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

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Date:   Thu, 27 Aug 2020 13:11:37 +0100
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Elena Petrova <lenaptr@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Will Deacon <will.deacon@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 32/35] kasan, arm64: print report from tag fault handler



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