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From:   Andrey Konovalov <andreyknvl@google.com>
Date:   Thu, 27 Aug 2020 14:34:31 +0200
Message-ID: <CAAeHK+zO8EJrmX5NjkKTB35eot1rDLjoqGyfoqF_quDV=VEvrQ@mail.gmail.com>
Subject: Re: [PATCH 32/35] kasan, arm64: print report from tag fault handler
To:     Catalin Marinas <catalin.marinas@arm.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc:     Dmitry Vyukov <dvyukov@google.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Marco Elver <elver@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        Elena Petrova <lenaptr@google.com>,
        Branislav Rankov <Branislav.Rankov@arm.com>,
        Kevin Brodsky <kevin.brodsky@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Thu, Aug 27, 2020 at 12:48 PM Catalin Marinas
<catalin.marinas@arm.com> 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 was considering that we can enable in-kernel MTE without enabling
CONFIG_KASAN_HW_TAGS, but perhaps this isn't what we want. I'll drop
this part in v2, but then we also need to make sure that in-kernel MTE
is only enabled when CONFIG_KASAN_HW_TAGS is enabled. Do we need more
ifdefs in arm64 patches when we write to MTE-related registers, or
does this work as is?