[RFC PATCH v3 14/27] x86/sgx: Add helpers to expose ECREATE and EINIT to KVM

Kai Huang
2021-01-26T15:29:54Z

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

The bare-metal kernel must intercept ECREATE to be able to impose policies
on guests. When it does this, the bare-metal 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>
---
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 | 93 ++++++++++++++++++++++++++++++++++
2 files changed, 109 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 e1ad7856d878..0f5b0e4e33dd 100644
--- a/arch/x86/kernel/cpu/sgx/virt.c
+++ b/arch/x86/kernel/cpu/sgx/virt.c
@@ -252,3 +252,96 @@ 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_ecreate() - 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, bare-metal driver may rewrite the hardware values, 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