[PATCH 3.16.y-ckt 121/142] KVM: PPC: Book3S HV: Sanitize special-purpose register values on guest exit

From: Luis Henriques
Date: Tue Mar 22 2016 - 06:52:21 EST

3.16.7-ckt26 -stable review patch. If anyone has any objections, please let me know.


From: Paul Mackerras <paulus@xxxxxxxxx>

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.

Fixes: b005255e12a3
Reported-by: Thomas Huth <thuth@xxxxxxxxxx>
Reviewed-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Paul Mackerras <paulus@xxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
arch/powerpc/kvm/book3s_hv_rmhandlers.S | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index 6fafff75f24a..f3197994b733 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -1280,6 +1280,20 @@ 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

/* Save and reset AMR and UAMOR before turning on the MMU */