Re: [PATCH 10/12] powerpc/entry32: Blacklist exception entry points for kprobe.

[Christophe Leroy]

Le 30/03/2020 Ã 19:08, Naveen N. Rao a ÃcritÂ:
> Christophe Leroy wrote:
> > kprobe does not handle events happening in real mode.
> >
> > As exception entry points are running with MMU disabled,
> > blacklist them.
> >
> > Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
> > ---
> > Âarch/powerpc/kernel/entry_32.S | 7 +++++++
> > Â1 file changed, 7 insertions(+)
> >
> > diff --git a/arch/powerpc/kernel/entry_32.S 
> > b/arch/powerpc/kernel/entry_32.S
> > index 94f78c03cb79..9a1a45d6038a 100644
> > --- a/arch/powerpc/kernel/entry_32.S
> > +++ b/arch/powerpc/kernel/entry_32.S
> > @@ -51,6 +51,7 @@ mcheck_transfer_to_handler:
> > ÂÂÂÂ mfsprÂÂÂ r0,SPRN_DSRR1
> > ÂÂÂÂ stwÂÂÂ r0,_DSRR1(r11)
> > ÂÂÂÂ /* fall through */
> > +_ASM_NOKPROBE_SYMBOL(mcheck_transfer_to_handler)
> >
> > ÂÂÂÂ .globlÂÂÂ debug_transfer_to_handler
> > Âdebug_transfer_to_handler:
> > @@ -59,6 +60,7 @@ debug_transfer_to_handler:
> > ÂÂÂÂ mfsprÂÂÂ r0,SPRN_CSRR1
> > ÂÂÂÂ stwÂÂÂ r0,_CSRR1(r11)
> > ÂÂÂÂ /* fall through */
> > +_ASM_NOKPROBE_SYMBOL(debug_transfer_to_handler)
> >
> > ÂÂÂÂ .globlÂÂÂ crit_transfer_to_handler
> > Âcrit_transfer_to_handler:
> > @@ -94,6 +96,7 @@ crit_transfer_to_handler:
> > ÂÂÂÂ rlwinmÂÂÂ r0,r1,0,0,(31 - THREAD_SHIFT)
> > ÂÂÂÂ stwÂÂÂ r0,KSP_LIMIT(r8)
> > ÂÂÂÂ /* fall through */
> > +_ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler)
> > Â#endif
> >
> > Â#ifdef CONFIG_40x
> > @@ -115,6 +118,7 @@ crit_transfer_to_handler:
> > ÂÂÂÂ rlwinmÂÂÂ r0,r1,0,0,(31 - THREAD_SHIFT)
> > ÂÂÂÂ stwÂÂÂ r0,KSP_LIMIT(r8)
> > ÂÂÂÂ /* fall through */
> > +_ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler)
> > Â#endif
> >
> > Â/*
> > @@ -127,6 +131,7 @@ crit_transfer_to_handler:
> > ÂÂÂÂ .globlÂÂÂ transfer_to_handler_full
> > Âtransfer_to_handler_full:
> > ÂÂÂÂ SAVE_NVGPRS(r11)
> > +_ASM_NOKPROBE_SYMBOL(transfer_to_handler_full)
> > ÂÂÂÂ /* fall through */
> >
> > ÂÂÂÂ .globlÂÂÂ transfer_to_handler
> > @@ -286,6 +291,8 @@ reenable_mmu:
> > ÂÂÂÂ lwzÂÂÂ r2, GPR2(r11)
> > ÂÂÂÂ bÂÂÂ fast_exception_return
> > Â#endif
> > +_ASM_NOKPROBE_SYMBOL(transfer_to_handler)
> > +_ASM_NOKPROBE_SYMBOL(transfer_to_handler_cont)
>
> These are added after 'reenable_mmu', which is itself not blacklisted. 
> Is that intentional?

Yes I put it as the complete end of the entry part, ie just before 
stack_ovf which is a function by itself.

Note that reenable_mmu is inside an #ifdef CONFIG_TRACE_IRQFLAGS.

I'm not completely sure where to put the _ASM_NOKPROBE_SYMBOL()s, that's 
the reason why I put it close to the symbol itself in my first series.

Could you have a look at the code and tell me what looks the most 
appropriate as a location to you ?

https://elixir.bootlin.com/linux/v5.6/source/arch/powerpc/kernel/entry_32.S#L230

Thanks
Christophe