From: Eugene Korenevsky Date: Wed, 5 Jun 2019 21:17:39 +0000 (+0300) Subject: kvm: vmx: fix limit checking in get_vmx_mem_address() X-Git-Tag: v5.3-rc1~115^2~87 X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=c1a9acbc5295e278d788e9f7510f543bc9864fa2;p=linux.git kvm: vmx: fix limit checking in get_vmx_mem_address() Intel SDM vol. 3, 5.3: The processor causes a general-protection exception (or, if the segment is SS, a stack-fault exception) any time an attempt is made to access the following addresses in a segment: - A byte at an offset greater than the effective limit - A word at an offset greater than the (effective-limit – 1) - A doubleword at an offset greater than the (effective-limit – 3) - A quadword at an offset greater than the (effective-limit – 7) Therefore, the generic limit checking error condition must be exn = (off > limit + 1 - access_len) = (off + access_len - 1 > limit) but not exn = (off + access_len > limit) as for now. Also avoid integer overflow of `off` at 32-bit KVM by casting it to u64. Note: access length is currently sizeof(u64) which is incorrect. This will be fixed in the subsequent patch. Signed-off-by: Eugene Korenevsky Signed-off-by: Paolo Bonzini --- diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c index 0f705c7d590c..018790c1b47f 100644 --- a/arch/x86/kvm/vmx/nested.c +++ b/arch/x86/kvm/vmx/nested.c @@ -4115,7 +4115,7 @@ int get_vmx_mem_address(struct kvm_vcpu *vcpu, unsigned long exit_qualification, */ if (!(s.base == 0 && s.limit == 0xffffffff && ((s.type & 8) || !(s.type & 4)))) - exn = exn || (off + sizeof(u64) > s.limit); + exn = exn || ((u64)off + sizeof(u64) - 1 > s.limit); } if (exn) { kvm_queue_exception_e(vcpu,