From: Sean Christopherson <seanjc@google.com>
To: Tadeusz Struk <tadeusz.struk@linaro.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
kvm@vger.kernel.org, stable@vger.kernel.org,
syzbot+6cde2282daa792c49ab8@syzkaller.appspotmail.com
Subject: Re: [PATCH RESEND] KVM: x86/mmu: fix UAF in paging_update_accessed_dirty_bits
Date: Tue, 1 Feb 2022 01:11:32 +0000 [thread overview]
Message-ID: <YfiIxK36yD5pQgu3@google.com> (raw)
In-Reply-To: <YfB7KWFNMvo0FkCO@google.com>
On Tue, Jan 25, 2022, Sean Christopherson wrote:
> On Mon, Jan 24, 2022, Tadeusz Struk wrote:
> > On 1/24/22 10:29, Sean Christopherson wrote:
> > > On Mon, Jan 24, 2022, Paolo Bonzini wrote:
> > > > On 1/24/22 18:26, Tadeusz Struk wrote:
> > > > > Syzbot reported an use-after-free bug in update_accessed_dirty_bits().
> > > > > Fix this by checking if the memremap'ed pointer is still valid.
> > > > access_ok only checks that the pointer is in the userspace range. Is this
> > > > correct? And if so, what are the exact circumstances in which access_ok
> > > > returns a non-NULL but also non-userspace address?
> > > I "objected" to this patch in its initial posting[*]. AFAICT adding access_ok()
> > > is just masking a more egregious bug where interpretation of vm_pgoff as a PFN
> > > base is flat out wrong except for select backing stores that use VM_PFNMAP. In
> > > other words, the vm_pgoff hack works for the /dev/mem use case, but it is wrong
> > > in general.
> > >
> >
> > The issue here is not related to /dev/mem, but binder allocated memory, which is
> > yet another special mapping use case. In this case the condition
> >
> > if (!vma || !(vma->vm_flags & VM_PFNMAP))
> >
> > doesn't cover this special mappings. Adding the access_ok() was my something
> > that fixed the use-after-free issue for me, and since I didn't have anything
> > better I thought I will send an RFC to start some discussion.
> > After some more debugging I came up with the bellow.
> > Will that be more acceptable?
>
> I'm pretty sure anything that keeps the vm_pgoff "logic" is a band-aid. But I'm 99%
> sure we can simply do cmpxchg directly on the user address, we just need to get
> support for that, which has happily been posted[*]. I'll give that a shot tomorrow,
> I want to convert similar code in the emulator, it'd be very nice to purge all of
> this crud.
>
> [*] https://lore.kernel.org/all/20220120160822.852009966@infradead.org
Posted a series and belatedly realized my script didn't pick up Debugged-by: to Cc
you :-/ Let me know if you want me to forward any/all of the series to you.
https://lore.kernel.org/all/20220201010838.1494405-1-seanjc@google.com
next prev parent reply other threads:[~2022-02-01 1:11 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-24 17:26 [PATCH RESEND] KVM: x86/mmu: fix UAF in paging_update_accessed_dirty_bits Tadeusz Struk
2022-01-24 18:07 ` Paolo Bonzini
2022-01-24 18:29 ` Sean Christopherson
2022-01-24 21:02 ` Tadeusz Struk
2022-01-25 22:35 ` Sean Christopherson
2022-02-01 1:11 ` Sean Christopherson [this message]
2022-02-01 2:29 ` Tadeusz Struk
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=YfiIxK36yD5pQgu3@google.com \
--to=seanjc@google.com \
--cc=bp@alien8.de \
--cc=dave.hansen@linux.intel.com \
--cc=hpa@zytor.com \
--cc=jmattson@google.com \
--cc=joro@8bytes.org \
--cc=kvm@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=pbonzini@redhat.com \
--cc=stable@vger.kernel.org \
--cc=syzbot+6cde2282daa792c49ab8@syzkaller.appspotmail.com \
--cc=tadeusz.struk@linaro.org \
--cc=tglx@linutronix.de \
--cc=vkuznets@redhat.com \
--cc=wanpengli@tencent.com \
--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).