From: Peter Zijlstra <peterz@infradead.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
linux-kernel@vger.kernel.org, Guenter Roeck <linux@roeck-us.net>,
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 08:59:53 +0200 [thread overview]
Message-ID: <Yy1ZadE6Vnnc2dNf@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAMj1kXHcF_iK_g0OZSkSv56Wmr=eQGQwNstcNjLEfS=mm7a06w@mail.gmail.com>
On Fri, Sep 23, 2022 at 12:08:57AM +0200, Ard Biesheuvel wrote:
> On Thu, 22 Sept 2022 at 21:32, Dave Hansen <dave.hansen@linux.intel.com> wrote:
> >
> > From: Peter Zijlstra <peterz@infradead.org>
> >
> > I'm planning on sticking this in x86/mm so that it goes upstream
> > along with the W+X detection code.
> >
> > --
> >
> > A recent x86/mm change warns and refuses to create W+X mappings.
> >
> > The 32-bit EFI code tries to create such a mapping and trips over
> > the new W+X refusal.
> >
> > Make the EFI_RUNTIME_SERVICES_CODE mapping read-only to fix it.
> >
>
> This is not safe. EFI_RUNTIME_SERVICES_CODE covers both .text and
> .data sections of the EFI runtime PE/COFF executables in memory, so
> you are essentially making .data and .bss read-only. (Whether those
> executables actually modify their .data and .bss at runtime is a
> different matter, but the point is that it used to be possible)
>
> More recent firmwares may provide a 'memory attributes table'
> separately which describes the individual sections, but older 32-bit
> firmwares are not even built with 4k section alignment, so code and
> data may share a single page. Note that we haven't wired up this
> memory attributes table on i386 at the moment, and I seriously doubt
> that 32-bit firmware in the field exposes it.
>
> Can we just turn off this feature for 32-bit?
Goodie; some seriously security minded people who did that EFI turd :/
Let's just heap it on the pile of 32bit sucks and should not be
considered a security target anymore and indeed kill this feature.
next prev parent reply other threads:[~2022-09-23 7:00 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 [this message]
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
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=Yy1ZadE6Vnnc2dNf@hirez.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=andy@infradead.org \
--cc=ardb@kernel.org \
--cc=bp@alien8.de \
--cc=dave.hansen@linux.intel.com \
--cc=dvhart@infradead.org \
--cc=hpa@zytor.com \
--cc=linux-efi@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@roeck-us.net \
--cc=mingo@redhat.com \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).