From bd89870c4447cbf622dd50d4d179e26234833600 Mon Sep 17 00:00:00 2001 From: Paul Mackerras Date: Wed, 22 Jun 2016 15:52:55 +1000 Subject: KVM: PPC: Book3S HV: Save/restore TM state in H_CEDE [ Upstream commit 93d17397e4e2182fdaad503e2f9da46202c0f1c3 ] 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 Signed-off-by: Sasha Levin --- arch/powerpc/kvm/book3s_hv_rmhandlers.S | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'arch/powerpc') diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S index fa3c669cbaf9..11d82b91aa4f 100644 --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S @@ -1931,6 +1931,13 @@ _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 @@ -2007,6 +2014,12 @@ 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 -- cgit v1.2.3