linux-kernel - Re: [PATCH 2/4] KVM: s390: vsie: Fix length of facility list shadowed

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Date:   Fri, 3 Nov 2023 19:34:21 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Nina Schoetterl-Glausch <nsg@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        David Hildenbrand <dahi@...ux.vnet.ibm.com>
Cc:     Cornelia Huck <cornelia.huck@...ibm.com>,
        linux-s390@...r.kernel.org, Sven Schnelle <svens@...ux.ibm.com>,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Michael Mueller <mimu@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/4] KVM: s390: vsie: Fix length of facility list shadowed

On 03.11.23 18:30, Nina Schoetterl-Glausch wrote:
> The length of the facility list accessed when interpretively executing
> STFLE is the same as the hosts facility list (in case of format-0)
> When shadowing, copy only those bytes.
> The memory following the facility list need not be accessible, in which
> case we'd wrongly inject a validity intercept.
> 
> Fixes: 66b630d5b7f2 ("KVM: s390: vsie: support STFLE interpretation")
> Signed-off-by: Nina Schoetterl-Glausch <nsg@...ux.ibm.com>
> ---
>   arch/s390/include/asm/facility.h |  6 ++++++
>   arch/s390/kernel/Makefile        |  2 +-
>   arch/s390/kernel/facility.c      | 18 ++++++++++++++++++
>   arch/s390/kvm/vsie.c             | 12 +++++++++++-
>   4 files changed, 36 insertions(+), 2 deletions(-)
>   create mode 100644 arch/s390/kernel/facility.c
> 
> diff --git a/arch/s390/include/asm/facility.h b/arch/s390/include/asm/facility.h
> index 94b6919026df..796007125dff 100644
> --- a/arch/s390/include/asm/facility.h
> +++ b/arch/s390/include/asm/facility.h
> @@ -111,4 +111,10 @@ static inline void stfle(u64 *stfle_fac_list, int size)
>   	preempt_enable();
>   }
>   
> +/**
> + * stfle_size - Actual size of the facility list as specified by stfle
> + * (number of double words)
> + */
> +unsigned int stfle_size(void);
> +
>   #endif /* __ASM_FACILITY_H */
> diff --git a/arch/s390/kernel/Makefile b/arch/s390/kernel/Makefile
> index 0df2b88cc0da..0daa81439478 100644
> --- a/arch/s390/kernel/Makefile
> +++ b/arch/s390/kernel/Makefile
> @@ -41,7 +41,7 @@ obj-y	+= sysinfo.o lgr.o os_info.o
>   obj-y	+= runtime_instr.o cache.o fpu.o dumpstack.o guarded_storage.o sthyi.o
>   obj-y	+= entry.o reipl.o kdebugfs.o alternative.o
>   obj-y	+= nospec-branch.o ipl_vmparm.o machine_kexec_reloc.o unwind_bc.o
> -obj-y	+= smp.o text_amode31.o stacktrace.o abs_lowcore.o
> +obj-y	+= smp.o text_amode31.o stacktrace.o abs_lowcore.o facility.o
>   
>   extra-y				+= vmlinux.lds
>   
> diff --git a/arch/s390/kernel/facility.c b/arch/s390/kernel/facility.c
> new file mode 100644
> index 000000000000..c33a95a562da
> --- /dev/null
> +++ b/arch/s390/kernel/facility.c
> @@ -0,0 +1,18 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright IBM Corp. 2023
> + */
> +
> +#include <asm/facility.h>
> +
> +unsigned int stfle_size(void)
> +{
> +	static unsigned int size = 0;
> +	u64 dummy;
> +
> +	if (!size) {
> +		size = __stfle_asm(&dummy, 1) + 1;
> +	}
> +	return size;
> +}
> +EXPORT_SYMBOL(stfle_size);

Possible races? Should have to use an atomic?

No access to documentation, but sounds plausible.

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb