Messages in this thread | | | Subject | Re: [PATCH v14 8/8] kselftest/arm64: Verify that TCO is enabled in load_unaligned_zeropad() | From | Vincenzo Frascino <> | Date | Thu, 11 Mar 2021 16:34:15 +0000 |
| |
On 3/11/21 4:28 PM, Catalin Marinas wrote: > 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. >
Of course, I never throw away my code.
>>> 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. >
-- Regards, Vincenzo
| |