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Message-ID: <d76126be-9eda-d426-1fa5-a35fd4ca3d57@intel.com>
Date: Fri, 11 Aug 2023 16:42:26 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Jo Van Bulck <jo.vanbulck@...kuleuven.be>,
linux-kernel@...r.kernel.org, dave.hansen@...ux.intel.com,
luto@...nel.org, peterz@...radead.org, mingo@...hat.com,
sohil.mehta@...el.com
Cc: x86@...nel.org, bp@...en8.de, tglx@...utronix.de, hpa@...or.com
Subject: Re: [PATCH 1/1] x86/pti: Fix kernel warnings for pti= and nopti
cmdline options.
On 8/11/23 16:27, Jo Van Bulck wrote:
> On 11.08.23 14:36, Jo Van Bulck wrote:> static enum pti_mode {
>> PTI_AUTO = 0,
>> + PTI_FORCE_AUTO,
>> PTI_FORCE_OFF,
>> PTI_FORCE_ON
>> } pti_mode;
>
> I introduced a new PTI_FORCE_AUTO value here to make pti=auto override
> any mitigations=off parameter. However, I realize now that this may
> inadvertently affect other functions that test for pti_mode == PTI_AUTO
> (eg in pti_kernel_image_global_ok()).
>
> Having 2 constants PTI_AUTO and PTI_FORCE_AUTO is arguably not very
> neat, so we should better get rid of this. I see several options:
>
> - not have pti=auto override mitigations=off
> - have a global var to indicate pti= argument was passed
> - set pti_mode = PTI_AUTO in the pti_mode == PTI_FORCE_AUTO if branch
>
> Not sure which option would best match kernel coding guidelines?
This sound like it's getting a bit out of hand and reaching far beyond
cleaning up some (mostly) harmless warnings.
I bet we have a billion command-line parameters that conflict with each
other. mitigations=off and pti=auto is probably the least of our
worries. Nobody in their right mind is going to say, oh, I *only* want
PTI, I don't care about any other mitigations. That's nuts.
mitigations=off is the big hammer. If you set that, you're basically
shouting from the rooftops, "moar speed!!" You don't get security after
that.
pti=auto does *not* need to override mitigations=off.
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