On Wed, Jun 26, 2024 at 01:08:47PM -0700, Sean Christopherson wrote: > On Tue, Jun 25, 2024, Pei Li wrote: > > Check for invalid hva address stored in data before calling > > kvm_gpc_activate_hva() instead of only compare with 0. > > > > Reported-by: syzbot+fd555292a1da3180fc82@xxxxxxxxxxxxxxxxxxxxxxxxx > > Closes: https://syzkaller.appspot.com/bug?extid=fd555292a1da3180fc82 > > Tested-by: syzbot+fd555292a1da3180fc82@xxxxxxxxxxxxxxxxxxxxxxxxx > > Signed-off-by: Pei Li <peili.dev@xxxxxxxxx> > > --- > > Syzbot reports a warning message in __kvm_gpc_refresh(). This warning > > requires at least one of gpa and uhva to be valid. > > WARNING: CPU: 0 PID: 5090 at arch/x86/kvm/../../../virt/kvm/pfncache.c:259 __kvm_gpc_refresh+0xf17/0x1090 arch/x86/kvm/../../../virt/kvm/pfncache.c:259 > > > > We are calling it from kvm_gpc_activate_hva(). This function always calls > > __kvm_gpc_activate() with INVALID_GPA. Thus, uhva must be valid to > > disable this warning. > > > > This patch checks for invalid hva address as well instead of only > > comparing hva with 0 before calling kvm_gpc_activate_hva() > > > > syzbot has tested the proposed patch and the reproducer did not trigger > > any issue. > > > > Tested on: > > > > commit: 55027e68 Merge tag 'input-for-v6.10-rc5' of git://git... > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=16ea803a980000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=e40800950091403a > > dashboard link: https://syzkaller.appspot.com/bug?extid=fd555292a1da3180fc82 > > compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40 > > patch: https://syzkaller.appspot.com/x/patch.diff?x=16eeb53e980000 > > > > Note: testing is done by a robot and is best-effort only. > > --- > > arch/x86/kvm/xen.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c > > index f65b35a05d91..de5f34492405 100644 > > --- a/arch/x86/kvm/xen.c > > +++ b/arch/x86/kvm/xen.c > > @@ -881,7 +881,7 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data) > > r = kvm_gpc_activate(&vcpu->arch.xen.vcpu_info_cache, > > data->u.gpa, sizeof(struct vcpu_info)); > > } else { > > - if (data->u.hva == 0) { > > + if (data->u.hva == 0 || kvm_is_error_hva(data->u.hva)) { > > kvm_gpc_deactivate(&vcpu->arch.xen.vcpu_info_cache); > > r = 0; > > break; > > Hmm, I think what we want is to return -EINVAL in this case, not deactivate the > region. I could have sworn KVM does that. Gah, I caught > KVM_XEN_ATTR_TYPE_SHARED_INFO_HVA during review, but missed this one. So to fix > this immediate bug, and avoid similar issues in the future, this? > > diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c > index 93814d3850eb..622fe24da910 100644 > --- a/arch/x86/kvm/xen.c > +++ b/arch/x86/kvm/xen.c > @@ -741,7 +741,7 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data) > } else { > void __user * hva = u64_to_user_ptr(data->u.shared_info.hva); > > - if (!PAGE_ALIGNED(hva) || !access_ok(hva, PAGE_SIZE)) { > + if (!PAGE_ALIGNED(hva)) { > r = -EINVAL; > } else if (!hva) { > kvm_gpc_deactivate(&kvm->arch.xen.shinfo_cache); > diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c > index 0ab90f45db37..728d2c1b488a 100644 > --- a/virt/kvm/pfncache.c > +++ b/virt/kvm/pfncache.c > @@ -438,6 +438,9 @@ int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long len) > > int kvm_gpc_activate_hva(struct gfn_to_pfn_cache *gpc, unsigned long uhva, unsigned long len) > { > + if (!access_ok((void __user *)uhva, len)) > + return -EINVAL; > + > return __kvm_gpc_activate(gpc, INVALID_GPA, uhva, len); > } > Thanks Sean. I’ll test and work on v2 based on your suggestions. Best regards, Pei
