On Tue, Oct 24, 2023 at 01:08:53AM -0700, Pawan Gupta wrote: >During VMentry VERW is executed to mitigate MDS. After VERW, any memory >access like register push onto stack may put host data in MDS affected >CPU buffers. A guest can then use MDS to sample host data. > >Although likelihood of secrets surviving in registers at current VERW >callsite is less, but it can't be ruled out. Harden the MDS mitigation >by moving the VERW mitigation late in VMentry path. > >Note that VERW for MMIO Stale Data mitigation is unchanged because of >the complexity of per-guest conditional VERW which is not easy to handle >that late in asm with no GPRs available. If the CPU is also affected by >MDS, VERW is unconditionally executed late in asm regardless of guest >having MMIO access. > >Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx> >--- > arch/x86/kvm/vmx/vmenter.S | 4 ++++ > arch/x86/kvm/vmx/vmx.c | 10 +++++++--- > 2 files changed, 11 insertions(+), 3 deletions(-) > >diff --git a/arch/x86/kvm/vmx/vmenter.S b/arch/x86/kvm/vmx/vmenter.S >index b3b13ec04bac..c566035938cc 100644 >--- a/arch/x86/kvm/vmx/vmenter.S >+++ b/arch/x86/kvm/vmx/vmenter.S >@@ -1,6 +1,7 @@ > /* SPDX-License-Identifier: GPL-2.0 */ > #include <linux/linkage.h> > #include <asm/asm.h> >+#include <asm/segment.h> This header is already included a few lines below: #include <asm/nospec-branch.h> #include <asm/percpu.h> #include <asm/segment.h> <--- > #include <asm/bitsperlong.h> > #include <asm/kvm_vcpu_regs.h> > #include <asm/nospec-branch.h>
