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Peter Anvin" , linux-kernel@vger.kernel.org, Emanuele Giuseppe Esposito Subject: [PATCH v5 0/7] KVM: nSVM: avoid TOC/TOU race when checking vmcb12 Date: Wed, 3 Nov 2021 10:05:20 -0400 Message-Id: <20211103140527.752797-1-eesposit@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently there is a TOC/TOU race between the check of vmcb12's efer, cr0 and cr4 registers and the later save of their values in svm_set_*, because the guest could modify the values in the meanwhile. To solve this issue, this series introduces and uses svm->nested.save structure in enter_svm_guest_mode to save the current value of efer, cr0 and cr4 and later use these to set the vcpu->arch.* state. Similarly, svm->nested.ctl contains fields that are not used, so having a full vmcb_control_area means passing uninitialized fields. Patches 1,3 and 8 take care of renaming and refactoring code. Patches 2 and 6 introduce respectively vmcb_ctrl_area_cached and vmcb_save_area_cached. Patches 4 and 5 use vmcb_save_area_cached to avoid TOC/TOU, and patch 7 uses vmcb_ctrl_area_cached. Signed-off-by: Emanuele Giuseppe Esposito --- v5: * rebased on kvm/queue branch v4: * introduce _* helpers (_nested_vmcb_check_save, _nested_copy_vmcb_control_to_cache, _nested_copy_vmcb_save_to_cache) that take care of additional parameters. * svm_set_nested_state: introduce {save, ctl}_cached variables to not pollute svm->nested.{save,ctl} state, especially if the check fails. remove also unnecessary memset added in previous versions. * svm_get_nested_state: change stack variable ctl introduced in this series into a pointer that will be zeroed and freed after it has been copied to user v3: * merge this series with "KVM: nSVM: use vmcb_ctrl_area_cached instead of vmcb_control_area in nested state" * rename "nested_load_save_from_vmcb12" in "nested_copy_vmcb_save_to_cache" * rename "nested_load_control_from_vmcb12" in "nested_copy_vmcb_control_to_cache" * change check functions (nested_vmcb_valid_sregs and nested_vmcb_valid_sregs) to accept only the vcpu parameter, since we only check nested state now * rename "vmcb_is_intercept_cached" in "vmcb12_is_intercept" and duplicate the implementation instead of calling vmcb_is_intercept v2: * svm->nested.save is a separate struct vmcb_save_area_cached, and not vmcb_save_area. * update also vmcb02->cr3 with svm->nested.save.cr3 RFC: * use svm->nested.save instead of local variables. * not dependent anymore from "KVM: nSVM: remove useless kvm_clear_*_queue" * simplified patches, we just use the struct and not move the check nearer to the TOU. Emanuele Giuseppe Esposito (7): KVM: nSVM: move nested_vmcb_check_cr3_cr4 logic in nested_vmcb_valid_sregs nSVM: introduce smv->nested.save to cache save area fields nSVM: rename nested_load_control_from_vmcb12 in nested_copy_vmcb_control_to_cache nSVM: use vmcb_save_area_cached in nested_vmcb_valid_sregs() nSVM: use svm->nested.save to load vmcb12 registers and avoid TOC/TOU races nSVM: introduce struct vmcb_ctrl_area_cached nSVM: use vmcb_ctrl_area_cached instead of vmcb_control_area in struct svm_nested_state arch/x86/kvm/svm/nested.c | 250 ++++++++++++++++++++++++-------------- arch/x86/kvm/svm/svm.c | 7 +- arch/x86/kvm/svm/svm.h | 59 ++++++++- 3 files changed, 213 insertions(+), 103 deletions(-) -- 2.27.0