From patchwork Mon Mar 21 23:48:44 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ben Gardon X-Patchwork-Id: 12787958 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 603B6C433FE for ; Mon, 21 Mar 2022 23:49:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233687AbiCUXvW (ORCPT ); Mon, 21 Mar 2022 19:51:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59824 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233692AbiCUXvO (ORCPT ); Mon, 21 Mar 2022 19:51:14 -0400 Received: from mail-pl1-x64a.google.com (mail-pl1-x64a.google.com [IPv6:2607:f8b0:4864:20::64a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AC020195D8A for ; Mon, 21 Mar 2022 16:49:21 -0700 (PDT) Received: by mail-pl1-x64a.google.com with SMTP id j1-20020a170903028100b0014b1f9e0068so6234635plr.8 for ; Mon, 21 Mar 2022 16:49:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=m5T3Hbrl4DyDMOn7A4MiOSbjCSgOB5xSxPj2asSn9Wg=; b=Zacml26OoL/GF6NlL2gXG5FXZUDRoVGueOLiN6hKDPI9ASu/bkCxXaoxGt8/F0Mh5J FWAq8pUohHlkR4XmRKhyQX+XZq5v4u5JIPCUzw9V+zwzW3CD09XBZejqxuTyU+Ii6p5B h+Y6Mgnp/2n0gVU4Y4TPVDo9iP7NTj1BSTk5eHfqbtDS08cJpEdPHNTIFJhzeaylgWGK HCBBpc9KmVs32VdzG55JHsK/Ub+SjtOb9RQrJSwQiVk1whsye2wBJCWaosKcrBzNQroP kwSzod88EmWiLZ9h8zLQyjncwJB9lHtFgRayQOIFH24ZZj+dulNmO9RI7Mi8JwBXLPiG qoOQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=m5T3Hbrl4DyDMOn7A4MiOSbjCSgOB5xSxPj2asSn9Wg=; b=xnmpUA7Zoq44nbrOgqOqycBJOTwyfaPOt6d8gzFbP1LHgJtunIoYnMDUDZ7ywt98kI NMSxDWbYYleEbHQ0fE9O92rcfI0IXSXw4gqKYSgy/kYbngg7avvMoPb/EbZmTf/ajR8Z HEfACHSlAqCL5LeLKSTDdXF5gGuWAlvj4YyfEn2CNEMsv4NYJ8LKmd844nYKj05IhDZ+ okxTvAUkyq3yTRN8ISF7bXKQqQfRPscD70KArAueLRjbPOfpr6zEYjTL3zyZ7uonuZDq w4Dz/LPVNRpgyJr664rp+Ee2EI6ZJBmJiE+OONse1LKivwwSmHxX9fJ4HVgpsFvvxL90 UtvQ== X-Gm-Message-State: AOAM530mIclMN0y+KryagLprVLitxo/LxuIT6S4wX7yQqg4gAO4aUBJx V4vCYVTQR+5PM4foi6ROrS7vVuoJOnaZ X-Google-Smtp-Source: ABdhPJxiNgqjZsgRsl/JaT3z6xvFFNLrDtQigGPFZbUOauwKxglp+Z1PfpkQGMLQS016z4FSanVYNBEijQ/w X-Received: from bgardon.sea.corp.google.com ([2620:15c:100:202:b76a:f152:cb5e:5cd2]) (user=bgardon job=sendgmr) by 2002:a17:90b:e81:b0:1c6:5a9c:5afa with SMTP id fv1-20020a17090b0e8100b001c65a9c5afamr204556pjb.1.1647906560754; Mon, 21 Mar 2022 16:49:20 -0700 (PDT) Date: Mon, 21 Mar 2022 16:48:44 -0700 In-Reply-To: <20220321234844.1543161-1-bgardon@google.com> Message-Id: <20220321234844.1543161-12-bgardon@google.com> Mime-Version: 1.0 References: <20220321234844.1543161-1-bgardon@google.com> X-Mailer: git-send-email 2.35.1.894.gb6a874cedc-goog Subject: [PATCH v2 11/11] KVM: x86/MMU: Require reboot permission to disable NX hugepages From: Ben Gardon To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Paolo Bonzini , Peter Xu , Sean Christopherson , David Matlack , Jim Mattson , David Dunn , Jing Zhang , Junaid Shahid , Ben Gardon Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Ensure that the userspace actor attempting to disable NX hugepages has permission to reboot the system. Since disabling NX hugepages would allow a guest to crash the system, it is similar to reboot permissions. This approach is the simplest permission gating, but passing a file descriptor opened for write for the module parameter would also work well and be more precise. The latter approach was suggested by Sean Christopherson. Suggested-by: Jim Mattson Signed-off-by: Ben Gardon --- arch/x86/kvm/x86.c | 18 ++++++- .../selftests/kvm/include/kvm_util_base.h | 2 + tools/testing/selftests/kvm/lib/kvm_util.c | 7 +++ .../selftests/kvm/x86_64/nx_huge_pages_test.c | 49 ++++++++++++++----- .../kvm/x86_64/nx_huge_pages_test.sh | 2 +- 5 files changed, 65 insertions(+), 13 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 74351cbb9b5b..995f30667619 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -4256,7 +4256,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) case KVM_CAP_SYS_ATTRIBUTES: case KVM_CAP_VAPIC: case KVM_CAP_ENABLE_CAP: - case KVM_CAP_VM_DISABLE_NX_HUGE_PAGES: r = 1; break; case KVM_CAP_EXIT_HYPERCALL: @@ -4359,6 +4358,14 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) case KVM_CAP_DISABLE_QUIRKS2: r = KVM_X86_VALID_QUIRKS; break; + case KVM_CAP_VM_DISABLE_NX_HUGE_PAGES: + /* + * Since the risk of disabling NX hugepages is a guest crashing + * the system, ensure the userspace process has permission to + * reboot the system. + */ + r = capable(CAP_SYS_BOOT); + break; default: break; } @@ -6050,6 +6057,15 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, mutex_unlock(&kvm->lock); break; case