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Subject[PATCH v23 10/24] x86/sgx: Add sgx_einit() for wrapping ENCLS[EINIT]
Date
From: Sean Christopherson <sean.j.christopherson@intel.com>

Enclaves are SGX hosted measured and signed software entities. ENCLS[EINIT]
leaf function checks that the enclave has a legit signed measurement and
transforms the enclave to the state ready for execution. The signed
measurement is provided by the caller in the form of SIGSTRUCT data
structure [1].

Wrap ENCLS[EINIT] into sgx_einit(). Set MSR_IA32_SGXLEPUBKEYHASH* MSRs to
match the public key contained in the SIGSTRUCT [2]. This sets Linux to
enforce a policy where the provided public key is as long as the signed
measurement matches the enclave contents in memory.

Add a per-cpu cache to avoid unnecessary reads and write to the MSRs
as they are expensive operations.

[1] Intel SDM: 37.1.3 ENCLAVE SIGNATURE STRUCTURE (SIGSTRUCT)
[2] Intel SDM: 38.1.4 Intel SGX Launch Control Configuration

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Co-developed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
---
arch/x86/kernel/cpu/sgx/Makefile | 1 +
arch/x86/kernel/cpu/sgx/encls.c | 57 ++++++++++++++++++++++++++++++++
arch/x86/kernel/cpu/sgx/encls.h | 3 ++
3 files changed, 61 insertions(+)
create mode 100644 arch/x86/kernel/cpu/sgx/encls.c

diff --git a/arch/x86/kernel/cpu/sgx/Makefile b/arch/x86/kernel/cpu/sgx/Makefile
index 2dec75916a5e..874492d9e3bd 100644
--- a/arch/x86/kernel/cpu/sgx/Makefile
+++ b/arch/x86/kernel/cpu/sgx/Makefile
@@ -1,3 +1,4 @@
obj-y += \
+ encls.o \
main.o \
reclaim.o
diff --git a/arch/x86/kernel/cpu/sgx/encls.c b/arch/x86/kernel/cpu/sgx/encls.c
new file mode 100644
index 000000000000..44291062967a
--- /dev/null
+++ b/arch/x86/kernel/cpu/sgx/encls.c
@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause)
+// Copyright(c) 2016-19 Intel Corporation.
+
+#include <asm/cpufeature.h>
+#include <asm/traps.h>
+#include "encls.h"
+#include "sgx.h"
+
+/* A per-cpu cache for the last known values of IA32_SGXLEPUBKEYHASHx MSRs. */
+static DEFINE_PER_CPU(u64 [4], sgx_lepubkeyhash_cache);
+
+static void sgx_update_lepubkeyhash_msrs(u64 *lepubkeyhash, bool enforce)
+{
+ u64 *cache;
+ int i;
+
+ cache = per_cpu(sgx_lepubkeyhash_cache, smp_processor_id());
+ for (i = 0; i < 4; i++) {
+ if (enforce || (lepubkeyhash[i] != cache[i])) {
+ wrmsrl(MSR_IA32_SGXLEPUBKEYHASH0 + i, lepubkeyhash[i]);
+ cache[i] = lepubkeyhash[i];
+ }
+ }
+}
+
+/**
+ * sgx_einit - initialize an enclave
+ * @sigstruct: a pointer a SIGSTRUCT
+ * @token: a pointer an EINITTOKEN (optional)
+ * @secs: a pointer a SECS
+ * @lepubkeyhash: the desired value for IA32_SGXLEPUBKEYHASHx MSRs
+ *
+ * Execute ENCLS[EINIT], writing the IA32_SGXLEPUBKEYHASHx MSRs according
+ * to @lepubkeyhash (if possible and necessary).
+ *
+ * Return:
+ * 0 on success,
+ * -errno or SGX error on failure
+ */
+int sgx_einit(struct sgx_sigstruct *sigstruct, struct sgx_einittoken *token,
+ struct sgx_epc_page *secs, u64 *lepubkeyhash)
+{
+ int ret;
+
+ if (!boot_cpu_has(X86_FEATURE_SGX_LC))
+ return __einit(sigstruct, token, sgx_epc_addr(secs));
+
+ preempt_disable();
+ sgx_update_lepubkeyhash_msrs(lepubkeyhash, false);
+ ret = __einit(sigstruct, token, sgx_epc_addr(secs));
+ if (ret == SGX_INVALID_EINITTOKEN) {
+ sgx_update_lepubkeyhash_msrs(lepubkeyhash, true);
+ ret = __einit(sigstruct, token, sgx_epc_addr(secs));
+ }
+ preempt_enable();
+ return ret;
+}
diff --git a/arch/x86/kernel/cpu/sgx/encls.h b/arch/x86/kernel/cpu/sgx/encls.h
index d6381e4f6eb2..af94bbfe4cf6 100644
--- a/arch/x86/kernel/cpu/sgx/encls.h
+++ b/arch/x86/kernel/cpu/sgx/encls.h
@@ -248,4 +248,7 @@ static inline int __ewb(struct sgx_pageinfo *pginfo, void *addr,
return __encls_ret_3(EWB, pginfo, addr, va);
}

+int sgx_einit(struct sgx_sigstruct *sigstruct, struct sgx_einittoken *token,
+ struct sgx_epc_page *secs, u64 *lepubkeyhash);
+
#endif /* _X86_ENCLS_H */
--
2.20.1
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