This is the backport of recently upstreamed series that moves VERW execution to a later point in exit-to-user path. This is needed because in some cases it may be possible for data accessed after VERW executions may end into MDS affected CPU buffers. Moving VERW closer to ring transition reduces the attack surface.
Patch 1/6 includes a minor fix that is queued for upstream: https://lore.kernel.org/lkml/170899674562.398.6398007479766564897.tip-bot2@t...
Patch 2/6 needed a conflict to be resolved for the hunk swapgs_restore_regs_and_return_to_usermode.
This is only compile and boot tested on qemu.
Cc: Dave Hansen dave.hansen@linux.intel.com To: stable@vger.kernel.org
Signed-off-by: Pawan Gupta pawan.kumar.gupta@linux.intel.com --- Pawan Gupta (5): x86/bugs: Add asm helpers for executing VERW x86/entry_64: Add VERW just before userspace transition x86/entry_32: Add VERW just before userspace transition x86/bugs: Use ALTERNATIVE() instead of mds_user_clear static key KVM/VMX: Move VERW closer to VMentry for MDS mitigation
Sean Christopherson (1): KVM/VMX: Use BT+JNC, i.e. EFLAGS.CF to select VMRESUME vs. VMLAUNCH
Documentation/arch/x86/mds.rst | 38 +++++++++++++++++++++++++----------- arch/x86/entry/entry.S | 23 ++++++++++++++++++++++ arch/x86/entry/entry_32.S | 3 +++ arch/x86/entry/entry_64.S | 11 +++++++++++ arch/x86/entry/entry_64_compat.S | 1 + arch/x86/include/asm/cpufeatures.h | 2 +- arch/x86/include/asm/entry-common.h | 1 - arch/x86/include/asm/nospec-branch.h | 25 ++++++++++++------------ arch/x86/kernel/cpu/bugs.c | 15 ++++++-------- arch/x86/kernel/nmi.c | 3 --- arch/x86/kvm/vmx/run_flags.h | 7 +++++-- arch/x86/kvm/vmx/vmenter.S | 9 ++++++--- arch/x86/kvm/vmx/vmx.c | 20 +++++++++++++++---- 13 files changed, 112 insertions(+), 46 deletions(-) --- base-commit: d8a27ea2c98685cdaa5fa66c809c7069a4ff394b change-id: 20240226-delay-verw-backport-6-6-y-2cda3298e600