[RFC PATCH v4 13/26] x86/sgx: Add helpers to expose ECREATE and EINIT to KVM

Kai Huang
2021-02-08T11:05:50Z

From: Sean Christopherson <sean.j.christopherson@intel.com>

The host kernel must intercept ECREATE to be able to impose policies on
guests. When it does this, the host kernel runs ECREATE against the
userspace mapping of the virtualized EPC.

Provide wrappers around __ecreate() and __einit() to hide the ugliness
of overloading the ENCLS return value to encode multiple error formats
in a single int. KVM will trap-and-execute ECREATE and EINIT as part
of SGX virtualization, and on an exception, KVM needs the trapnr so that
it can inject the correct fault into the guest.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Kai Huang <kai.huang@intel.com>
---
v3->v4:

- Added one new line before last return in sgx_virt_einit(), per Jarkko.

v2->v3:

- Added kdoc for sgx_virt_ecreate() and sgx_virt_einit(), per Jarkko.
- Changed to use CONFIG_X86_SGX_KVM.

---
arch/x86/include/asm/sgx.h | 16 ++++++
arch/x86/kernel/cpu/sgx/virt.c | 94 ++++++++++++++++++++++++++++++++++
2 files changed, 110 insertions(+)
create mode 100644 arch/x86/include/asm/sgx.h

diff --git a/arch/x86/include/asm/sgx.h b/arch/x86/include/asm/sgx.h
new file mode 100644
index 000000000000..8a3ea3e1efbe
--- /dev/null
+++ b/arch/x86/include/asm/sgx.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_SGX_H
+#define _ASM_X86_SGX_H
+
+#include <linux/types.h>
+
+#ifdef CONFIG_X86_SGX_KVM
+struct sgx_pageinfo;
+
+int sgx_virt_ecreate(struct sgx_pageinfo *pageinfo, void __user *secs,
+ int *trapnr);
+int sgx_virt_einit(void __user *sigstruct, void __user *token,
+ void __user *secs, u64 *lepubkeyhash, int *trapnr);
+#endif
+
+#endif /* _ASM_X86_SGX_H */
diff --git a/arch/x86/kernel/cpu/sgx/virt.c b/arch/x86/kernel/cpu/sgx/virt.c
index 47542140f8c1..016bad7cff8d 100644
--- a/arch/x86/kernel/cpu/sgx/virt.c
+++ b/arch/x86/kernel/cpu/sgx/virt.c
@@ -257,3 +257,97 @@ int __init sgx_vepc_init(void)

return misc_register(&sgx_vepc_dev);
}
+
+/**
+ * sgx_virt_ecreate() - Run ECREATE on behalf of guest
+ * @pageinfo: Pointer to PAGEINFO structure
+ * @secs: Userspace pointer to SECS page
+ * @trapnr: trap number injected to guest in case of ECREATE error
+ *
+ * Run ECREATE on behalf of guest after KVM traps ECREATE for the purpose
+ * of enforcing policies of guest's enclaves, and return the trap number
+ * which should be injected to guest in case of any ECREATE error.
+ *
+ * Return:
+ * - 0: ECREATE was successful.
+ * - -EFAULT: ECREATE returned error.
+ */
+int sgx_virt_ecreate(struct sgx_pageinfo *pageinfo, void __user *secs,
+ int *trapnr)
+{
+ int ret;
+
+ /*
+ * @secs is userspace address, and it's not guaranteed @secs points at
+ * an actual EPC page. It's also possible to generate a kernel mapping
+ * to physical EPC page by resolving PFN but using __uaccess_xx() is
+ * simpler.
+ */
+ __uaccess_begin();
+ ret = __ecreate(pageinfo, (void *)secs);
+ __uaccess_end();
+
+ if (encls_faulted(ret)) {
+ *trapnr = ENCLS_TRAPNR(ret);
+ return -EFAULT;
+ }
+
+ /* ECREATE doesn't return an error code, it faults or succeeds. */
+ WARN_ON_ONCE(ret);
+ return 0;
+}
+EXPORT_SYMBOL_GPL(sgx_virt_ecreate);
+
+static int __sgx_virt_einit(void __user *sigstruct, void __user *token,
+ void __user *secs)
+{
+ int ret;
+
+ __uaccess_begin();
+ ret = __einit((void *)sigstruct, (void *)token, (void *)secs);
+ __uaccess_end();
+ return ret;
+}
+
+/**
+ * sgx_virt_einit() - Run EINIT on behalf of guest
+ * @sigstruct: Userspace pointer to SIGSTRUCT structure
+ * @token: Userspace pointer to EINITTOKEN structure
+ * @secs: Userspace pointer to SECS page
+ * @lepubkeyhash: Pointer to guest's *virtual* SGX_LEPUBKEYHASH MSR
+ * values
+ * @trapnr: trap number injected to guest in case of EINIT error
+ *
+ * Run EINIT on behalf of guest after KVM traps EINIT. If SGX_LC is available
+ * in host, SGX driver may rewrite the hardware values at wish, therefore KVM
+ * needs to update hardware values to guest's virtual MSR values in order to
+ * ensure EINIT is executed with expected hardware values.
+ *
+ * Return:
+ * - 0: EINIT was successful.
+ * - -EFAULT: EINIT returned error.
+ */
+int sgx_virt_einit(void __user *sigstruct, void __user *token,
+ void __user *secs, u64 *lepubkeyhash, int *trapnr)
+{
+ int ret;
+
+ if (!boot_cpu_has(X86_FEATURE_SGX_LC)) {
+ ret = __sgx_virt_einit(sigstruct, token, secs);
+ } else {
+ preempt_disable();
+
+ sgx_update_lepubkeyhash(lepubkeyhash);
+
+ ret = __sgx_virt_einit(sigstruct, token, secs);
+ preempt_enable();
+ }
+
+ if (encls_faulted(ret)) {
+ *trapnr = ENCLS_TRAPNR(ret);
+ return -EFAULT;
+ }
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(sgx_virt_einit);
--
2.29.2