linux-kernel - Re: [PATCH 1/2] PCI/MSI: Cache the MSIX table size

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <87pmb4p0ik.fsf@ubik.fi.intel.com>
Date:   Tue, 24 Jan 2023 14:42:11 +0200
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Marc Zyngier <maz@...nel.org>, darwi@...utronix.de,
        elena.reshetova@...el.com, kirill.shutemov@...ux.intel.com,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        stable@...r.kernel.org, alexander.shishkin@...ux.intel.com
Subject: Re: [PATCH 1/2] PCI/MSI: Cache the MSIX table size

Leon Romanovsky <leon@...nel.org> writes:

> On Tue, Jan 24, 2023 at 01:52:37PM +0200, Alexander Shishkin wrote:
>> Leon Romanovsky <leon@...nel.org> writes:
>> 
>> > I'm not security expert here, but not sure that this protects from anything.
>> > 1. Kernel relies on working and not-malicious HW. There are gazillion ways
>> > to cause crashes other than changing MSI-X.
>> 
>> This particular bug was preventing our fuzzing from going deeper into
>> the code and reaching some more of the aforementioned gazillion bugs.
>
> Your commit message says nothing about fuzzing, but talks about
> malicious device. 

A malicious device is what the fuzzing is aiming to simulate. The fact
of fuzzing process itself didn't seem relevant to the patch, so I didn't
include it, going instead for the problem statement and proposed
solution. Will the commit message benefit from mentioning fuzzing?

> Do you see "gazillion bugs" for devices which don't change their MSI-X
> table size under the hood, which is main kernel assumption?

Not so far.

> If yes, you should fix these bugs.

That's absolutely the intention.

>> > 2. Device can report large table size, kernel will cache it and
>> > malicious device will reduce it back. It is not handled and will cause
>> > to kernel crash too.
>> 
>> How would that happen? If the device decides to have fewer vectors,
>> they'll all still fit in the ioremapped MSIX table. The worst thing that
>> can happen is 0xffffffff reads from the mmio space, which a device can
>> do anyway. But that shouldn't trigger a page fault or otherwise
>> crash. Or am I missing something?
>
> Like I said, I'm no expert. You should tell me if it safe for all
> callers of pci_msix_vec_count().

Well, since you stated that the reverse will cause a kernel crash, I had
to ask how. I'll include some version of the above paragraph in the
commit message to indicate that we reverse situation has been considered.

Regards,
--
Alex