Re: [Xen-devel] [PATCH v3 09/17] livepatch/arm[32, 64]: Modify livepatch_funcs

[Julien Grall <julien.grall@xxxxxxx>]

Hi Konrad,

On 19/09/17 01:35, Konrad Rzeszutek Wilk wrote:
> On Thu, Sep 14, 2017 at 02:20:42PM +0100, Julien Grall wrote:
> > Hi Konrad,
> >
> > On 12/09/17 01:37, Konrad Rzeszutek Wilk wrote:
> > > This was found when porting livepatch-build-tools to ARM64/32.
> > >
> > > When livepatch-build-tools are built (and test-case thanks to:
> > > livepatch/tests: Make sure all .livepatch.funcs sections are read-only)
> > > the .livepatch.funcs are in read-only section.
> > >
> > > However the hypervisor uses the 'opaque' for its own purpose, that
> > > is stashing the original code. But the .livepatch_funcs section is
> > > in the RO vmap area so on ARM[32,64] we get a fault.
> > This is because the payload is secure at loading and therefore before it get
> > applied, right?
> Yes.
> > I was wondering if we could either defer the call to secure_payload or make
> > the region temporarily writeable?
> This patch creates a temporary writeable virtual address space.
>
> But the idea of making the region temporarily writeable is also possible.
> Is there a specific register I can use for this?
There is no specific register. I was suggest to call modify_xen_mappings 
on the region with (RW) and then you are done switch back to RO/RX.
I can't see any implication on Arm to temporary switch a mapping from
read-only to read-write. I am not sure for x86.

Cheers,

--
Julien Grall

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