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Message-Id: <1585634956.dtpgv9vena.naveen@linux.ibm.com>
Date: Tue, 31 Mar 2020 11:43:18 +0530
From: "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To: Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Christophe Leroy <christophe.leroy@....fr>,
Michael Ellerman <mpe@...erman.id.au>,
Paul Mackerras <paulus@...ba.org>
Cc: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 10/12] powerpc/entry32: Blacklist exception entry points
for kprobe.
Christophe Leroy wrote:
>
>
> Le 30/03/2020 à 19:08, Naveen N. Rao a écrit :
>> 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@....fr>
>>> ---
>>> arch/powerpc/kernel/entry_32.S | 7 +++++++
>>> 1 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:
>>> mfspr r0,SPRN_DSRR1
>>> stw r0,_DSRR1(r11)
>>> /* fall through */
>>> +_ASM_NOKPROBE_SYMBOL(mcheck_transfer_to_handler)
>>>
>>> .globl debug_transfer_to_handler
>>> debug_transfer_to_handler:
>>> @@ -59,6 +60,7 @@ debug_transfer_to_handler:
>>> mfspr r0,SPRN_CSRR1
>>> stw r0,_CSRR1(r11)
>>> /* fall through */
>>> +_ASM_NOKPROBE_SYMBOL(debug_transfer_to_handler)
>>>
>>> .globl crit_transfer_to_handler
>>> crit_transfer_to_handler:
>>> @@ -94,6 +96,7 @@ crit_transfer_to_handler:
>>> rlwinm r0,r1,0,0,(31 - THREAD_SHIFT)
>>> stw r0,KSP_LIMIT(r8)
>>> /* fall through */
>>> +_ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler)
>>> #endif
>>>
>>> #ifdef CONFIG_40x
>>> @@ -115,6 +118,7 @@ crit_transfer_to_handler:
>>> rlwinm r0,r1,0,0,(31 - THREAD_SHIFT)
>>> stw r0,KSP_LIMIT(r8)
>>> /* fall through */
>>> +_ASM_NOKPROBE_SYMBOL(crit_transfer_to_handler)
>>> #endif
>>>
>>> /*
>>> @@ -127,6 +131,7 @@ crit_transfer_to_handler:
>>> .globl transfer_to_handler_full
>>> transfer_to_handler_full:
>>> SAVE_NVGPRS(r11)
>>> +_ASM_NOKPROBE_SYMBOL(transfer_to_handler_full)
>>> /* fall through */
>>>
>>> .globl transfer_to_handler
>>> @@ -286,6 +291,8 @@ reenable_mmu:
>>> lwz r2, GPR2(r11)
>>> b fast_exception_return
>>> #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.
Ok, I see what you mean. 'reenable_mmu' can probably be moved after the
end of 'transfer_to_handler_cont' (as also removing what looks to be an
unused label '1' for the branch to trace_hardirqs_off), but that's a
minor thing. From the blacklisting point, this is not an issue.
- Naveen
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