Re: [PATCH 32/35] kasan, arm64: print report from tag fault handler

From: Vincenzo Frascino <vincenzo.frascino@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>,
	Andrey Konovalov <andreyknvl@google.com>
Cc: linux-arm-kernel@lists.infradead.org,
	Marco Elver <elver@google.com>,
	Elena Petrova <lenaptr@google.com>,
	Kevin Brodsky <kevin.brodsky@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Branislav Rankov <Branislav.Rankov@arm.com>,
	kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, Alexander Potapenko <glider@google.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Evgenii Stepanov <eugenis@google.com>
Subject: Re: [PATCH 32/35] kasan, arm64: print report from tag fault handler
Date: Thu, 27 Aug 2020 13:11:37 +0100	[thread overview]
Message-ID: <37de7524-b042-831f-6e43-30adf85c83a8@arm.com> (raw)
In-Reply-To: <20200827104816.GI29264@gaia>

On 8/27/20 11:48 AM, Catalin Marinas wrote:
> On Fri, Aug 14, 2020 at 07:27:14PM +0200, Andrey Konovalov wrote:
>> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
>> index c62c8ba85c0e..cf00b3942564 100644
>> --- a/arch/arm64/mm/fault.c
>> +++ b/arch/arm64/mm/fault.c
>> @@ -14,6 +14,7 @@
>>  #include <linux/mm.h>
>>  #include <linux/hardirq.h>
>>  #include <linux/init.h>
>> +#include <linux/kasan.h>
>>  #include <linux/kprobes.h>
>>  #include <linux/uaccess.h>
>>  #include <linux/page-flags.h>
>> @@ -314,11 +315,19 @@ static void report_tag_fault(unsigned long addr, unsigned int esr,
>>  {
>>  	bool is_write = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;
>>  
>> +#ifdef CONFIG_KASAN_HW_TAGS
>> +	/*
>> +	 * SAS bits aren't set for all faults reported in EL1, so we can't
>> +	 * find out access size.
>> +	 */
>> +	kasan_report(addr, 0, is_write, regs->pc);
>> +#else
>>  	pr_alert("Memory Tagging Extension Fault in %pS\n", (void *)regs->pc);
>>  	pr_alert("  %s at address %lx\n", is_write ? "Write" : "Read", addr);
>>  	pr_alert("  Pointer tag: [%02x], memory tag: [%02x]\n",
>>  			mte_get_ptr_tag(addr),
>>  			mte_get_mem_tag((void *)addr));
>> +#endif
>>  }
> 
> More dead code. So what's the point of keeping the pr_alert() introduced
> earlier? CONFIG_KASAN_HW_TAGS is always on for in-kernel MTE. If MTE is
> disabled, this function isn't called anyway.
> 

I agree we should remove them (togheter with '#ifdef CONFIG_KASAN_HW_TAGS') or
integrate them with the kasan code if still meaningful.

-- 
Regards,
Vincenzo

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