Re: [PATCH v2] arm64: disable kasan when accessing frame->fp in unwind_frame

[Will Deacon]

On Tue, Feb 09, 2016 at 09:17:12AM -0800, Shi, Yang wrote:
> On 2/9/2016 8:54 AM, Will Deacon wrote:
> >On Mon, Feb 08, 2016 at 09:13:09AM -0800, Yang Shi wrote:
> >>When boot arm64 kernel with KASAN enabled, the below error is reported by
> >>kasan:
> >>
> >>BUG: KASAN: out-of-bounds in unwind_frame+0xec/0x260 at addr ffffffc064d57ba0
> >>Read of size 8 by task pidof/499
> >>page:ffffffbdc39355c0 count:0 mapcount:0 mapping:          (null) index:0x0
> >>flags: 0x0()
> >>page dumped because: kasan: bad access detected
> >>CPU: 2 PID: 499 Comm: pidof Not tainted 4.5.0-rc1 #119
> >>Hardware name: Freescale Layerscape 2085a RDB Board (DT)
> >>Call trace:
> >>[<ffffffc00008d078>] dump_backtrace+0x0/0x290
> >>[<ffffffc00008d32c>] show_stack+0x24/0x30
> >>[<ffffffc0006a981c>] dump_stack+0x8c/0xd8
> >>[<ffffffc0002e4400>] kasan_report_error+0x558/0x588
> >>[<ffffffc0002e4958>] kasan_report+0x60/0x70
> >>[<ffffffc0002e3188>] __asan_load8+0x60/0x78
> >>[<ffffffc00008c92c>] unwind_frame+0xec/0x260
> >>[<ffffffc000087e60>] get_wchan+0x110/0x160
> >>[<ffffffc0003b647c>] do_task_stat+0xb44/0xb68
> >>[<ffffffc0003b7730>] proc_tgid_stat+0x40/0x50
> >>[<ffffffc0003ac840>] proc_single_show+0x88/0xd8
> >>[<ffffffc000345be8>] seq_read+0x370/0x770
> >>[<ffffffc00030aba0>] __vfs_read+0xc8/0x1d8
> >>[<ffffffc00030c0ec>] vfs_read+0x94/0x168
> >>[<ffffffc00030d458>] SyS_read+0xb8/0x128
> >>[<ffffffc000086530>] el0_svc_naked+0x24/0x28
> >>Memory state around the buggy address:
> >>  ffffffc064d57a80: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 00 f4 f4
> >>  ffffffc064d57b00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >>>ffffffc064d57b80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >>                                   ^
> >>  ffffffc064d57c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >>  ffffffc064d57c80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> >>
> >>Since the shadow byte pointed by the report is 0, so it may mean it is just hit
> >>oob in non-current task. So, disable the instrumentation to silence these
> >>warnings.
> >
> >Curious, but how did you trigger this? I'm just trying to confirm that
> >mainline is affected, but my machine boots happily with KASAN and STACKTRACE
> >selected and I can cat /proc/self/{stack,stat} quite happily.
> >
> >What am I missing?
> 
> I'm using mainline 4.5-rc1 kernel with gcc 5.2. And, my rootfs is NFS
> mounted.
> 
> Not sure if other kernel configs, i.e tracing stuff will have impact on the
> trigger since I'm not using the defconfig.

If you could put your .config somewhere, that would be helpful, please.

Will