From: Julien Grall <julien.grall@arm.com>
To: Kyle Temkin <ktemkin@binghamton.edu>, xen-devel@lists.xenproject.org
Cc: Wei Liu <wei.liu2@citrix.com>,
sstabellini@kernel.org, "Kyle J. Temkin" <temkink@ainfosec.com>
Subject: Re: [PATCH] xen/arm64: ensure that the correct SP is used for exceptions
Date: Tue, 3 May 2016 11:43:34 +0100 [thread overview]
Message-ID: <572880D6.3050201@arm.com> (raw)
In-Reply-To: <1461863647-9330-1-git-send-email-ktemkin@binghamton.edu>
(CC Wei for release-ack)
Hello Kyle,
On 28/04/16 18:14, Kyle Temkin wrote:
> From: "Kyle J. Temkin" <temkink@ainfosec.com>
>
> The ARMv8 architecture has a SPSel ("stack pointer selection") machine
> register that allows us to determine which exception level's stack
> pointer is loaded when an exception occurs. As we don't want to
> use the non-priveleged SP_EL0 stack pointer -- or even assume that SP_EL0
NIT: s/priveleged/privileged/
> points to a valid address in the hypervisor context-- we'll need to ensure
> that our EL2 code sets the SPSel to SP_ELn mode, so exceptions that trap
> to EL2 use the EL2 stack pointer.
>
> This corrects an issue that can manifest as a hang-on-IRQ on some
> arm64 cores if the firmware/bootloader has previously initialized SPSel
> to 0; in which case Xen's exceptions will incorrectly use an invalid SP_EL0,
> and will endlessly spin on the synchronous abort handler.
>
> Signed-off-by: Kyle Temkin <temkink@ainfosec.com>
Reviewed-by: Julien Grall <julien.grall@arm.com>
Wei, this is a bug-fix and I think it should go to Xen 4.7.
We would also need to backport this patch on Xen 4.4 -> Xen 4.6.
Regards,
> ---
> xen/arch/arm/arm64/head.S | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
> index 946e2c9..d5831f2 100644
> --- a/xen/arch/arm/arm64/head.S
> +++ b/xen/arch/arm/arm64/head.S
> @@ -361,6 +361,11 @@ skip_bss:
> ldr x0, =(HSCTLR_BASE)
> msr SCTLR_EL2, x0
>
> + /* Ensure that any exceptions encountered at EL2
> + * are handled using the EL2 stack pointer, rather
> + * than SP_EL0. */
> + msr spsel, #1
> +
> /* Rebuild the boot pagetable's first-level entries. The structure
> * is described in mm.c.
> *
>
--
Julien Grall
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next prev parent reply other threads:[~2016-05-03 10:43 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-28 17:14 [PATCH] xen/arm64: ensure that the correct SP is used for exceptions Kyle Temkin
2016-05-03 10:43 ` Julien Grall [this message]
2016-05-03 13:37 ` Wei Liu
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