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SubjectRe: [PATCH 2/4] KVM: s390: vsie: Fix length of facility list shadowed
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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@linux.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@redhat.com>

--
Cheers,

David / dhildenb

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