KVM_CAP_VM_DISABLE_NX_HUGE_PAGES: + /* + * Since the risk of disabling NX hugepages is a guest crashing + * the system, ensure the userspace process has permission to + * reboot the system. + */ + if (!capable(CAP_SYS_BOOT)) { + r = -EPERM; + break; + } kvm->arch.disable_nx_huge_pages = true; kvm_update_nx_huge_pages(kvm); r = 0; diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h index 72163ba2f878..4db8251c3ce5 100644 --- a/tools/testing/selftests/kvm/include/kvm_util_base.h +++ b/tools/testing/selftests/kvm/include/kvm_util_base.h @@ -411,4 +411,6 @@ uint64_t vm_get_single_stat(struct kvm_vm *vm, const char *stat_name); uint32_t guest_get_vcpuid(void); +void vm_disable_nx_huge_pages(struct kvm_vm *vm); + #endif /* SELFTEST_KVM_UTIL_BASE_H */ diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c index 9d72d1bb34fa..46a7fa08d3e0 100644 --- a/tools/testing/selftests/kvm/lib/kvm_util.c +++ b/tools/testing/selftests/kvm/lib/kvm_util.c @@ -2765,3 +2765,10 @@ uint64_t vm_get_single_stat(struct kvm_vm *vm, const char *stat_name) return value; } +void vm_disable_nx_huge_pages(struct kvm_vm *vm) +{ + struct kvm_enable_cap cap = { 0 }; + + cap.cap = KVM_CAP_VM_DISABLE_NX_HUGE_PAGES; + vm_enable_cap(vm, &cap); +} diff --git a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c index 2bcbe4efdc6a..5ce98f759bc8 100644 --- a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c +++ b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.c @@ -57,13 +57,40 @@ static void check_split_count(struct kvm_vm *vm, int expected_splits) expected_splits, actual_splits); } +static void help(void) +{ + puts(""); + printf("usage: nx_huge_pages_test.sh [-x]\n"); + puts(""); + printf(" -x: Allow executable huge pages on the VM.\n"); + puts(""); + exit(0); +} + int main(int argc, char **argv) { struct kvm_vm *vm; struct timespec ts; + bool disable_nx = false; + int opt; + + while ((opt = getopt(argc, argv, "x")) != -1) { + switch (opt) { + case 'x': + disable_nx = true; + break; + case 'h': + default: + help(); + break; + } + } vm = vm_create(VM_MODE_DEFAULT, DEFAULT_GUEST_PHY_PAGES, O_RDWR); + if (disable_nx) + vm_disable_nx_huge_pages(vm); + vm_userspace_mem_region_add(vm, VM_MEM_SRC_ANONYMOUS_HUGETLB, HPAGE_PADDR_START, HPAGE_SLOT, HPAGE_SLOT_NPAGES, 0); @@ -83,21 +110,21 @@ int main(int argc, char **argv) * at 2M. */ run_guest_code(vm, guest_code0); - check_2m_page_count(vm, 2); - check_split_count(vm, 2); + check_2m_page_count(vm, disable_nx ? 4 : 2); + check_split_count(vm, disable_nx ? 0 : 2); /* * guest_code1 is in the same huge page as data1, so it will cause * that huge page to be remapped at 4k. */ run_guest_code(vm, guest_code1); - check_2m_page_count(vm, 1); - check_split_count(vm, 3); + check_2m_page_count(vm, disable_nx ? 4 : 1); + check_split_count(vm, disable_nx ? 0 : 3); /* Run guest_code0 again to check that is has no effect. */ run_guest_code(vm, guest_code0); - check_2m_page_count(vm, 1); - check_split_count(vm, 3); + check_2m_page_count(vm, disable_nx ? 4 : 1); + check_split_count(vm, disable_nx ? 0 : 3); /* * Give recovery thread time to run. The wrapper script sets @@ -110,7 +137,7 @@ int main(int argc, char **argv) /* * Now that the reclaimer has run, all the split pages should be gone. */ - check_2m_page_count(vm, 1); + check_2m_page_count(vm, disable_nx ? 4 : 1); check_split_count(vm, 0); /* @@ -118,13 +145,13 @@ int main(int argc, char **argv) * again to check that pages are mapped at 2M again. */ run_guest_code(vm, guest_code0); - check_2m_page_count(vm, 2); - check_split_count(vm, 2); + check_2m_page_count(vm, disable_nx ? 4 : 2); + check_split_count(vm, disable_nx ? 0 : 2); /* Pages are once again split from running guest_code1. */ run_guest_code(vm, guest_code1); - check_2m_page_count(vm, 1); - check_split_count(vm, 3); + check_2m_page_count(vm, disable_nx ? 4 : 1); + check_split_count(vm, disable_nx ? 0 : 3); kvm_vm_free(vm); diff --git a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh index 19fc95723fcb..29f999f48848 100755 --- a/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh +++ b/tools/testing/selftests/kvm/x86_64/nx_huge_pages_test.sh @@ -14,7 +14,7 @@ echo 1 > /sys/module/kvm/parameters/nx_huge_pages_recovery_ratio echo 100 > /sys/module/kvm/parameters/nx_huge_pages_recovery_period_ms echo 200 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages -./nx_huge_pages_test +./nx_huge_pages_test "${@}" RET=$? echo $NX_HUGE_PAGES > /sys/module/kvm/parameters/nx_huge_pages