +20,7 @@
 #define EXCEPTION_STACK_ORDER 0
 #define EXCEPTION_STKSZ (PAGE_SIZE << EXCEPTION_STACK_ORDER)
 
-#define DEBUG_STACK_ORDER EXCEPTION_STACK_ORDER
+#define DEBUG_STACK_ORDER (EXCEPTION_STACK_ORDER + 1)
 #define DEBUG_STKSZ (PAGE_SIZE << DEBUG_STACK_ORDER)
 
 #define IRQSTACK_ORDER 2


Thanks
bibo,mao

Re: [PATCH]x86_64 debug_stack nested patch (again)

[Andrew Morton]

"bibo,mao" <bibo.mao@intel.com> wrote:
>
> Hi,
> In x86_64 platform, INT1 and INT3 trap stack is IST stack called DEBUG_STACK,
> when INT1/INT3 trap happens, system will switch to DEBUG_STACK by hardware. 
> Current DEBUG_STACK size is 4K, when int1/int3 trap happens, kernel will 
> minus current DEBUG_STACK IST value by 4k. But if int3/int1 trap is nested, 
> it will destroy other vector's IST stack. This patch modifies this, it sets 
> DEBUG_STACK size as 8K and allows two level of nested int1/int3 trap.
> 
> Kprobe DEBUG_STACK may be nested, because kprobe hanlder may be probed 
> by other kprobes. This patch is against 2.6.17-rc3. Thanks jbeulich for pointing out error in the first patch.
> 
> Signed-Off-By: bibo, mao <bibo.mao@intel.com>
> 
> --- 2.6.17-rc3.org/include/asm-x86_64/page.h	2006-05-10 12:07:18.000000000 +0800
> +++ 2.6.17-rc3/include/asm-x86_64/page.h	2006-05-10 12:19:24.000000000 +0800
> @@ -20,7 +20,7 @@
>  #define EXCEPTION_STACK_ORDER 0
>  #define EXCEPTION_STKSZ (PAGE_SIZE << EXCEPTION_STACK_ORDER)
>  
> -#define DEBUG_STACK_ORDER EXCEPTION_STACK_ORDER
> +#define DEBUG_STACK_ORDER (EXCEPTION_STACK_ORDER + 1)
>  #define DEBUG_STKSZ (PAGE_SIZE << DEBUG_STACK_ORDER)
>  
>  #define IRQSTACK_ORDER 2

So....   why not do it this way?



--- devel/include/asm-x86_64/page.h~x86_64-kprobes-debug_stack-nesting-fix	2006-05-11 04:15:12.000000000 -0700
+++ devel-akpm/include/asm-x86_64/page.h	2006-05-11 04:16:07.000000000 -0700
@@ -20,7 +20,15 @@
 #define EXCEPTION_STACK_ORDER 0
 #define EXCEPTION_STKSZ (PAGE_SIZE << EXCEPTION_STACK_ORDER)
 
+#ifdef CONFIG_KPROBES
+/*
+ * kprobes uses an 8k stack because int1/int3 exceptions can nest
+ */
+#define DEBUG_STACK_ORDER (EXCEPTION_STACK_ORDER + 1)
+#else
 #define DEBUG_STACK_ORDER EXCEPTION_STACK_ORDER
+#endif
+
 #define DEBUG_STKSZ (PAGE_SIZE << DEBUG_STACK_ORDER)
 
 #define IRQSTACK_ORDER 2
_

Re: [PATCH]x86_64 debug_stack nested patch (again)

[Andi Kleen]

