Messages in this thread | | | Date | Fri, 4 Dec 2009 21:31:43 +0100 | From | Andi Kleen <> | Subject | Re: [PATCH] intel_txt: add s3 userspace memory integrity verification |
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> > Of course you would need to have a timeout before reset, and at this point the > > delay loops are not calibrated yet, so you don't know how to wait.
That was actually wrong, since you're coming back from S3 udelay should work. nm.
> > I would expect that early_printk() coupled with tboot's serial output would be sufficient for a case such as this. If we've done our work correctly, loss of integrity should only occur when the system is attacked across the S3 transition--which should be fairly rare and which should place a premium on prevention of the attacked code from executing. Esp. on servers, there may not be anyone to see console output anyway. Does early_printk() and a tboot reset seem like a reasonable approach?
At least classical vga/serial early_printk should be safe, I'm not sure about the early USB code recently added though, some auditing on that first would be good.
early_printk defaults to VGA text output, so if you do a reset you would need a delay first, otherwise noone can see it ever. But one could be done with udelay()
It'll be also invisible with frame buffer active, which is the common case for distributions. So basically in most cases the message would be invisible.
(not that panic is much better by default in this regard though, at least not without Jesse's recent frame buffer work ...)
-Andi
-- ak@linux.intel.com -- Speaking for myself only.
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