From 13d1c5b17d127afbd947210c5cdd80eaded5d9f4 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Wed, 6 Jun 2018 17:38:09 +0200 Subject: kvm: x86: use correct privilege level for sgdt/sidt/fxsave/fxrstor access commit 3c9fa24ca7c9c47605672916491f79e8ccacb9e6 upstream. The functions that were used in the emulation of fxrstor, fxsave, sgdt and sidt were originally meant for task switching, and as such they did not check privilege levels. This is very bad when the same functions are used in the emulation of unprivileged instructions. This is CVE-2018-10853. The obvious fix is to add a new argument to ops->read_std and ops->write_std, which decides whether the access is a "system" access or should use the processor's CPL. Fixes: 129a72a0d3c8 ("KVM: x86: Introduce segmented_write_std", 2017-01-12) Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/x86.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) (limited to 'arch/x86/kvm/x86.c') diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 95d2709879f3..5ca23af44c81 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4408,10 +4408,15 @@ EXPORT_SYMBOL_GPL(kvm_read_guest_virt); static int emulator_read_std(struct x86_emulate_ctxt *ctxt, gva_t addr, void *val, unsigned int bytes, - struct x86_exception *exception) + struct x86_exception *exception, bool system) { struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt); - return kvm_read_guest_virt_helper(addr, val, bytes, vcpu, 0, exception); + u32 access = 0; + + if (!system && kvm_x86_ops->get_cpl(vcpu) == 3) + access |= PFERR_USER_MASK; + + return kvm_read_guest_virt_helper(addr, val, bytes, vcpu, access, exception); } static int kvm_read_guest_phys_system(struct x86_emulate_ctxt *ctxt, @@ -4455,12 +4460,17 @@ out: } static int emulator_write_std(struct x86_emulate_ctxt *ctxt, gva_t addr, void *val, - unsigned int bytes, struct x86_exception *exception) + unsigned int bytes, struct x86_exception *exception, + bool system) { struct kvm_vcpu *vcpu = emul_to_vcpu(ctxt); + u32 access = PFERR_WRITE_MASK; + + if (!system && kvm_x86_ops->get_cpl(vcpu) == 3) + access |= PFERR_USER_MASK; return kvm_write_guest_virt_helper(addr, val, bytes, vcpu, - PFERR_WRITE_MASK, exception); + access, exception); } int kvm_write_guest_virt_system(struct kvm_vcpu *vcpu, gva_t addr, void *val, -- cgit v1.2.3