If split lock detect is enabled (warn/fatal), #AC handler calls die() when split lock happens in kernel. Malicous guest can exploit the KVM emulator to trigger split lock #AC in kernel[1]. So just emulating the access as a write if it's a split-lock access (the same as access spans page) to avoid malicious attacking kernel. More discussion can be found [2][3]. [1] https://lore.kernel.org/lkml/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> --- arch/x86/kvm/x86.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 5de200663f51..1a0e6c0b1b39 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -5873,6 +5873,7 @@ 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 = PAGE_MASK; gpa_t gpa; char *kaddr; bool exchanged; @@ -5887,7 +5888,11 @@ 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)) + if (split_lock_detect_on()) + page_line_mask = ~(cache_line_size() - 1); + + /* when write spans page or spans cache when SLD enabled */ + if (((gpa + bytes - 1) & page_line_mask) != (gpa & page_line_mask)) goto emul_write; if (kvm_vcpu_map(vcpu, gpa_to_gfn(gpa), &map)) -- 2.20.1
