@@ -2093,6 +2093,13 @@ _GLOBAL(kvmppc_h_cede) /* r3 = vcpu pointer, r11 = msr, r13 = paca */
/* save FP state */
bl kvmppc_save_fp
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+BEGIN_FTR_SECTION
+ ld r9, HSTATE_KVM_VCPU(r13)
+ bl kvmppc_save_tm
+END_FTR_SECTION_IFSET(CPU_FTR_TM)
+#endif
+
/*
* Set DEC to the smaller of DEC and HDEC, so that we wake
* no later than the end of our timeslice (HDEC interrupts
@@ -2169,6 +2176,12 @@ kvm_end_cede:
bl kvmhv_accumulate_time
#endif
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+BEGIN_FTR_SECTION
+ bl kvmppc_restore_tm
+END_FTR_SECTION_IFSET(CPU_FTR_TM)
+#endif
+
/* load up FP state */
bl kvmppc_load_fp
It turns out that if the guest does a H_CEDE while the CPU is in a transactional state, and the H_CEDE does a nap, and the nap loses the architected state of the CPU (which is is allowed to do), then we lose the checkpointed state of the virtual CPU. In addition, the transactional-memory state recorded in the MSR gets reset back to non-transactional, and when we try to return to the guest, we take a TM bad thing type of program interrupt because we are trying to transition from non-transactional to transactional with a hrfid instruction, which is not permitted. The result of the program interrupt occurring at that point is that the host CPU will hang in an infinite loop with interrupts disabled. Thus this is a denial of service vulnerability in the host which can be triggered by any guest (and depending on the guest kernel, it can potentially triggered by unprivileged userspace in the guest). This vulnerability has been assigned the ID CVE-2016-5412. To fix this, we save the TM state before napping and restore it on exit from the nap, when handling a H_CEDE in real mode. The case where H_CEDE exits to host virtual mode is already OK (as are other hcalls which exit to host virtual mode) because the exit path saves the TM state. Cc: stable@vger.kernel.org # v3.15+ Signed-off-by: Paul Mackerras <paulus@ozlabs.org> --- arch/powerpc/kvm/book3s_hv_rmhandlers.S | 13 +++++++++++++ 1 file changed, 13 insertions(+)