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 15:00:26 +0000 |
| |
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.
> 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?
-- Regards, Vincenzo
| |