linux-kernel - Re: [PATCH 2/2] riscv: Add KASAN support

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Message-ID: <cf7a4259-afa5-53e6-f8f2-c243339cc3e9@virtuozzo.com>
Date:   Thu, 22 Aug 2019 20:08:00 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Nick Hu <nickhu@...estech.com>,
        Christoph Hellwig <hch@...radead.org>
Cc:     Alan Quey-Liang Kao(高魁良) 
        <alankao@...estech.com>,
        "paul.walmsley@...ive.com" <paul.walmsley@...ive.com>,
        "palmer@...ive.com" <palmer@...ive.com>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>,
        "green.hu@...il.com" <green.hu@...il.com>,
        "deanbo422@...il.com" <deanbo422@...il.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "glider@...gle.com" <glider@...gle.com>,
        "dvyukov@...gle.com" <dvyukov@...gle.com>,
        "Anup.Patel@....com" <Anup.Patel@....com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "alexios.zavras@...el.com" <alexios.zavras@...el.com>,
        "atish.patra@....com" <atish.patra@....com>,
        離職Zong Zong-Xian Li(李宗憲) 
        <zong@...estech.com>,
        "kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>
Subject: Re: [PATCH 2/2] riscv: Add KASAN support



On 8/14/19 10:44 AM, Nick Hu wrote:

>>
>>> diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
>>> index 23cd1a9..9700980 100644
>>> --- a/arch/riscv/kernel/vmlinux.lds.S
>>> +++ b/arch/riscv/kernel/vmlinux.lds.S
>>> @@ -46,6 +46,7 @@ SECTIONS
>>>  		KPROBES_TEXT
>>>  		ENTRY_TEXT
>>>  		IRQENTRY_TEXT
>>> +		SOFTIRQENTRY_TEXT
>>
>> Hmm.  What is the relation to kasan here?  Maybe we should add this
>> separately with a good changelog?
>>
> There is a commit for it:
> 
> Author: Alexander Potapenko <glider@...gle.com>
> Date:   Fri Mar 25 14:22:05 2016 -0700
> 
>     arch, ftrace: for KASAN put hard/soft IRQ entries into separate sections
> 
>     KASAN needs to know whether the allocation happens in an IRQ handler.
>     This lets us strip everything below the IRQ entry point to reduce the
>     number of unique stack traces needed to be stored.
> 
>     Move the definition of __irq_entry to <linux/interrupt.h> so that the
>     users don't need to pull in <linux/ftrace.h>.  Also introduce the
>     __softirq_entry macro which is similar to __irq_entry, but puts the
>     corresponding functions to the .softirqentry.text section.
> 
> After reading the patch I understand that soft/hard IRQ entries should be
> separated for KASAN to work, but why?
> 

KASAN doesn't need soft/hard IRQ entries separated. KASAN wants to know the entry
point of IRQ (hard or soft) to filter out random non-irq part of the stacktrace before feeding it to
stack_depot_save. See filter_irq_stacks().