linux-kernel - Re: [PATCH] x86_64: test that userspace stack is in fact NX

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Date:   Tue, 03 Oct 2023 14:53:17 -0700
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Dave Hansen <dave.hansen@...el.com>, Ingo Molnar <mingo@...nel.org>
CC:     Alexey Dobriyan <adobriyan@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86_64: test that userspace stack is in fact NX

On October 3, 2023 1:46:20 PM PDT, Dave Hansen <dave.hansen@...el.com> wrote:
>On 10/3/23 12:30, Ingo Molnar wrote:
>> * Ingo Molnar <mingo@...nel.org> wrote:
>>> Because not having NX in 2023 on any system that is threatened is a
>>> big security vulnerability in itself, and whether the vendor or owner
>>> intentionally did that or not doesn't really matter, and a failing
>>> kernel testcase will be the least of their problems.
>> BTW., it's also questionable whether the owner is *aware* of the fact that 
>> NX is not available: what if some kernel debug option cleared the NX flag, 
>> unintended, or there's some serious firmware bug?
>> 
>> However unlikely those situations might be, I think unconditionally warning 
>> about NX not available is a very 2023 thing to do.
>
>100% agree for x86_64.  Any sane x86_64 system has NX and the rest are
>noise that can live with the error message, unless someone shows up with
>a compelling reason why not.
>
>For 32-bit, the situation is reversed.  The majority of 32-bit-only CPUs
>never had NX.  The only reason to even *do* this check on 32-bit is that
>we think folks are running i386 kernels on x86_64 hardware _or_ we just
>don't care about 32-bit in the first place.
>
>In the end, I think if we're going to do this test on i386, we should
>_also_ do the 5-lines-of-code CPUID check.  But I honestly don't care
>that much.  I wouldn't NAK (or not merge) this patch over it.

Perhaps we should also complain at people who are still running 32-bit kernels on 64-bit hardware? It has been 20 years...