From: Xiaoyao Li <xiaoyao.li@xxxxxxxxx> Emulate split-lock accesses as writes if split lock detection is on to avoid #AC during emulation, which will result in a panic(). This should never occur for a well behaved guest, but a malicious guest can manipulate the TLB to trigger emulation of a locked instruction[1]. More discussion can be found [2][3]. [1] https://lkml.kernel.org/r/8c5b11c9-58df-38e7-a514-dc12d687b198@xxxxxxxxxx [2] https://lkml.kernel.org/r/20200131200134.GD18946@xxxxxxxxxxxxxxx [3] https://lkml.kernel.org/r/20200227001117.GX9940@xxxxxxxxxxxxxxx Suggested-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx> Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx> --- arch/x86/kvm/x86.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index bf8564d73fc3..37ce0fc9a62d 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -5875,6 +5875,7 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt, { struct kvm_host_map map; struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt); + u64 page_line_mask; gpa_t gpa; char *kaddr; bool exchanged; @@ -5889,7 +5890,16 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt, (gpa & PAGE_MASK) == APIC_DEFAULT_PHYS_BASE) goto emul_write; - if (((gpa + bytes - 1) & PAGE_MASK) != (gpa & PAGE_MASK)) + /* + * Emulate the atomic as a straight write to avoid #AC if SLD is + * enabled in the host and the access splits a cache line. + */ + if (boot_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT)) + page_line_mask = ~(cache_line_size() - 1); + else + page_line_mask = PAGE_MASK; + + if (((gpa + bytes - 1) & page_line_mask) != (gpa & page_line_mask)) goto emul_write; if (kvm_vcpu_map(vcpu, gpa_to_gfn(gpa), &map)) -- 2.24.1
