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

Marc Zyngier maz at kernel.org
Tue Dec 1 10:37:26 EST 2020

On 2020-12-01 14:25, wangrongwei wrote:
>> 2020年12月1日 下午4:12,Marc Zyngier <maz at kernel.org> 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.

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

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