Re: [PATCH 2/2] riscv: Add KASAN support

From: Andrey Ryabinin <aryabinin@virtuozzo.com>
To: Nick Hu <nickhu@andestech.com>, Christoph Hellwig <hch@infradead.org>
Cc: "Alan Quey-Liang Kao(高魁良)" <alankao@andestech.com>,
	"paul.walmsley@sifive.com" <paul.walmsley@sifive.com>,
	"palmer@sifive.com" <palmer@sifive.com>,
	"aou@eecs.berkeley.edu" <aou@eecs.berkeley.edu>,
	"green.hu@gmail.com" <green.hu@gmail.com>,
	"deanbo422@gmail.com" <deanbo422@gmail.com>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"linux-riscv@lists.infradead.org"
	<linux-riscv@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"glider@google.com" <glider@google.com>,
	"dvyukov@google.com" <dvyukov@google.com>,
	"Anup.Patel@wdc.com" <Anup.Patel@wdc.com>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	"alexios.zavras@intel.com" <alexios.zavras@intel.com>,
	"atish.patra@wdc.com" <atish.patra@wdc.com>,
	"離職Zong Zong-Xian Li(李宗憲)" <zong@andestech.com>,
	"kasan-dev@googlegroups.com" <kasan-dev@googlegroups.com>
Subject: Re: [PATCH 2/2] riscv: Add KASAN support
Date: Thu, 22 Aug 2019 20:08:00 +0300	[thread overview]
Message-ID: <cf7a4259-afa5-53e6-f8f2-c243339cc3e9@virtuozzo.com> (raw)
In-Reply-To: <20190814074417.GA21929@andestech.com>

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@google.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().