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From: Ard Biesheuvel <ardb@kernel.org>
To: Kees Cook <keescook@chromium.org>
Cc: Guenter Roeck <linux@roeck-us.net>,
	Peter Zijlstra <peterz@infradead.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	linux-kernel@vger.kernel.org, Darren Hart <dvhart@infradead.org>,
	Andy Shevchenko <andy@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, linux-efi@vger.kernel.org,
	"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH] x86/mm+efi: Avoid creating W+X mappings
Date: Fri, 23 Sep 2022 21:53:02 +0200	[thread overview]
Message-ID: <CAMj1kXHckEg6rwBSEc6piu=-JZzyDh7j+pvGSFp1OBUQuofrEQ@mail.gmail.com> (raw)
In-Reply-To: <202209231126.6855D54@keescook>

On Fri, 23 Sept 2022 at 20:31, Kees Cook <keescook@chromium.org> wrote:
>
> On Fri, Sep 23, 2022 at 04:26:58PM +0200, Ard Biesheuvel wrote:
> > I was basically making the point that we still support i386 without
> > PAE (which is a prerequisite for supporting non-executable mappings),
> > and if we are going to be pedantic about security on this
> > architecture, we should probably make PAE mandatory as well.
>
> My expectation would be that if someone is running modern kernels on i386,
> they're not using PAE. If they care about PAE, I'd expect them to have
> long since moved to x86_64.
>

Not sure I follow. If they care about PAE, they turn it on. Or do you
mean 'if they care about being able to address lots of physical
memory'? Because the *other* reason you might care about PAE is
because it gives you NX support.

But currently, PAE is not even enabled in the i386_defconfig, and
defaults to off. This means people that are unaware of this won't
enable it, and will be running without NX support.

> > If we are ok with the current state, enabling this permission check on
> > i386 makes no sense.
>
> I'd agree. If it's a choice between "spend a lot of time making sure
> this works correctly on i386" and "don't do this at all on i386", I
> would pick the latter. If someone steps up to do the former, then by
> all means take the patches.
>

OK, so it seems we're all in violent agreement here. And if there is
ever a push for enabling security features on 32-bit, we can add this
to the laundry list of things that need to be looked at.

  reply	other threads:[~2022-09-23 19:53 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <08906193-246b-c874-8bac-1d98d2313ac4@roeck-us.net>
2022-09-22 19:31 ` [PATCH] x86/mm+efi: Avoid creating W+X mappings Dave Hansen
2022-09-22 22:08   ` Ard Biesheuvel
2022-09-23  6:59     ` Peter Zijlstra
2022-09-23  9:49       ` Ard Biesheuvel
2022-09-23 13:58         ` Guenter Roeck
2022-09-23 14:26           ` Ard Biesheuvel
2022-09-23 18:31             ` Kees Cook
2022-09-23 19:53               ` Ard Biesheuvel [this message]
2022-09-23 21:19                 ` Kees Cook
2022-09-23 22:15                   ` Dave Hansen
2022-09-23 22:32                     ` Eric W. Biederman
2022-09-24  0:04                     ` Kees Cook

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