From: Peter Collingbourne <pcc@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Dave Martin <Dave.Martin@arm.com>, Will Deacon <will@kernel.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Alistair Delva <adelva@google.com>,
Lokesh Gidra <lokeshgidra@google.com>,
William McVicker <willmcvicker@google.com>,
Evgenii Stepanov <eugenis@google.com>,
Mitch Phillips <mitchp@google.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Linux Memory Management List <linux-mm@kvack.org>
Subject: Re: [PATCH] userfaultfd: preserve user-supplied address tag in struct uffd_msg
Date: Wed, 30 Jun 2021 16:29:38 -0700 [thread overview]
Message-ID: <CAMn1gO5sZPtBFM+E=2y58i6H7YXcMQqQW1OE_u4F_JwUjLn_2w@mail.gmail.com> (raw)
In-Reply-To: <20210630160831.cf30a5cfa1df524aed42f3bd@linux-foundation.org>
On Wed, Jun 30, 2021 at 4:08 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Mon, 28 Jun 2021 18:20:10 -0700 Peter Collingbourne <pcc@google.com> wrote:
>
> > If a user program uses userfaultfd on ranges of heap memory, it may
> > end up passing a tagged pointer to the kernel in the range.start
> > field of the UFFDIO_REGISTER ioctl. This can happen when using an
> > MTE-capable allocator, or on Android if using the Tagged Pointers
> > feature for MTE readiness [1].
> >
> > When a fault subsequently occurs, the tag is stripped from the fault
> > address returned to the application in the fault.address field
> > of struct uffd_msg. However, from the application's perspective,
> > the tagged address *is* the memory address, so if the application
> > is unaware of memory tags, it may get confused by receiving an
> > address that is, from its point of view, outside of the bounds of the
> > allocation. We observed this behavior in the kselftest for userfaultfd
> > [2] but other applications could have the same problem.
> >
> > Fix this by remembering which tag was used to originally register the
> > userfaultfd and passing that tag back in fault.address. In a future
> > enhancement, we may want to pass back the original fault address,
> > but like SA_EXPOSE_TAGBITS, this should be guarded by a flag.
>
> Do we have a Fixes: for this?
>
> Is a -stable backport warranted?
Good point. I think this was an oversight in the original tagged
address ABI, so the appropriate Fixes would be the one that introduced
the prctl(). A stable backport seems reasonable, that's what we're
planning to do in our Android kernel branch anyway. Added the tags in
v2.
Peter
WARNING: multiple messages have this Message-ID (diff)
From: Peter Collingbourne <pcc@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Dave Martin <Dave.Martin@arm.com>, Will Deacon <will@kernel.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Alistair Delva <adelva@google.com>,
Lokesh Gidra <lokeshgidra@google.com>,
William McVicker <willmcvicker@google.com>,
Evgenii Stepanov <eugenis@google.com>,
Mitch Phillips <mitchp@google.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Linux Memory Management List <linux-mm@kvack.org>
Subject: Re: [PATCH] userfaultfd: preserve user-supplied address tag in struct uffd_msg
Date: Wed, 30 Jun 2021 16:29:38 -0700 [thread overview]
Message-ID: <CAMn1gO5sZPtBFM+E=2y58i6H7YXcMQqQW1OE_u4F_JwUjLn_2w@mail.gmail.com> (raw)
In-Reply-To: <20210630160831.cf30a5cfa1df524aed42f3bd@linux-foundation.org>
On Wed, Jun 30, 2021 at 4:08 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Mon, 28 Jun 2021 18:20:10 -0700 Peter Collingbourne <pcc@google.com> wrote:
>
> > If a user program uses userfaultfd on ranges of heap memory, it may
> > end up passing a tagged pointer to the kernel in the range.start
> > field of the UFFDIO_REGISTER ioctl. This can happen when using an
> > MTE-capable allocator, or on Android if using the Tagged Pointers
> > feature for MTE readiness [1].
> >
> > When a fault subsequently occurs, the tag is stripped from the fault
> > address returned to the application in the fault.address field
> > of struct uffd_msg. However, from the application's perspective,
> > the tagged address *is* the memory address, so if the application
> > is unaware of memory tags, it may get confused by receiving an
> > address that is, from its point of view, outside of the bounds of the
> > allocation. We observed this behavior in the kselftest for userfaultfd
> > [2] but other applications could have the same problem.
> >
> > Fix this by remembering which tag was used to originally register the
> > userfaultfd and passing that tag back in fault.address. In a future
> > enhancement, we may want to pass back the original fault address,
> > but like SA_EXPOSE_TAGBITS, this should be guarded by a flag.
>
> Do we have a Fixes: for this?
>
> Is a -stable backport warranted?
Good point. I think this was an oversight in the original tagged
address ABI, so the appropriate Fixes would be the one that introduced
the prctl(). A stable backport seems reasonable, that's what we're
planning to do in our Android kernel branch anyway. Added the tags in
v2.
Peter
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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-06-30 23:29 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-29 1:20 [PATCH] userfaultfd: preserve user-supplied address tag in struct uffd_msg Peter Collingbourne
2021-06-29 1:20 ` Peter Collingbourne
2021-06-30 23:08 ` Andrew Morton
2021-06-30 23:08 ` Andrew Morton
2021-06-30 23:29 ` Peter Collingbourne [this message]
2021-06-30 23:29 ` Peter Collingbourne
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