[PULL 29/41] KVM: PPC: Graciously fail broken LE hypercalls

Alexander Graf
2014-05-30T12:42:44Z

There are LE Linux guests out there that don't handle hypercalls correctly.
Instead of interpreting the instruction stream from device tree as big endian
they assume it's a little endian instruction stream and fail.

When we see an illegal instruction from such a byte reversed instruction stream,
bail out graciously and just declare every hcall as error.

Signed-off-by: Alexander Graf <agraf@suse.de>
---
arch/powerpc/kvm/book3s_emulate.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)

diff --git a/arch/powerpc/kvm/book3s_emulate.c b/arch/powerpc/kvm/book3s_emulate.c
index c992447..3f29526 100644
--- a/arch/powerpc/kvm/book3s_emulate.c
+++ b/arch/powerpc/kvm/book3s_emulate.c
@@ -94,8 +94,25 @@ int kvmppc_core_emulate_op_pr(struct kvm_run *run, struct kvm_vcpu *vcpu,
int rs = get_rs(inst);
int ra = get_ra(inst);
int rb = get_rb(inst);
+ u32 inst_sc = 0x44000002;

switch (get_op(inst)) {
+ case 0:
+ emulated = EMULATE_FAIL;
+ if ((kvmppc_get_msr(vcpu) & MSR_LE) &&
+ (inst == swab32(inst_sc))) {
+ /*
+ * This is the byte reversed syscall instruction of our
+ * hypercall handler. Early versions of LE Linux didn't
+ * swap the instructions correctly and ended up in
+ * illegal instructions.
+ * Just always fail hypercalls on these broken systems.
+ */
+ kvmppc_set_gpr(vcpu, 3, EV_UNIMPLEMENTED);
+ kvmppc_set_pc(vcpu, kvmppc_get_pc(vcpu) + 4);
+ emulated = EMULATE_DONE;
+ }
+ break;
case 19:
switch (get_xop(inst)) {
case OP_19_XOP_RFID:
--
1.8.1.4