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SubjectRe: hv_hypercall_pg page permissios
On Tue, Apr 07, 2020 at 09:28:01AM +0200, Vitaly Kuznetsov wrote:
> Christoph Hellwig <hch@lst.de> writes:
>
> > Hi all,
> >
> > The x86 Hyper-V hypercall page (hv_hypercall_pg) is the only allocation
> > in the kernel using __vmalloc with exectutable persmissions, and the
> > only user of PAGE_KERNEL_RX. Is there any good reason it needs to
> > be readable? Otherwise we could use vmalloc_exec and kill off
> > PAGE_KERNEL_RX. Note that before 372b1e91343e6 ("drivers: hv: Turn off
> > write permission on the hypercall page") it was even mapped writable..
>
> [There is nothing secret in the hypercall page, by reading it you can
> figure out if you're running on Intel or AMD (VMCALL/VMMCALL) but it's
> likely not the only possible way :-)]
>
> I see no reason for hv_hypercall_pg to remain readable. I just
> smoke-tested

Thanks, I have the same in my WIP tree, but just wanted to confirm this
makes sense.

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