From: Andy Lutomirski <luto@amacapital.net>
To: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Borislav Petkov <bp@alien8.de>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Ingo Molnar <mingo@kernel.org>,
Stephen Smalley <sds@tycho.nsa.gov>,
"x86@kernel.org" <x86@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Kees Cook <keescook@chromium.org>,
Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Andy Lutomirski <luto@kernel.org>,
Denys Vlasenko <dvlasenk@redhat.com>,
Brian Gerst <brgerst@gmail.com>,
"linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>
Subject: Re: [PATCH v2] x86/mm: warn on W+x mappings
Date: Wed, 21 Oct 2015 13:49:07 -0700 [thread overview]
Message-ID: <CALCETrX=ddvegyK2_cvwHW=mXb3c8mGpfRT5WFP+qW_=nm_D-A@mail.gmail.com> (raw)
In-Reply-To: <20151021204522.GB20338@codeblueprint.co.uk>
On Wed, Oct 21, 2015 at 1:45 PM, Matt Fleming <matt@codeblueprint.co.uk> wrote:
> On Wed, 21 Oct, at 11:46:53AM, Andy Lutomirski wrote:
>>
>> If the UEFI stuff is mapped in its own PGD entry, we could just RO
>> that entire PGD entry everywhere except the UEFI pgd (and make sure to
>> clear G so that the TLB entries get zapped).
>
> What would be the benefit of making it RO as opposed to not having it
> mapped at all?
Nothing.
> The mappings only exist in the trampoline_pgd right now
> for x86 which minimizes the potentially vulnerable code paths to the
> EFI runtime calls and the suspend/resume code.
Oh, I didn't realize it.
So what's the problem here? Honestly, while UEFI is full of
questionable things, I don't really see how an unprivileged user
program should be able to cause malicious input to be send to UEFI
code, so it should be quite difficult to exploit a buffer overflow or
other errant write in UEFI to escalate privileges from user to
anything else. (Kernel -> SMM escalation is a whole different story,
but preventing that is SMM's business, not the kernel's. I've
actually been a wee bit tempted to write a /dev/smram driver to expose
SMRAM using a portfolio of old known exploits.)
--Andy
--
Andy Lutomirski
AMA Capital Management, LLC
next prev parent reply other threads:[~2015-10-21 20:49 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-02 19:29 [PATCH v2] x86/mm: warn on W+x mappings Stephen Smalley
2015-10-02 20:44 ` Kees Cook
2015-10-03 11:27 ` Ingo Molnar
2015-10-05 19:13 ` Stephen Smalley
2015-10-06 7:32 ` Ingo Molnar
2015-10-06 15:37 ` Stephen Smalley
2015-10-12 11:36 ` Borislav Petkov
2015-10-12 12:41 ` Matt Fleming
2015-10-12 12:49 ` Ingo Molnar
2015-10-12 12:55 ` Matt Fleming
2015-10-12 14:17 ` Ingo Molnar
2015-10-12 14:49 ` Matt Fleming
2015-10-12 15:34 ` Ard Biesheuvel
2015-10-12 15:50 ` Matt Fleming
2015-10-12 16:43 ` Ard Biesheuvel
2015-10-14 15:18 ` Ingo Molnar
2015-10-14 15:30 ` Andy Lutomirski
2015-10-14 15:35 ` Borislav Petkov
2015-10-15 10:10 ` Matt Fleming
2015-10-15 10:33 ` Borislav Petkov
2015-10-16 1:45 ` Ricardo Neri
2015-10-14 21:02 ` Matt Fleming
2015-10-21 9:42 ` Ingo Molnar
2015-10-21 12:49 ` Ingo Molnar
2015-10-21 12:57 ` Ard Biesheuvel
2015-10-21 13:24 ` Borislav Petkov
2015-10-21 13:28 ` Ard Biesheuvel
2015-10-21 14:36 ` Borislav Petkov
2015-10-21 18:46 ` Andy Lutomirski
2015-10-21 20:45 ` Matt Fleming
2015-10-21 20:49 ` Andy Lutomirski [this message]
2015-10-21 20:38 ` Matt Fleming
2015-10-12 14:56 ` Josh Triplett
2015-10-14 15:19 ` Ingo Molnar
2015-10-14 16:47 ` Josh Triplett
2015-10-21 9:43 ` Ingo Molnar
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