Re: [PATCH v2] powerpc/kprobes: Fix Oops by passing ppc_inst as a pointer to emulate_step() on ppc32

[Christophe Leroy]

Le 24/06/2021 à 12:59, Naveen N. Rao a écrit :
> Christophe Leroy wrote:
> > From: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
> >
> > Trying to use a kprobe on ppc32 results in the below splat:
> >     BUG: Unable to handle kernel data access on read at 0x7c0802a6
> >     Faulting instruction address: 0xc002e9f0
> >     Oops: Kernel access of bad area, sig: 11 [#1]
> >     BE PAGE_SIZE=4K PowerPC 44x Platform
> >     Modules linked in:
> >     CPU: 0 PID: 89 Comm: sh Not tainted 5.13.0-rc1-01824-g3a81c0495fdb #7
> >     NIP:  c002e9f0 LR: c0011858 CTR: 00008a47
> >     REGS: c292fd50 TRAP: 0300   Not tainted  (5.13.0-rc1-01824-g3a81c0495fdb)
> >     MSR:  00009000 <EE,ME>  CR: 24002002  XER: 20000000
> >     DEAR: 7c0802a6 ESR: 00000000
> >     <snip>
> >     NIP [c002e9f0] emulate_step+0x28/0x324
> >     LR [c0011858] optinsn_slot+0x128/0x10000
> >     Call Trace:
> >      opt_pre_handler+0x7c/0xb4 (unreliable)
> >      optinsn_slot+0x128/0x10000
> >      ret_from_syscall+0x0/0x28
> >
> > The offending instruction is:
> >     81 24 00 00     lwz     r9,0(r4)
> >
> > Here, we are trying to load the second argument to emulate_step():
> > struct ppc_inst, which is the instruction to be emulated. On ppc64,
> > structures are passed in registers when passed by value. However, per
> > the ppc32 ABI, structures are always passed to functions as pointers.
> > This isn't being adhered to when setting up the call to emulate_step()
> > in the optprobe trampoline. Fix the same.
> >
> > Fixes: eacf4c0202654a ("powerpc: Enable OPTPROBES on PPC32")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
> > ---
> > v2: Rebased on powerpc/merge 7f030e9d57b8
> > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
>
> Thanks for rebasing this!
>
> I think git am drops everything after three dashes, so applying this patch will drop your SOB. The 
> recommended style (*) for adding a changelog is to include it within [] before the second SOB.

Yes, I saw that after sending the mail. Usually I add a signed-off-by with 'git --amend -s' when I 
add the history, so it goes before the '---' I'm adding.

This time I must have forgotten the '-s' so it was added by the 'git format-patch -s' which is in my 
submit script, and so it was added at the end.

It's not really a big deal, up to Michael to either move it at the right place or discard it, I 
don't really mind. Do the easiest for you.

Thanks
Christophe