ptp: kvm: Use decrypted memory in confidential guest on x86

KVM_HC_CLOCK_PAIRING currently fails inside SEV-SNP guests because the
guest passes an address to static data to the host. In confidential
computing the host can't access arbitrary guest memory so handling the
hypercall runs into an "rmpfault". To make the hypercall work, the guest
needs to explicitly mark the memory as decrypted. Do that in
kvm_arch_ptp_init(), but retain the previous behavior for
non-confidential guests to save us from having to allocate memory.

Add a new arch-specific function (kvm_arch_ptp_exit()) to free the
allocation and mark the memory as encrypted again.

Signed-off-by: Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>
Link: https://lore.kernel.org/r/20230308150531.477741-1-jpiotrowski@linux.microsoft.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/ptp/ptp_kvm_arm.c b/drivers/ptp/ptp_kvm_arm.c
index b7d28c8dfb84e37df45f2dc4def7c2c11e1efa08..e68e6943167beb448b0aca75665236ff8314773e 100644 (file)
--- a/drivers/ptp/ptp_kvm_arm.c
+++ b/drivers/ptp/ptp_kvm_arm.c
@@ -22,6 +22,10 @@ int kvm_arch_ptp_init(void)
        return 0;
 }
 
+void kvm_arch_ptp_exit(void)
+{
+}
+
 int kvm_arch_ptp_get_clock(struct timespec64 *ts)
 {
        return kvm_arch_ptp_get_crosststamp(NULL, ts, NULL);

diff --git a/drivers/ptp/ptp_kvm_common.c b/drivers/ptp/ptp_kvm_common.c
index 9141162c423795c3f45f8c4c1a36aee82b47c9bc..2418977989beb420a9587d9c013e61b950d09b85 100644 (file)
--- a/drivers/ptp/ptp_kvm_common.c
+++ b/drivers/ptp/ptp_kvm_common.c
@@ -130,6 +130,7 @@ static struct kvm_ptp_clock kvm_ptp_clock;
 static void __exit ptp_kvm_exit(void)
 {
        ptp_clock_unregister(kvm_ptp_clock.ptp_clock);
+       kvm_arch_ptp_exit();
 }
 
 static int __init ptp_kvm_init(void)

diff --git a/drivers/ptp/ptp_kvm_x86.c b/drivers/ptp/ptp_kvm_x86.c
index 4991054a213506601a24a515418223ee278dd448..902844cc1a17d5bd46461702ea149c852454db46 100644 (file)
--- a/drivers/ptp/ptp_kvm_x86.c
+++ b/drivers/ptp/ptp_kvm_x86.c
@@ -14,27 +14,64 @@
 #include <uapi/linux/kvm_para.h>
 #include <linux/ptp_clock_kernel.h>
 #include <linux/ptp_kvm.h>
+#include <linux/set_memory.h>
 
 static phys_addr_t clock_pair_gpa;
-static struct kvm_clock_pairing clock_pair;
+static struct kvm_clock_pairing clock_pair_glbl;
+static struct kvm_clock_pairing *clock_pair;
 
 int kvm_arch_ptp_init(void)
 {
+       struct page *p;
        long ret;
 
        if (!kvm_para_available())
                return -ENODEV;
 
-       clock_pair_gpa = slow_virt_to_phys(&clock_pair);
-       if (!pvclock_get_pvti_cpu0_va())
-               return -ENODEV;
+       if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) {
+               p = alloc_page(GFP_KERNEL | __GFP_ZERO);
+               if (!p)
+                       return -ENOMEM;
+
+               clock_pair = page_address(p);
+               ret = set_memory_decrypted((unsigned long)clock_pair, 1);
+               if (ret) {
+                       __free_page(p);
+                       clock_pair = NULL;
+                       goto nofree;
+               }
+       } else {
+               clock_pair = &clock_pair_glbl;
+       }
+
+       clock_pair_gpa = slow_virt_to_phys(clock_pair);
+       if (!pvclock_get_pvti_cpu0_va()) {
+               ret = -ENODEV;
+               goto err;
+       }
 
        ret = kvm_hypercall2(KVM_HC_CLOCK_PAIRING, clock_pair_gpa,
                             KVM_CLOCK_PAIRING_WALLCLOCK);
-       if (ret == -KVM_ENOSYS)
-               return -ENODEV;
+       if (ret == -KVM_ENOSYS) {
+               ret = -ENODEV;
+               goto err;
+       }
 
        return ret;
+
+err:
+       kvm_arch_ptp_exit();
+nofree:
+       return ret;
+}
+
+void kvm_arch_ptp_exit(void)
+{
+       if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) {
+               WARN_ON(set_memory_encrypted((unsigned long)clock_pair, 1));
+               free_page((unsigned long)clock_pair);
+               clock_pair = NULL;
+       }
 }
 
 int kvm_arch_ptp_get_clock(struct timespec64 *ts)
@@ -49,8 +86,8 @@ int kvm_arch_ptp_get_clock(struct timespec64 *ts)
                return -EOPNOTSUPP;
        }
 
-       ts->tv_sec = clock_pair.sec;
-       ts->tv_nsec = clock_pair.nsec;
+       ts->tv_sec = clock_pair->sec;
+       ts->tv_nsec = clock_pair->nsec;
 
        return 0;
 }
@@ -81,9 +118,9 @@ int kvm_arch_ptp_get_crosststamp(u64 *cycle, struct timespec64 *tspec,
                        pr_err_ratelimited("clock pairing hypercall ret %lu\n", ret);
                        return -EOPNOTSUPP;
                }
-               tspec->tv_sec = clock_pair.sec;
-               tspec->tv_nsec = clock_pair.nsec;
-               *cycle = __pvclock_read_cycles(src, clock_pair.tsc);
+               tspec->tv_sec = clock_pair->sec;
+               tspec->tv_nsec = clock_pair->nsec;
+               *cycle = __pvclock_read_cycles(src, clock_pair->tsc);
        } while (pvclock_read_retry(src, version));
 
        *cs = &kvm_clock;

diff --git a/include/linux/ptp_kvm.h b/include/linux/ptp_kvm.h
index c2e28deef33a8d09d4b7014731e2660016ffa8ba..746fd67c34806b0c19959b182a4088f5c560ceb8 100644 (file)
--- a/include/linux/ptp_kvm.h
+++ b/include/linux/ptp_kvm.h
@@ -14,6 +14,7 @@ struct timespec64;
 struct clocksource;
 
 int kvm_arch_ptp_init(void);
+void kvm_arch_ptp_exit(void);
 int kvm_arch_ptp_get_clock(struct timespec64 *ts);
 int kvm_arch_ptp_get_crosststamp(u64 *cycle,
                struct timespec64 *tspec, struct clocksource **cs);