linux-kernel - Re: [PATCH v9 32/44] arm64: mte: Switch GCR

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Date:   Thu, 12 Nov 2020 09:45:53 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     Andrey Konovalov <andreyknvl@...gle.com>,
        Will Deacon <will.deacon@....com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Branislav Rankov <Branislav.Rankov@....com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kasan-dev@...glegroups.com, linux-arm-kernel@...ts.infradead.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 32/44] arm64: mte: Switch GCR_EL1 in kernel entry and
 exit

On Thu, Nov 12, 2020 at 09:45:45AM +0000, Vincenzo Frascino wrote:
> On 11/12/20 9:39 AM, Catalin Marinas wrote:
> > On Tue, Nov 10, 2020 at 11:10:29PM +0100, Andrey Konovalov wrote:
> >> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
> >> index 664c968dc43c..dbda6598c19d 100644
> >> --- a/arch/arm64/kernel/mte.c
> >> +++ b/arch/arm64/kernel/mte.c
> >> @@ -129,6 +131,26 @@ void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
> >>  	return ptr;
> >>  }
> >>  
> >> +void mte_init_tags(u64 max_tag)
> >> +{
> >> +	static bool gcr_kernel_excl_initialized = false;
> >> +
> >> +	if (!gcr_kernel_excl_initialized) {
> >> +		/*
> >> +		 * The format of the tags in KASAN is 0xFF and in MTE is 0xF.
> >> +		 * This conversion extracts an MTE tag from a KASAN tag.
> >> +		 */
> >> +		u64 incl = GENMASK(FIELD_GET(MTE_TAG_MASK >> MTE_TAG_SHIFT,
> >> +					     max_tag), 0);
> >> +
> >> +		gcr_kernel_excl = ~incl & SYS_GCR_EL1_EXCL_MASK;
> >> +		gcr_kernel_excl_initialized = true;
> >> +	}
> >> +
> >> +	/* Enable the kernel exclude mask for random tags generation. */
> >> +	write_sysreg_s(SYS_GCR_EL1_RRND | gcr_kernel_excl, SYS_GCR_EL1);
> >> +}
> > 
> > I don't think this function belongs to this patch. There is an earlier
> > patch that talks about mte_init_tags() but no trace of it until this
> > patch.
> 
> Could you please point out to which patch are you referring to?

I replied to it already (or you can search ;)). But this patch is about
switching GCR_EL1 on exception entry/exit rather than setting up the
initial kernel GCR_EL1 value.

-- 
Catalin