Messages in this thread | | | Date | Fri, 25 Apr 2014 14:20:29 -0700 | From | "H. Peter Anvin" <> | Subject | Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE* |
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On 04/25/2014 05:02 AM, Pavel Machek wrote: > > Just to understand the consequences -- we leak 16 bit of kernel data > to the userspace, right? Because it is %esp, we know that we leak > stack address, which is not too sensitive, but will make kernel > address randomization less useful...? >
It is rather sensitive, in fact.
>> The 64-bit implementation works like this: >> >> Set up a ministack for each CPU, which is then mapped 65536 times >> using the page tables. This implementation uses the second-to-last >> PGD slot for this; with a 64-byte espfix stack this is sufficient for >> 2^18 CPUs (currently we support a max of 2^13 CPUs.) > > 16-bit stack segments on 64-bit machine. Who still uses it? Dosemu? > Wine? Would the solution be to disallow that?
Welcome to the show. We do, in fact disallow it now in the 3.15-rc series. The Wine guys are complaining.
-hpa
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