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

[Marco Elver]

On Thu, Mar 04, 2021 at 12:48PM +0100, Christophe Leroy wrote:
> Le 04/03/2021 à 12:31, Marco Elver a écrit :
> > On Thu, 4 Mar 2021 at 12:23, Christophe Leroy
> > <christophe.leroy@xxxxxxxxxx> 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]
[...]
> > 
> > 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?
> > 
> 
> I think so, see https://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi.html#FUNC-DES
> 
> Also see commit https://github.com/linuxppc/linux/commit/02424d896

Thanks -- could you try the below patch? You'll need to define
ARCH_FUNC_PREFIX accordingly.

We think, since there are only very few architectures that add a prefix,
requiring <asm/kfence.h> to define something like ARCH_FUNC_PREFIX is
the simplest option. Let me know if this works for you.

There an alternative option, which is to dynamically figure out the
prefix, but if this simpler option is fine with you, we'd prefer it.

Thanks,
-- Marco

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