diff --git a/debian/changelog b/debian/changelog
index 3344fe2c8..d18d337f4 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -6,6 +6,8 @@ linux (4.18.10-2) UNRELEASED; urgency=medium
   [ Salvatore Bonaccorso ]
   * [arm64] KVM: Tighten guest core register access from userspace
     (CVE-2018-18021)
+  * [arm64] KVM: Sanitize PSTATE.M when being set from userspace
+    (CVE-2018-18021)
 
  -- Ben Hutchings <ben@decadent.org.uk>  Fri, 05 Oct 2018 18:09:26 +0100
 
diff --git a/debian/patches/bugfix/arm64/arm64-kvm-sanitize-pstate.m-when-being-set-from-user.patch b/debian/patches/bugfix/arm64/arm64-kvm-sanitize-pstate.m-when-being-set-from-user.patch
new file mode 100644
index 000000000..b7c81d02c
--- /dev/null
+++ b/debian/patches/bugfix/arm64/arm64-kvm-sanitize-pstate.m-when-being-set-from-user.patch
@@ -0,0 +1,58 @@
+From: Marc Zyngier <marc.zyngier@arm.com>
+Date: Thu, 27 Sep 2018 16:53:22 +0100
+Subject: arm64: KVM: Sanitize PSTATE.M when being set from userspace
+Origin: https://git.kernel.org/linus/2a3f93459d689d990b3ecfbe782fec89b97d3279
+Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2018-18021
+
+Not all execution modes are valid for a guest, and some of them
+depend on what the HW actually supports. Let's verify that what
+userspace provides is compatible with both the VM settings and
+the HW capabilities.
+
+Cc: <stable@vger.kernel.org>
+Fixes: 0d854a60b1d7 ("arm64: KVM: enable initialization of a 32bit vcpu")
+Reviewed-by: Christoffer Dall <christoffer.dall@arm.com>
+Reviewed-by: Mark Rutland <mark.rutland@arm.com>
+Reviewed-by: Dave Martin <Dave.Martin@arm.com>
+Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
+Signed-off-by: Will Deacon <will.deacon@arm.com>
+[carnil: Backport for 4.18: Cherrypick directly commit from 4.18.12 /
+926415e1e4c9]
+---
+ arch/arm64/kvm/guest.c | 10 +++++++++-
+ 1 file changed, 9 insertions(+), 1 deletion(-)
+
+diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
+index 4a177629862b..d5c6bb1562d8 100644
+--- a/arch/arm64/kvm/guest.c
++++ b/arch/arm64/kvm/guest.c
+@@ -152,17 +152,25 @@ static int set_core_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
+ 	}
+ 
+ 	if (off == KVM_REG_ARM_CORE_REG(regs.pstate)) {
+-		u32 mode = (*(u32 *)valp) & COMPAT_PSR_MODE_MASK;
++		u64 mode = (*(u64 *)valp) & COMPAT_PSR_MODE_MASK;
+ 		switch (mode) {
+ 		case COMPAT_PSR_MODE_USR:
++			if (!system_supports_32bit_el0())
++				return -EINVAL;
++			break;
+ 		case COMPAT_PSR_MODE_FIQ:
+ 		case COMPAT_PSR_MODE_IRQ:
+ 		case COMPAT_PSR_MODE_SVC:
+ 		case COMPAT_PSR_MODE_ABT:
+ 		case COMPAT_PSR_MODE_UND:
++			if (!vcpu_el1_is_32bit(vcpu))
++				return -EINVAL;
++			break;
+ 		case PSR_MODE_EL0t:
+ 		case PSR_MODE_EL1t:
+ 		case PSR_MODE_EL1h:
++			if (vcpu_el1_is_32bit(vcpu))
++				return -EINVAL;
+ 			break;
+ 		default:
+ 			err = -EINVAL;
+-- 
+2.11.0
+
diff --git a/debian/patches/series b/debian/patches/series
index def369bd9..174480bdd 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -146,6 +146,7 @@ bugfix/all/floppy-Do-not-copy-a-kernel-pointer-to-user-memory-i.patch
 bugfix/all/scsi-target-iscsi-Use-hex2bin-instead-of-a-re-implem.patch
 bugfix/all/scsi-target-iscsi-Use-bin2hex-instead-of-a-re-implem.patch
 bugfix/arm64/arm64-kvm-tighten-guest-core-register-access-from-us.patch
+bugfix/arm64/arm64-kvm-sanitize-pstate.m-when-being-set-from-user.patch
 
 # Fix exported symbol versions
 bugfix/all/module-disable-matching-missing-version-crc.patch