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From: Marc Zyngier <maz@kernel.org>
To: wangrongwei <rongwei.wang@linux.alibaba.com>
Cc: vkoul@kernel.org, gshan@redhat.com, Anson.Huang@nxp.com,
	geert+renesas@glider.be, catalin.marinas@arm.com,
	masahiroy@kernel.org, linux-kernel@vger.kernel.org,
	krzk@kernel.org, bjorn.andersson@linaro.org, michael@walle.cc,
	olof@lixom.net, shawnguo@kernel.org, vincenzo.frascino@arm.com,
	Will Deacon <will@kernel.org>,
	ardb@kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 0/3] arm64:msr: Add MSR driver
Date: Tue, 01 Dec 2020 15:37:26 +0000	[thread overview]
Message-ID: <7e9ae04f3394a85aa3b8fe8947a44009@kernel.org> (raw)
In-Reply-To: <6FA68A07-F718-46F5-81B4-586A5ED3E479@linux.alibaba.com>

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

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

_______________________________________________
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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org>
To: wangrongwei <rongwei.wang@linux.alibaba.com>
Cc: catalin.marinas@arm.com, Will Deacon <will@kernel.org>,
	bjorn.andersson@linaro.org, shawnguo@kernel.org,
	gshan@redhat.com, geert+renesas@glider.be, Anson.Huang@nxp.com,
	masahiroy@kernel.org, michael@walle.cc, krzk@kernel.org,
	linux-kernel@vger.kernel.org, vkoul@kernel.org, olof@lixom.net,
	vincenzo.frascino@arm.com, ardb@kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 0/3] arm64:msr: Add MSR driver
Date: Tue, 01 Dec 2020 15:37:26 +0000	[thread overview]
Message-ID: <7e9ae04f3394a85aa3b8fe8947a44009@kernel.org> (raw)
In-Reply-To: <6FA68A07-F718-46F5-81B4-586A5ED3E479@linux.alibaba.com>

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

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

  reply	other threads:[~2020-12-01 15:47 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-30 17:48 [PATCH 0/3] arm64:msr: Add MSR driver Rongwei Wang
2020-11-30 17:48 ` Rongwei Wang
2020-11-30 17:48 ` [PATCH 1/3] arm64:insn: Export symbols for MSR ARM driver Rongwei Wang
2020-11-30 17:48   ` Rongwei Wang
2020-11-30 17:48 ` [PATCH 2/3] arm64:msr: Introduce " Rongwei Wang
2020-11-30 17:48   ` Rongwei Wang
2020-11-30 23:14   ` kernel test robot
2020-11-30 17:48 ` [PATCH 3/3] arm64:msr: Enable " Rongwei Wang
2020-11-30 17:48   ` Rongwei Wang
2020-11-30 17:57 ` [PATCH 0/3] arm64:msr: Add MSR driver Will Deacon
2020-11-30 17:57   ` Will Deacon
2020-12-01  2:55   ` wangrongwei
2020-12-01  2:55     ` wangrongwei
2020-12-01  5:44   ` wangrongwei
2020-12-01  5:44     ` wangrongwei
2020-11-30 18:05 ` Marc Zyngier
2020-11-30 18:05   ` Marc Zyngier
2020-11-30 18:20   ` Randy Dunlap
2020-11-30 18:20     ` Randy Dunlap
2020-12-01  3:09   ` wangrongwei
2020-12-01  3:09     ` wangrongwei
2020-12-01  8:12     ` Marc Zyngier
2020-12-01  8:12       ` Marc Zyngier
2020-12-01 14:25       ` wangrongwei
2020-12-01 14:25         ` wangrongwei
2020-12-01 15:37         ` Marc Zyngier [this message]
2020-12-01 15:37           ` Marc Zyngier
2020-12-03  5:45           ` Rongwei Wang
2020-12-03  5:45             ` Rongwei Wang
2020-12-03  8:35             ` Marc Zyngier
2020-12-03  8:35               ` Marc Zyngier
2020-12-03 11:25               ` Rongwei Wang
2020-12-03 11:25                 ` Rongwei Wang
2020-12-03 11:45                 ` Marc Zyngier
2020-12-03 11:45                   ` Marc Zyngier
2020-12-03 12:22                   ` Rongwei Wang
2020-12-03 12:22                     ` Rongwei Wang
2020-12-03 11:50                 ` Mark Rutland
2020-12-03 11:50                   ` Mark Rutland
2020-11-30 19:03 ` Borislav Petkov
2020-11-30 19:03   ` Borislav Petkov
2020-12-01  3:44   ` wangrongwei
2020-12-01  3:44     ` wangrongwei
2020-12-01 11:26     ` Borislav Petkov
2020-12-01 11:26       ` Borislav Petkov
2020-12-01 14:33       ` wangrongwei
2020-12-01 14:33         ` wangrongwei
2020-12-01 14:54         ` Borislav Petkov
2020-12-01 14:54           ` Borislav Petkov
2020-12-01 15:17           ` Rongwei Wang
2020-12-01 15:17             ` Rongwei Wang
2020-12-01 15:25             ` Borislav Petkov
2020-12-01 15:25               ` Borislav Petkov
2020-12-03  2:09               ` Rongwei Wang
2020-12-03  2:09                 ` Rongwei Wang
2020-12-01 15:26             ` Ard Biesheuvel
2020-12-01 15:26               ` Ard Biesheuvel

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