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

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Date:   Thu, 27 Aug 2020 11:48:16 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....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 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.

-- 
Catalin