v2: - Runtime patch jmp instead of verw in macro CLEAR_CPU_BUFFERS due to lack of relative addressing support in relocations in kernels <v6.5. - Rebased to v6.1.80 - Boot tested with KASLR and KPTI enabled. - Fixed warning: arch/x86/entry/entry.o: warning: objtool: mds_verw_sel+0x0: unreachable instruction - Verified VERW being executed with mitigation ON, and not being executed with mitigation turned OFF. - Rebased to v6.1.80. v1: https://lore.kernel.org/r/20240226-delay-verw-backport-6-1-y-v1-0-b3a2c5b9b0cb@xxxxxxxxxxxxxxx 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@tip-bot2/ Patch 1,2,5 and 6 needed conflict resolution. I saw a few new warnings: arch/x86/entry/entry.o: warning: objtool: mds_verw_sel+0x0: unreachable instruction I tried using REACHABLE, but that did not fix the warning. For the below warning: vmlinux.o: warning: objtool: .altinstr_replacement+0x17: unsupported relocation in alternatives section not sure if this is related to this series or a pre-existing warning, I will check later without this series. I am not too concerned because the alternative did substitute verw correctly: entry_SYSCALL_64: ... 0xffffffff8200013d <+253>: swapgs 0xffffffff82000140 <+256>: verw 0xffffffff82000000 0xffffffff82000148 <+264>: sysretq 0xffffffff8200014b <+267>: int3 Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> To: stable@xxxxxxxxxxxxxxx Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx> --- 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/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 | 27 +++++++++++++------------ 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 | 12 ++++++++---- 13 files changed, 106 insertions(+), 46 deletions(-) --- base-commit: a3eb3a74aa8c94e6c8130b55f3b031f29162868c change-id: 20240226-delay-verw-backport-6-1-y-4b0cec84087c Best regards, -- Thanks, Pawan
