Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751563AbdIOXTx (ORCPT ); Fri, 15 Sep 2017 19:19:53 -0400 Received: from mail-wm0-f51.google.com ([74.125.82.51]:46208 "EHLO mail-wm0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751211AbdIOXTu (ORCPT ); Fri, 15 Sep 2017 19:19:50 -0400 X-Google-Smtp-Source: AOwi7QC+eA7fZQ36bP2eqr1DnXy0oPC+t6GmSc8TQ7Rt+kbLNjdGVnlD/LCzoPei9d7RtVb9fz1YeSc0EhNGqc4N5PE= MIME-Version: 1.0 In-Reply-To: <1503577676-12345-3-git-send-email-yu.c.zhang@linux.intel.com> References: <1503577676-12345-1-git-send-email-yu.c.zhang@linux.intel.com> <1503577676-12345-3-git-send-email-yu.c.zhang@linux.intel.com> From: Jim Mattson Date: Fri, 15 Sep 2017 16:19:48 -0700 Message-ID: Subject: Re: [PATCH v3 2/5] KVM: MMU: check guest CR3 reserved bits based on its physical address width. To: Yu Zhang Cc: kvm list , LKML , Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Thomas Gleixner , Ingo Molnar , "H . Peter Anvin" , xiaoguangrong@tencent.com, Joerg Roedel Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4119 Lines: 120 On Thu, Aug 24, 2017 at 5:27 AM, Yu Zhang wrote: > Currently, KVM uses CR3_L_MODE_RESERVED_BITS to check the > reserved bits in CR3. Yet the length of reserved bits in > guest CR3 should be based on the physical address width > exposed to the VM. This patch changes CR3 check logic to > calculate the reserved bits at runtime. > > Signed-off-by: Yu Zhang > --- > arch/x86/include/asm/kvm_host.h | 1 - > arch/x86/kvm/emulate.c | 14 ++++++++++++-- > arch/x86/kvm/mmu.h | 3 +++ > arch/x86/kvm/x86.c | 8 ++++---- > 4 files changed, 19 insertions(+), 7 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 6db0ed9..e716228 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -79,7 +79,6 @@ > | X86_CR0_ET | X86_CR0_NE | X86_CR0_WP | X86_CR0_AM \ > | X86_CR0_NW | X86_CR0_CD | X86_CR0_PG)) > > -#define CR3_L_MODE_RESERVED_BITS 0xFFFFFF0000000000ULL > #define CR3_PCID_INVD BIT_64(63) > #define CR4_RESERVED_BITS \ > (~(unsigned long)(X86_CR4_VME | X86_CR4_PVI | X86_CR4_TSD | X86_CR4_DE\ > diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c > index 319d91f..a89b595 100644 > --- a/arch/x86/kvm/emulate.c > +++ b/arch/x86/kvm/emulate.c > @@ -28,6 +28,7 @@ > > #include "x86.h" > #include "tss.h" > +#include "mmu.h" > > /* > * Operand types > @@ -4097,8 +4098,17 @@ static int check_cr_write(struct x86_emulate_ctxt *ctxt) > u64 rsvd = 0; > > ctxt->ops->get_msr(ctxt, MSR_EFER, &efer); > - if (efer & EFER_LMA) > - rsvd = CR3_L_MODE_RESERVED_BITS & ~CR3_PCID_INVD; > + if (efer & EFER_LMA) { > + u64 maxphyaddr; > + u32 eax = 0x80000008; > + > + if (ctxt->ops->get_cpuid(ctxt, &eax, NULL, NULL, > + NULL, false)) Passing NULL for the address of ecx looks problematic to me. We have: static bool emulator_get_cpuid(struct x86_emulate_ctxt *ctxt, u32 *eax, u32 *ebx, u32 *ecx, u32 *edx, bool check_limit) { return kvm_cpuid(emul_to_vcpu(ctxt), eax, ebx, ecx, edx, check_limit); } And: bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx, u32 *ecx, u32 *edx, bool check_limit) { u32 function = *eax, index = *ecx; struct kvm_cpuid_entry2 *best; bool entry_found = true; ... Doesn't this immediately try to dereference a NULL pointer? How much testing have you done of this code? > + maxphyaddr = eax & 0xff; > + else > + maxphyaddr = 36; > + rsvd = rsvd_bits(maxphyaddr, 62); > + } > > if (new_val & rsvd) > return emulate_gp(ctxt, 0); > diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h > index 3ed6192..67e7ec2 100644 > --- a/arch/x86/kvm/mmu.h > +++ b/arch/x86/kvm/mmu.h > @@ -48,6 +48,9 @@ > > static inline u64 rsvd_bits(int s, int e) > { > + if (e < s) > + return 0; > + > return ((1ULL << (e - s + 1)) - 1) << s; > } > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index cc2c7e4..79f5889 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -813,10 +813,10 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3) > return 0; > } > > - if (is_long_mode(vcpu)) { > - if (cr3 & CR3_L_MODE_RESERVED_BITS) > - return 1; > - } else if (is_pae(vcpu) && is_paging(vcpu) && > + if (is_long_mode(vcpu) && > + (cr3 & rsvd_bits(cpuid_maxphyaddr(vcpu), 62))) > + return 1; > + else if (is_pae(vcpu) && is_paging(vcpu) && > !load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3)) > return 1; > > -- > 2.5.0 >