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Date:   Tue, 03 Oct 2023 14:53:17 -0700
From:   "H. Peter Anvin" <hpa@zytor.com>
To:     Dave Hansen <dave.hansen@intel.com>, Ingo Molnar <mingo@kernel.org>
CC:     Alexey Dobriyan <adobriyan@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86_64: test that userspace stack is in fact NX
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On October 3, 2023 1:46:20 PM PDT, Dave Hansen <dave=2Ehansen@intel=2Ecom> =
wrote:
>On 10/3/23 12:30, Ingo Molnar wrote:
>> * Ingo Molnar <mingo@kernel=2Eorg> 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=2E
>> BTW=2E, it's also questionable whether the owner is *aware* of the fact=
 that=20
>> NX is not available: what if some kernel debug option cleared the NX fl=
ag,=20
>> unintended, or there's some serious firmware bug?
>>=20
>> However unlikely those situations might be, I think unconditionally war=
ning=20
>> about NX not available is a very 2023 thing to do=2E
>
>100% agree for x86_64=2E  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=2E
>
>For 32-bit, the situation is reversed=2E  The majority of 32-bit-only CPU=
s
>never had NX=2E  The only reason to even *do* this check on 32-bit is tha=
t
>we think folks are running i386 kernels on x86_64 hardware _or_ we just
>don't care about 32-bit in the first place=2E
>
>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=2E  But I honestly don't care
>that much=2E  I wouldn't NAK (or not merge) this patch over it=2E

Perhaps we should also complain at people who are still running 32-bit ker=
nels on 64-bit hardware? It has been 20 years=2E=2E=2E