Re: [RFC PATCH v1] powerpc: Enable KFENCE for PPC32

Marco Elver
2021-03-04T11:33:18Z

On Thu, 4 Mar 2021 at 12:23, Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
> Le 03/03/2021 à 11:56, Marco Elver a écrit :
> >
> > Somewhat tangentially, I also note that e.g. show_regs(regs) (which
> > was printed along the KFENCE report above) didn't include the top
> > frame in the "Call Trace", so this assumption is definitely not
> > isolated to KFENCE.
> >
>
> Now, I have tested PPC64 (with the patch I sent yesterday to modify save_stack_trace_regs()
> applied), and I get many failures. Any idea ?
>
> [ 17.653751][ T58] ==================================================================
> [ 17.654379][ T58] BUG: KFENCE: invalid free in .kfence_guarded_free+0x2e4/0x530
> [ 17.654379][ T58]
> [ 17.654831][ T58] Invalid free of 0xc00000003c9c0000 (in kfence-#77):
> [ 17.655358][ T58] .kfence_guarded_free+0x2e4/0x530
> [ 17.655775][ T58] .__slab_free+0x320/0x5a0
> [ 17.656039][ T58] .test_double_free+0xe0/0x198
> [ 17.656308][ T58] .kunit_try_run_case+0x80/0x110
> [ 17.656523][ T58] .kunit_generic_run_threadfn_adapter+0x38/0x50
> [ 17.657161][ T58] .kthread+0x18c/0x1a0
> [ 17.659148][ T58] .ret_from_kernel_thread+0x58/0x70
> [ 17.659869][ T58]
> [ 17.663954][ T58] kfence-#77 [0xc00000003c9c0000-0xc00000003c9c001f, size=32, cache=kmalloc-32]
> allocated by task 58:
> [ 17.666113][ T58] .__kfence_alloc+0x1bc/0x510
> [ 17.667069][ T58] .__kmalloc+0x280/0x4f0
> [ 17.667452][ T58] .test_alloc+0x19c/0x430
> [ 17.667732][ T58] .test_double_free+0x88/0x198
> [ 17.667971][ T58] .kunit_try_run_case+0x80/0x110
> [ 17.668283][ T58] .kunit_generic_run_threadfn_adapter+0x38/0x50
> [ 17.668553][ T58] .kthread+0x18c/0x1a0
> [ 17.669315][ T58] .ret_from_kernel_thread+0x58/0x70
> [ 17.669711][ T58]
> [ 17.669711][ T58] freed by task 58:
> [ 17.670116][ T58] .kfence_guarded_free+0x3d0/0x530
> [ 17.670421][ T58] .__slab_free+0x320/0x5a0
> [ 17.670603][ T58] .test_double_free+0xb4/0x198
> [ 17.670827][ T58] .kunit_try_run_case+0x80/0x110
> [ 17.671073][ T58] .kunit_generic_run_threadfn_adapter+0x38/0x50
> [ 17.671410][ T58] .kthread+0x18c/0x1a0
> [ 17.671618][ T58] .ret_from_kernel_thread+0x58/0x70
> [ 17.671972][ T58]
> [ 17.672638][ T58] CPU: 0 PID: 58 Comm: kunit_try_catch Tainted: G B
> 5.12.0-rc1-01540-g0783285cc1b8-dirty #4685
> [ 17.673768][ T58] ==================================================================
> [ 17.677031][ T58] # test_double_free: EXPECTATION FAILED at mm/kfence/kfence_test.c:380
> [ 17.677031][ T58] Expected report_matches(&expect) to be true, but is false
> [ 17.684397][ T1] not ok 7 - test_double_free
> [ 17.686463][ T59] # test_double_free-memcache: setup_test_cache: size=32, ctor=0x0
> [ 17.688403][ T59] # test_double_free-memcache: test_alloc: size=32, gfp=cc0, policy=any,
> cache=1

Looks like something is prepending '.' to function names. We expect
the function name to appear as-is, e.g. "kfence_guarded_free",
"test_double_free", etc.

Is there something special on ppc64, where the '.' is some convention?

Thanks,
-- Marco