Re: [PATCH v2 2/3] MIPS: Setup an instruction emulation in VDSO protected page instead of user stack

[Leonid Yegoshin]

On 10/10/2014 03:03 AM, James Hogan wrote:
> I just mean an (illegal/undefined) sequence of FPU branch instructions 
> in one anothers delay slots shouldn't be able to crash the kernel. 
> Actually 2 of them would be enough to verify the kernel didn't get too 
> confused. Maybe the second will be detected & ignored, or maybe it 
> doesn't matter if the first emuframe gets overwritten by the second 
> one from the kernels point of view.

Yes, I am looking into that sequences. I try to keep both emulators 
isolated from the rest of kernel and from each other as much as possible 
but intercalls via illegal combinations are still possible.


> From Peter Zijlstra:

> Right, look at uprobes, it does exactly all this with a single page.
> Slot allocation will block waiting for a free slot when all are in use.

I don't see a reason to change my 300 lines design into much more 
lengthy code. That code has more links to the rest of kernel and high 
possibility to execute atomic operation/locks/mutex/etc - I can't do it 
for emulation of MIPS locking instructions.

- Leonid.
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