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Date: Mon, 21 Mar 2022 16:48:44 -0700
From: Ben Gardon <bgardon@...gle.com>
To: linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc: Paolo Bonzini <pbonzini@...hat.com>, Peter Xu <peterx@...hat.com>,
Sean Christopherson <seanjc@...gle.com>,
David Matlack <dmatlack@...gle.com>,
Jim Mattson <jmattson@...gle.com>,
David Dunn <daviddunn@...gle.com>,
Jing Zhang <jingzhangos@...gle.com>,
Junaid Shahid <junaids@...gle.com>,
Ben Gardon <bgardon@...gle.com>
Subject: [PATCH v2 11/11] KVM: x86/MMU: Require reboot permission to disable
NX hugepages
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 <jmattson@...gle.com>
Signed-off-by: Ben Gardon <bgardon@...gle.com>
---
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
--
2.35.1.894.gb6a874cedc-goog
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