linux-kernel - Re: [PATCH v8 32/43] arm64: mte: Switch GCR

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Date:   Thu, 5 Nov 2020 17:30:34 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     Will Deacon <will.deacon@....com>,
        Vincenzo Frascino <vincenzo.frascino@....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 v8 32/43] arm64: mte: Switch GCR_EL1 in kernel entry and
 exit

On Thu, Nov 05, 2020 at 12:18:47AM +0100, Andrey Konovalov wrote:
> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
> index 14b0c19a33e3..cc7e0f8707f7 100644
> --- a/arch/arm64/kernel/mte.c
> +++ b/arch/arm64/kernel/mte.c
> @@ -23,6 +23,8 @@
>  #include <asm/ptrace.h>
>  #include <asm/sysreg.h>
>  
> +u64 gcr_kernel_excl __ro_after_init;
> +
>  static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap)
>  {
>  	pte_t old_pte = READ_ONCE(*ptep);
> @@ -123,6 +125,23 @@ void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
>  
>  void __init 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);

Same question as on a previous patch. Is SYS_GCR_EL1 written on the
other registers via cpu_enable_mte()?

-- 
Catalin