[PATCH v4 2/4] KVM: s390: vsie: Fix length of facility list shadowed

Nina Schoetterl-Glausch
2023-12-19T14:09:01Z

The length of the facility list accessed when interpretively executing
STFLE is the same as the hosts facility list (in case of format-0)
The memory following the facility list doesn't need to be accessible.
The current VSIE implementation accesses a fixed length that exceeds the
guest/host facility list length and can therefore wrongly inject a
validity intercept.
Instead, find out the host facility list length by running STFLE and
copy only as much as necessary when shadowing.

Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
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 | 21 +++++++++++++++++++++
arch/s390/kvm/vsie.c | 12 +++++++++++-
4 files changed, 39 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 353def93973b..7a562b4199c8 100644
--- a/arch/s390/kernel/Makefile
+++ b/arch/s390/kernel/Makefile
@@ -41,7 +41,7 @@ obj-y += sysinfo.o lgr.o os_info.o ctlreg.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..f02127219a27
--- /dev/null
+++ b/arch/s390/kernel/facility.c
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright IBM Corp. 2023
+ */
+
+#include <asm/facility.h>
+
+unsigned int stfle_size(void)
+{
+ static unsigned int size;
+ unsigned int r;
+ u64 dummy;
+
+ r = READ_ONCE(size);
+ if (!r) {
+ r = __stfle_asm(&dummy, 1) + 1;
+ WRITE_ONCE(size, r);
+ }
+ return r;
+}
+EXPORT_SYMBOL(stfle_size);
diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
index 35937911724e..fef42e2a80a2 100644
--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -19,6 +19,7 @@
#include <asm/nmi.h>
#include <asm/dis.h>
#include <asm/fpu/api.h>
+#include <asm/facility.h>
#include "kvm-s390.h"
#include "gaccess.h"

@@ -986,6 +987,10 @@ static int handle_stfle(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
__u32 fac = READ_ONCE(vsie_page->scb_o->fac);

+ /*
+ * Alternate-STFLE-Interpretive-Execution facilities are not supported
+ * -> format-0 flcb
+ */
if (fac && test_kvm_facility(vcpu->kvm, 7)) {
retry_vsie_icpt(vsie_page);
/*
@@ -993,8 +998,13 @@ static int handle_stfle(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
* so we need to mask here before reading.
*/
fac = fac & 0x7ffffff8U;
+ /*
+ * format-0 -> size of nested guest's facility list == guest's size
+ * guest's size == host's size, since STFLE is interpretatively executed
+ * using a format-0 for the guest, too.
+ */
if (read_guest_real(vcpu, fac, &vsie_page->fac,
- sizeof(vsie_page->fac)))
+ stfle_size() * sizeof(u64)))
return set_validity_icpt(scb_s, 0x1090U);
scb_s->fac = (__u32)(__u64) &vsie_page->fac;
}
--
2.40.1