KVM: PPC: Book3S HV: Restore critical SPRs to host values on guest exit

commit 4c3bb4cc upstream.

This restores several special-purpose registers (SPRs) to sane values
on guest exit that were missed before.

TAR and VRSAVE are readable and writable by userspace, and we need to
save and restore them to prevent the guest from potentially affecting
userspace execution (not that TAR or VRSAVE are used by any known
program that run uses the KVM_RUN ioctl).  We save/restore these
in kvmppc_vcpu_run_hv() rather than on every guest entry/exit.

FSCR affects userspace execution in that it can prohibit access to
certain facilities by userspace.  We restore it to the normal value
for the task on exit from the KVM_RUN ioctl.

IAMR is normally 0, and is restored to 0 on guest exit.  However,
with a radix host on POWER9, it is set to a value that prevents the
kernel from executing user-accessible memory.  On POWER9, we save
IAMR on guest entry and restore it on guest exit to the saved value
rather than 0.  On POWER8 we continue to set it to 0 on guest exit.

PSPB is normally 0.  We restore it to 0 on guest exit to prevent
userspace taking advantage of the guest having set it non-zero
(which would allow userspace to set its SMT priority to high).

UAMOR is normally 0.  We restore it to 0 on guest exit to prevent
the AMR from being used as a covert channel between userspace
processes, since the AMR is not context-switched at present.

[paulus@ozlabs.org - removed IAMR bits that are only needed on POWER9;
 adjusted FSCR save/restore for lack of fscr field in thread_struct.]

Fixes: b005255e ("KVM: PPC: Book3S HV: Context-switch new POWER8 SPRs", 2014-01-08)
Cc: stable@vger.kernel.org # v3.14+
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/powerpc/kvm/book3s_hv.c

@@ -1951,6 +1951,9 @@ static int kvmppc_vcpu_run_hv(struct kvm_run *run, struct kvm_vcpu *vcpu)
 	int r;
 	int srcu_idx;
 	unsigned long ebb_regs[3] = {};	/* shut up GCC */
+	unsigned long user_tar = 0;
+	unsigned long proc_fscr = 0;
+	unsigned int user_vrsave;
 
 	if (!vcpu->arch.sane) {
 		run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
@@ -2001,12 +2004,15 @@ static int kvmppc_vcpu_run_hv(struct kvm_run *run, struct kvm_vcpu *vcpu)
 	flush_altivec_to_thread(current);
 	flush_vsx_to_thread(current);
 
-	/* Save userspace EBB register values */
+	/* Save userspace EBB and other register values */
 	if (cpu_has_feature(CPU_FTR_ARCH_207S)) {
 		ebb_regs[0] = mfspr(SPRN_EBBHR);
 		ebb_regs[1] = mfspr(SPRN_EBBRR);
 		ebb_regs[2] = mfspr(SPRN_BESCR);
+		user_tar = mfspr(SPRN_TAR);
+		proc_fscr = mfspr(SPRN_FSCR);
 	}
+	user_vrsave = mfspr(SPRN_VRSAVE);
 
 	vcpu->arch.wqp = &vcpu->arch.vcore->wq;
 	vcpu->arch.pgdir = current->mm->pgd;
@@ -2027,12 +2033,15 @@ static int kvmppc_vcpu_run_hv(struct kvm_run *run, struct kvm_vcpu *vcpu)
 		}
 	} while (is_kvmppc_resume_guest(r));
 
-	/* Restore userspace EBB register values */
+	/* Restore userspace EBB and other register values */
 	if (cpu_has_feature(CPU_FTR_ARCH_207S)) {
 		mtspr(SPRN_EBBHR, ebb_regs[0]);
 		mtspr(SPRN_EBBRR, ebb_regs[1]);
 		mtspr(SPRN_BESCR, ebb_regs[2]);
+		mtspr(SPRN_TAR, user_tar);
+		mtspr(SPRN_FSCR, proc_fscr);
 	}
+	mtspr(SPRN_VRSAVE, user_vrsave);
 
  out:
 	vcpu->arch.state = KVMPPC_VCPU_NOTREADY;

arch/powerpc/kvm/book3s_hv_rmhandlers.S

@@ -1182,6 +1182,7 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
 	mtspr	SPRN_IAMR, r0
 	mtspr	SPRN_CIABR, r0
 	mtspr	SPRN_DAWRX, r0
+	mtspr	SPRN_PSPB, r0
 	mtspr	SPRN_TCSCR, r0
 	mtspr	SPRN_WORT, r0
 	/* Set MMCRS to 1<<31 to freeze and disable the SPMC counters */
@@ -1198,6 +1199,7 @@ BEGIN_FTR_SECTION
 	std	r6,VCPU_UAMOR(r9)
 	li	r6,0
 	mtspr	SPRN_AMR,r6
+	mtspr	SPRN_UAMOR, r6
 END_FTR_SECTION_IFSET(CPU_FTR_ARCH_206)
 
 	/* Switch DSCR back to host value */