On Thursday 11 May 2006 13:17, Andrew Morton wrote:
> "bibo,mao" <bibo.mao@intel.com> wrote:
> >
> > Hi,
> > In x86_64 platform, INT1 and INT3 trap stack is IST stack called DEBUG_STACK,
> > when INT1/INT3 trap happens, system will switch to DEBUG_STACK by hardware. 
> > Current DEBUG_STACK size is 4K, when int1/int3 trap happens, kernel will 
> > minus current DEBUG_STACK IST value by 4k. But if int3/int1 trap is nested, 
> > it will destroy other vector's IST stack. This patch modifies this, it sets 
> > DEBUG_STACK size as 8K and allows two level of nested int1/int3 trap.
> > 
> > Kprobe DEBUG_STACK may be nested, because kprobe hanlder may be probed 
> > by other kprobes. This patch is against 2.6.17-rc3. Thanks jbeulich for pointing out error in the first patch.
> > 
> > Signed-Off-By: bibo, mao <bibo.mao@intel.com>
> > 
> > --- 2.6.17-rc3.org/include/asm-x86_64/page.h	2006-05-10 12:07:18.000000000 +0800
> > +++ 2.6.17-rc3/include/asm-x86_64/page.h	2006-05-10 12:19:24.000000000 +0800
> > @@ -20,7 +20,7 @@
> >  #define EXCEPTION_STACK_ORDER 0
> >  #define EXCEPTION_STKSZ (PAGE_SIZE << EXCEPTION_STACK_ORDER)
> >  
> > -#define DEBUG_STACK_ORDER EXCEPTION_STACK_ORDER
> > +#define DEBUG_STACK_ORDER (EXCEPTION_STACK_ORDER + 1)
> >  #define DEBUG_STKSZ (PAGE_SIZE << DEBUG_STACK_ORDER)
> >  
> >  #define IRQSTACK_ORDER 2
> 
> So....   why not do it this way?

Last time we discussed this I was told it could nest upto 3 or 4 times
So that still wouldn't work.

If anything they should decrease the int3/debug stack to 2K, then 8K 
might be enough.

Or even better would be to fix kprobes to not do that.

I think paranoidentry would need to be fixed for that too.

-Andi

Re: [PATCH]x86_64 debug_stack nested patch (again)

[bibo,mao]

Sorry for late reply, interrupt is disabled when int3/int1 trap happens 
and NMI is not permitted for kprobe in x86_64 platform,nest level of kprobe 
is 2 at most. So that will work well if DEBUG_STACK is set to 8K when CONFIG_KPROBE
option is set.

Thanks
bibo,mao

Andi Kleen wrote:
> On Thursday 11 May 2006 13:17, Andrew Morton wrote:
>> "bibo,mao" <bibo.mao@intel.com> wrote:
>>> Hi,
>>> In x86_64 platform, INT1 and INT3 trap stack is IST stack called DEBUG_STACK,
>>> when INT1/INT3 trap happens, system will switch to DEBUG_STACK by hardware. 
>>> Current DEBUG_STACK size is 4K, when int1/int3 trap happens, kernel will 
>>> minus current DEBUG_STACK IST value by 4k. But if int3/int1 trap is nested, 
>>> it will destroy other vector's IST stack. This patch modifies this, it sets 
>>> DEBUG_STACK size as 8K and allows two level of nested int1/int3 trap.
>>>
>>> Kprobe DEBUG_STACK may be nested, because kprobe hanlder may be probed 
>>> by other kprobes. This patch is against 2.6.17-rc3. Thanks jbeulich for pointing out error in the first patch.
>>>
>>> Signed-Off-By: bibo, mao <bibo.mao@intel.com>
>>>
>>> --- 2.6.17-rc3.org/include/asm-x86_64/page.h	2006-05-10 12:07:18.000000000 +0800
>>> +++ 2.6.17-rc3/include/asm-x86_64/page.h	2006-05-10 12:19:24.000000000 +0800
>>> @@ -20,7 +20,7 @@
>>>  #define EXCEPTION_STACK_ORDER 0
>>>  #define EXCEPTION_STKSZ (PAGE_SIZE << EXCEPTION_STACK_ORDER)
>>>  
>>> -#define DEBUG_STACK_ORDER EXCEPTION_STACK_ORDER
>>> +#define DEBUG_STACK_ORDER (EXCEPTION_STACK_ORDER + 1)
>>>  #define DEBUG_STKSZ (PAGE_SIZE << DEBUG_STACK_ORDER)
>>>  
>>>  #define IRQSTACK_ORDER 2
>> So....   why not do it this way?
> 
> Last time we discussed this I was told it could nest upto 3 or 4 times
> So that still wouldn't work.
> 
> If anything they should decrease the int3/debug stack to 2K, then 8K 
> might be enough.
> 
> Or even better would be to fix kprobes to not do that.
> 
> I think paranoidentry would need to be fixed for that too.
> 
> -Andi
> 
> -
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