linux-kernel - Re: [PATCH v11 18/39] arm64/traps: Handle GCS exceptions

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Message-ID: <ZsdczGTaMgZnEaDy@arm.com>
Date: Thu, 22 Aug 2024 16:44:12 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Mark Brown <broonie@...nel.org>
Cc: 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>,
	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>, Kees Cook <kees@...nel.org>,
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	Wilco Dijkstra <wilco.dijkstra@....com>,
	linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
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	linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v11 18/39] arm64/traps: Handle GCS exceptions

On Thu, Aug 22, 2024 at 02:15:21AM +0100, Mark Brown wrote:
> +static void noinstr el0_gcs(struct pt_regs *regs, unsigned long esr)
> +{
> +	enter_from_user_mode(regs);
> +	local_daif_restore(DAIF_PROCCTX);
> +	do_el0_gcs(regs, esr);
> +	exit_to_user_mode(regs);
> +}
> +
>  static void noinstr el0_inv(struct pt_regs *regs, unsigned long esr)
>  {
>  	enter_from_user_mode(regs);
> @@ -766,6 +786,9 @@ asmlinkage void noinstr el0t_64_sync_handler(struct pt_regs *regs)
>  	case ESR_ELx_EC_MOPS:
>  		el0_mops(regs, esr);
>  		break;
> +	case ESR_ELx_EC_GCS:
> +		el0_gcs(regs, esr);
> +		break;
>  	case ESR_ELx_EC_BREAKPT_LOW:
>  	case ESR_ELx_EC_SOFTSTP_LOW:
>  	case ESR_ELx_EC_WATCHPT_LOW:
> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> index 9e22683aa921..d410dcc12ed8 100644
> --- a/arch/arm64/kernel/traps.c
> +++ b/arch/arm64/kernel/traps.c
> @@ -500,6 +500,16 @@ void do_el1_bti(struct pt_regs *regs, unsigned long esr)
>  	die("Oops - BTI", regs, esr);
>  }
>  
> +void do_el0_gcs(struct pt_regs *regs, unsigned long esr)
> +{
> +	force_signal_inject(SIGSEGV, SEGV_CPERR, regs->pc, 0);
> +}

Just double checking: a GCSPOPM (for example, it can be a RET) from a
non-GCS page would generate a classic permission fault with ISS2.GCS set
rather than a GCS exception. That's my reading from the Arm ARM
pseudocode, the text isn't clear to me.

-- 
Catalin