linux-kernel - Re: [PATCH v2] powerpc: Fix irq_soft_mask_set() and irq_soft_mask

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Date:   Tue, 30 Aug 2022 09:10:02 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Nicholas Piggin <npiggin@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Segher Boessenkool <segher@...nel.crashing.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Zhouyi Zhou <zhouzhouyi@...il.com>
Subject: Re: [PATCH v2] powerpc: Fix irq_soft_mask_set() and
 irq_soft_mask_return() with sanitizer



Le 30/08/2022 à 11:01, Nicholas Piggin a écrit :
> On Tue Aug 30, 2022 at 3:24 PM AEST, Christophe Leroy wrote:
>>> This is still slightly concerning to me. Is there any guarantee that the
>>> compiler would not use a different sequence for the address here?
>>>
>>> Maybe explicit r13 is required.
>>>
>>
>> local_paca is defined as:
>>
>> 	register struct paca_struct *local_paca asm("r13");
>>
>> Why would the compiler use another register ?
> 
> Hopefully it doesn't. Is it guaranteed that it won't?
> 
>> If so, do we also have an
>> issue with the use of current_stack_pointer in irq.c ?
> 
> What problems do you think it might have?  I think it may be okay
> because we're only using it to check what stack we are using so doesn't
> really matter what value it is when we sample it.
> 
> The overflow check similarly probably doesn't matter the exact value.
> 
>> Segher ?
> 
> I'm sure Segher will be delighted with the creative asm in __do_IRQ
> and call_do_irq :) *Grabs popcorn*
> 

Segher was in the loop, 
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/5ca6639b7c1c21ee4b4138b7cfb31d6245c4195c.1570684298.git.christophe.leroy@c-s.fr/