Re: [PATCH 0/3] arm64:msr: Add MSR driver

[Marc Zyngier]

On 2020-12-01 14:25, wangrongwei wrote:
> > 2020年12月1日 下午4:12，Marc Zyngier <maz@xxxxxxxxxx> 写道：
> >
> > On 2020-12-01 03:09, wangrongwei wrote:
> > > Hi
> > > We have validate this driver in vm and physical machine, and works 
> > > fine.
> >
> > But what does "work fine" mean? None of these system registers are 
> > supposed
> > to be accessible from userspace, so please explain *what* you are 
> > trying to
> > do with this, other that introducing security holes and general system
> > instability?
> I think I know what you mean. Do you want me to describe how we 
> achieved it?
> In x86, the different registers can be accessed directly using the
> rdmsr and wrmsr instructions, but in ARM, since these two instructions
> are missing, so we modify the code segment during runtime, similar to
> the principle of static_key.

[...]

These are implementation details, none of which answer my question:

What makes you think this is a good idea? I cannot see any legitimate
reason for userspace to ever access privileged system registers, and
the fact that x86 has such feature isn't a good justification.

        M.
--
Jazz is not dead. It just smells funny...