From: Catalin Marinas <catalin.marinas@arm.com>
To: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
Andrew Morton <akpm@linux-foundation.org>,
Will Deacon <will@kernel.org>, Dmitry Vyukov <dvyukov@google.com>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Alexander Potapenko <glider@google.com>,
Marco Elver <elver@google.com>,
Evgenii Stepanov <eugenis@google.com>,
Branislav Rankov <Branislav.Rankov@arm.com>,
Andrey Konovalov <andreyknvl@google.com>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Subject: Re: [PATCH v14 8/8] kselftest/arm64: Verify that TCO is enabled in load_unaligned_zeropad()
Date: Thu, 11 Mar 2021 16:28:21 +0000 [thread overview]
Message-ID: <20210311162820.GE30821@arm.com> (raw)
In-Reply-To: <bd403b9f-bb38-a456-b176-b6fefccb711f@arm.com>
On Thu, Mar 11, 2021 at 03:00:26PM +0000, Vincenzo Frascino wrote:
> On 3/11/21 1:25 PM, Catalin Marinas wrote:
> > On Mon, Mar 08, 2021 at 04:14:34PM +0000, Vincenzo Frascino wrote:
> >> load_unaligned_zeropad() and __get/put_kernel_nofault() functions can
> >> read passed some buffer limits which may include some MTE granule with a
> >> different tag.
> >>
> >> When MTE async mode is enable, the load operation crosses the boundaries
> >> and the next granule has a different tag the PE sets the TFSR_EL1.TF1
> >> bit as if an asynchronous tag fault is happened:
> >>
> >> ==================================================================
> >> BUG: KASAN: invalid-access
> >> Asynchronous mode enabled: no access details available
> >>
> >> CPU: 0 PID: 1 Comm: init Not tainted 5.12.0-rc1-ge1045c86620d-dirty #8
> >> Hardware name: FVP Base RevC (DT)
> >> Call trace:
> >> dump_backtrace+0x0/0x1c0
> >> show_stack+0x18/0x24
> >> dump_stack+0xcc/0x14c
> >> kasan_report_async+0x54/0x70
> >> mte_check_tfsr_el1+0x48/0x4c
> >> exit_to_user_mode+0x18/0x38
> >> finish_ret_to_user+0x4/0x15c
> >> ==================================================================
> >>
> >> Verify that Tag Check Override (TCO) is enabled in these functions before
> >> the load and disable it afterwards to prevent this to happen.
> >>
> >> Note: The issue has been observed only with an MTE enabled userspace.
> >
> > The above bug is all about kernel buffers. While userspace can trigger
> > the relevant code paths, it should not matter whether the user has MTE
> > enabled or not. Can you please confirm that you can still triggered the
> > fault with kernel-mode MTE but non-MTE user-space? If not, we may have a
> > bug somewhere as the two are unrelated: load_unaligned_zeropad() only
> > acts on kernel buffers and are subject to the kernel MTE tag check fault
> > mode.
>
> I retried and you are right, it does not matter if it is a MTE or non-MTE
> user-space. The issue seems to be that this test does not trigger the problem
> all the times which probably lead me to the wrong conclusions.
Keep the test around for some quick checks before you get the kasan
test support.
> > I don't think we should have a user-space selftest for this. The bug is
> > not about a user-kernel interface, so an in-kernel test is more
> > appropriate. Could we instead add this to the kasan tests and calling
> > load_unaligned_zeropad() and other functions directly?
>
> I agree with you we should abandon this strategy of triggering the issue due to
> my comment above. I will investigate the option of having a kasan test and try
> to come up with one that calls the relevant functions directly. I would prefer
> though, since the rest of the series is almost ready, to post it in a future
> series. What do you think?
That's fine by me.
--
Catalin
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next prev parent reply other threads:[~2021-03-11 16:30 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-08 16:14 [PATCH v14 0/8] arm64: ARMv8.5-A: MTE: Add async mode support Vincenzo Frascino
2021-03-08 16:14 ` [PATCH v14 1/8] arm64: mte: Add asynchronous " Vincenzo Frascino
2021-03-08 16:14 ` [PATCH v14 2/8] kasan: Add KASAN mode kernel parameter Vincenzo Frascino
2021-03-08 16:14 ` [PATCH v14 3/8] arm64: mte: Drop arch_enable_tagging() Vincenzo Frascino
2021-03-11 10:38 ` Catalin Marinas
2021-03-08 16:14 ` [PATCH v14 4/8] kasan: Add report for async mode Vincenzo Frascino
2021-03-08 16:14 ` [PATCH v14 5/8] arm64: mte: Enable TCO in functions that can read beyond buffer limits Vincenzo Frascino
2021-03-08 18:09 ` Mark Rutland
2021-03-09 10:26 ` Vincenzo Frascino
2021-03-08 21:58 ` kernel test robot
2021-03-09 0:28 ` kernel test robot
2021-03-09 22:40 ` kernel test robot
2021-03-08 16:14 ` [PATCH v14 6/8] arm64: mte: Enable async tag check fault Vincenzo Frascino
2021-03-08 16:14 ` [PATCH v14 7/8] arm64: mte: Report async tag faults before suspend Vincenzo Frascino
2021-03-08 16:14 ` [PATCH v14 8/8] kselftest/arm64: Verify that TCO is enabled in load_unaligned_zeropad() Vincenzo Frascino
2021-03-11 13:25 ` Catalin Marinas
2021-03-11 15:00 ` Vincenzo Frascino
2021-03-11 16:28 ` Catalin Marinas [this message]
2021-03-11 16:34 ` Vincenzo Frascino
2021-03-08 21:02 ` [PATCH v14 0/8] arm64: ARMv8.5-A: MTE: Add async mode support Andrey Konovalov
2021-03-09 10:11 ` Vincenzo Frascino
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