Patch "KVM: PPC: Book3S HV: Sanitize special-purpose register values on guest exit" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

KVM: PPC: Book3S HV: Sanitize special-purpose register values on guest exit

to the 3.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-ppc-book3s-hv-sanitize-special-purpose-register-values-on-guest-exit.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Paul Mackerras <[email protected]>
Date: Sat, 5 Mar 2016 19:34:39 +1100
Subject: KVM: PPC: Book3S HV: Sanitize special-purpose register values on guest exit

From: Paul Mackerras <[email protected]>

commit ccec44563b18a0ce90e2d4f332784b3cb25c8e9c upstream.

Thomas Huth discovered that a guest could cause a hard hang of a host CPU by setting the Instruction Authority Mask Register (IAMR) to a suitable value. It turns out that this is because when the code was added to context-switch the new special-purpose registers (SPRs) that were added in POWER8, we forgot to add code to ensure that they were restored to a sane value on guest exit.

This adds code to set those registers where a bad value could compromise the execution of the host kernel to a suitable neutral value on guest exit.

---
 arch/powerpc/kvm/book3s_hv_rmhandlers.S |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

@@ -1148,6 +1148,20 @@ END_FTR_SECTION_IFCLR(CPU_FTR_ARCH_207S)
 	std	r6, VCPU_ACOP(r9)
 	stw	r7, VCPU_GUEST_PID(r9)
 	std	r8, VCPU_WORT(r9)
+	/*
+	 * Restore various registers to 0, where non-zero values
+	 * set by the guest could disrupt the host.
+	 */
+	li	r0, 0
+	mtspr	SPRN_IAMR, r0
+	mtspr	SPRN_CIABR, r0
+	mtspr	SPRN_DAWRX, r0
+	mtspr	SPRN_TCSCR, r0
+	mtspr	SPRN_WORT, r0
+	/* Set MMCRS to 1<<31 to freeze and disable the SPMC counters */
+	li	r0, 1
+	sldi	r0, r0, 31
+	mtspr	SPRN_MMCRS, r0
 8:
 
 	/* Save and reset AMR and UAMOR before turning on the MMU */

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/kvm-ppc-book3s-hv-sanitize-special-purpose-register-values-on-guest-exit.patch