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From: Marc Zyngier <maz@kernel.org>
To: Andrew Scull <ascull@google.com>
Cc: kernel-team@android.com, kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH] arm64: kvm: Stop clobbering x0 for HVC_SOFT_RESTART
Date: Mon, 06 Jul 2020 11:11:15 +0100	[thread overview]
Message-ID: <a765085746f61ed8deff396fae1d89a1@kernel.org> (raw)
In-Reply-To: <20200706095259.1338221-1-ascull@google.com>

On 2020-07-06 10:52, Andrew Scull wrote:
> HVC_SOFT_RESTART is given values for x0-2 that it should installed
> before exiting to the new address so should not set x0 to stub HVC
> success or failure code.
> 
> Signed-off-by: Andrew Scull <ascull@google.com>
> ---
>  arch/arm64/kvm/hyp-init.S | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
> index 6e6ed5581eed..e76c0e89d48e 100644
> --- a/arch/arm64/kvm/hyp-init.S
> +++ b/arch/arm64/kvm/hyp-init.S
> @@ -136,11 +136,15 @@ SYM_CODE_START(__kvm_handle_stub_hvc)
> 
>  1:	cmp	x0, #HVC_RESET_VECTORS
>  	b.ne	1f
> -reset:
> +
>  	/*
> -	 * Reset kvm back to the hyp stub. Do not clobber x0-x4 in
> -	 * case we coming via HVC_SOFT_RESTART.
> +	 * Set the HVC_RESET_VECTORS return code before entering the common
> +	 * path so that we do not clobber x0-x2 in case we are coming via
> +	 * HVC_SOFT_RESTART.
>  	 */
> +	mov	x0, xzr
> +reset:
> +	/* Reset kvm back to the hyp stub. */
>  	mrs	x5, sctlr_el2
>  	mov_q	x6, SCTLR_ELx_FLAGS
>  	bic	x5, x5, x6		// Clear SCTL_M and etc
> @@ -151,7 +155,6 @@ reset:
>  	/* Install stub vectors */
>  	adr_l	x5, __hyp_stub_vectors
>  	msr	vbar_el2, x5
> -	mov	x0, xzr
>  	eret
> 
>  1:	/* Bad stub call */

Huh, nice catch. I wonder what the fuss is about kexec, really,
given that it is *that* broken. This deserves:

Fixes: af42f20480bf1 ("arm64: hyp-stub: Zero x0 on successful stub 
handling")
Cc: stable@vger.kernel.org

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...
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  reply	other threads:[~2020-07-06 10:11 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-06  9:52 [PATCH] arm64: kvm: Stop clobbering x0 for HVC_SOFT_RESTART Andrew Scull
2020-07-06 10:11 ` Marc Zyngier [this message]
2020-07-08 16:22   ` James Morse
2020-07-06 10:29 ` Marc Zyngier

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