linux-kernel - Re: [PATCH 17/35] arm64/traps: Handle GCS exceptions

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Date:   Mon, 17 Jul 2023 13:12:30 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Mark Brown <broonie@...nel.org>
CC:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        "Suzuki K Poulose" <suzuki.poulose@....com>,
        Arnd Bergmann <arnd@...db.de>,
        "Oleg Nesterov" <oleg@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        "Kees Cook" <keescook@...omium.org>, Shuah Khan <shuah@...nel.org>,
        "Rick P. Edgecombe" <rick.p.edgecombe@...el.com>,
        Deepak Gupta <debug@...osinc.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>,
        "H.J. Lu" <hjl.tools@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-doc@...r.kernel.org>, <kvmarm@...ts.linux.dev>,
        <linux-fsdevel@...r.kernel.org>, <linux-arch@...r.kernel.org>,
        <linux-mm@...ck.org>, <linux-kselftest@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH 17/35] arm64/traps: Handle GCS exceptions

On Sun, 16 Jul 2023 22:51:13 +0100
Mark Brown <broonie@...nel.org> wrote:

> A new exception code is defined for GCS specific faults other than
> standard load/store faults, for example GCS token validation failures,
> add handling for this. These faults are reported to userspace as
> segfaults with code SEGV_CPERR (protection error), mirroring the
> reporting for x86 shadow stack errors.
> 
> GCS faults due to memory load/store operations generate data aborts with
> a flag set, these will be handled separately as part of the data abort
> handling.
> 
> Since we do not currently enable GCS for EL1 we should not get any faults
> there but while we're at it we wire things up there, treating any GCS
> fault as fatal.
> 
> Signed-off-by: Mark Brown <broonie@...nel.org>

See below.

> ---
>  arch/arm64/include/asm/esr.h       | 26 +++++++++++++++++++++++++-
>  arch/arm64/include/asm/exception.h |  2 ++
>  arch/arm64/kernel/entry-common.c   | 23 +++++++++++++++++++++++
>  arch/arm64/kernel/traps.c          | 11 +++++++++++
>  4 files changed, 61 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/esr.h b/arch/arm64/include/asm/esr.h
> index ae35939f395b..c5a72172fcf1 100644
> --- a/arch/arm64/include/asm/esr.h
> +++ b/arch/arm64/include/asm/esr.h
...

> @@ -382,6 +383,29 @@
>  #define ESR_ELx_MOPS_ISS_SRCREG(esr)	(((esr) & (UL(0x1f) << 5)) >> 5)
>  #define ESR_ELx_MOPS_ISS_SIZEREG(esr)	(((esr) & (UL(0x1f) << 0)) >> 0)
>  
> +/* ISS field definitions for GCS */
> +#define ESR_ELx_ExType_SHIFT	(20)
> +#define ESR_ELx_ExType_MASK	GENMASK(23, 20)
> +#define ESR_ELx_Raddr_SHIFT	(14)

(10) ?

> +#define ESR_ELx_Raddr_MASK	GENMASK(14, 10)
> +#define ESR_ELx_Rn_SHIFT	(5)
> +#define ESR_ELx_Rn_MASK		GENMASK(9, 5)

I think this can also be ESR_ELx_RVALUE_MASK for some ExType
Worth adding that as well?

> +#define ESR_ELx_IT_SHIFT	(0)
> +#define ESR_ELx_IT_MASK		GENMASK(4, 0)
> +
> +#define ESR_ELx_ExType_DATA_CHECK	0
> +#define ESR_ELx_ExType_EXLOCK		1
> +#define ESR_ELx_ExType_STR		2
> +
> +#define ESR_ELx_IT_RET			0
> +#define ESR_ELx_IT_GCSPOPM		1
> +#define ESR_ELx_IT_RET_KEYA		2
> +#define ESR_ELx_IT_RET_KEYB		3
> +#define ESR_ELx_IT_GCSSS1		4
> +#define ESR_ELx_IT_GCSSS2		5
> +#define ESR_ELx_IT_GCSPOPCX		6
> +#define ESR_ELx_IT_GCSPOPX		7