Re: [RFC 00/15] x86_64: Optimize percpu accesses

[Arjan van de Ven]

On Wed, 09 Jul 2008 13:00:19 -0700
ebiederm@xxxxxxxxxxxx (Eric W. Biederman) wrote:

> 
> I just took a quick look at how stack_protector works on x86_64.
> Unless there is some deep kernel magic that changes the segment
> register to %gs from the ABI specified %fs CC_STACKPROTECTOR is
> totally broken on x86_64.  We access our pda through %gs.

and so does gcc in kernel mode.

> 
> Further -fstack-protector-all only seems to detect against buffer
> overflows and thus corruption of the stack.  Not stack overflows.  So
> it doesn't appear especially useful.

stopping buffer overflows and other return address corruption is not
useful? Excuse me?

> 
> So we don't we kill the broken CONFIG_CC_STACKPROTECTOR.  Stop trying
> to figure out how to use a zero based percpu area.

So why don't we NOT do that and fix instead what you're trying to do?

> 
> That should allow us to make the current pda a per cpu variable, and
> use %gs with a large offset to access the per cpu area. 

and what does that gain us?


-- 
If you want to reach me at my work email, use arjan@xxxxxxxxxxxxxxx
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/