[PATCH v4 7/9] x86/sgx: Implement ENCLS[EUPDATESVN]

Cathy Zhang
2022-04-21T11:05:47Z

The SGX attestation architecture assumes a compromise of all running
enclaves and cryptographic assets (like internal SGX encryption keys)
whenever a microcode update affects SGX. To mitigate the impact of
this presumed compromise, a new supervisor SGX instruction:
ENCLS[EUPDATESVN], is introduced to update SGX microcode version and
generate new cryptographic assets in runtime after SGX microcode
update.

EUPDATESVN requires that SGX memory to be marked as "unused" before
it will succeed. This ensures that no compromised enclave can survive
the process and provides an opportunity to generate new cryptographic
assets.

Signed-off-by: Cathy Zhang <cathy.zhang@intel.com>

---
Changes since v1:
- Print message for each return code to notify userspace the
ENCLS[EUPDATESVN] execution status.
---
arch/x86/include/asm/sgx.h | 33 +++++++++++----------
arch/x86/kernel/cpu/sgx/encls.h | 6 ++++
arch/x86/kernel/cpu/sgx/main.c | 52 +++++++++++++++++++++++++++++++++
3 files changed, 76 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/sgx.h b/arch/x86/include/asm/sgx.h
index 4a8ca7281229..74bcb6841a4b 100644
--- a/arch/x86/include/asm/sgx.h
+++ b/arch/x86/include/asm/sgx.h
@@ -26,23 +26,26 @@
#define SGX_CPUID_EPC_SECTION 0x1
/* The bitmask for the EPC section type. */
#define SGX_CPUID_EPC_MASK GENMASK(3, 0)
+/* EUPDATESVN presence indication */
+#define SGX_CPUID_EUPDATESVN BIT(10)

enum sgx_encls_function {
- ECREATE = 0x00,
- EADD = 0x01,
- EINIT = 0x02,
- EREMOVE = 0x03,
- EDGBRD = 0x04,
- EDGBWR = 0x05,
- EEXTEND = 0x06,
- ELDU = 0x08,
- EBLOCK = 0x09,
- EPA = 0x0A,
- EWB = 0x0B,
- ETRACK = 0x0C,
- EAUG = 0x0D,
- EMODPR = 0x0E,
- EMODT = 0x0F,
+ ECREATE = 0x00,
+ EADD = 0x01,
+ EINIT = 0x02,
+ EREMOVE = 0x03,
+ EDGBRD = 0x04,
+ EDGBWR = 0x05,
+ EEXTEND = 0x06,
+ ELDU = 0x08,
+ EBLOCK = 0x09,
+ EPA = 0x0A,
+ EWB = 0x0B,
+ ETRACK = 0x0C,
+ EAUG = 0x0D,
+ EMODPR = 0x0E,
+ EMODT = 0x0F,
+ EUPDATESVN = 0x18,
};

/**
diff --git a/arch/x86/kernel/cpu/sgx/encls.h b/arch/x86/kernel/cpu/sgx/encls.h
index 60321c5f5718..8455f385e817 100644
--- a/arch/x86/kernel/cpu/sgx/encls.h
+++ b/arch/x86/kernel/cpu/sgx/encls.h
@@ -208,4 +208,10 @@ static inline int __ewb(struct sgx_pageinfo *pginfo, void *addr,
return __encls_ret_3(EWB, pginfo, addr, va);
}

+/* Update CPUSVN at runtime. */
+static inline int __eupdatesvn(void)
+{
+ return __encls_ret_1(EUPDATESVN, "");
+}
+
#endif /* _X86_ENCLS_H */
diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 72317866ddaa..fbb093c9fe1a 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -1357,3 +1357,55 @@ void sgx_zap_abort(void)
sgx_zap_abort_wait = true;
wake_up(&sgx_zap_waitq);
}
+
+/**
+ * sgx_updatesvn() - Issue ENCLS[EUPDATESVN]
+ * If EPC is ready, this instruction will update CPUSVN to the currently
+ * loaded microcode update SVN and generate new cryptographic assets.
+ *
+ * Return:
+ * 0: CPUSVN is update successfully.
+ * %SGX_LOCKFAIL: An instruction concurrency rule was violated.
+ * %SGX_INSUFFICIENT_ENTROPY: Insufficient entropy in RNG.
+ * %SGX_EPC_NOT_READY: EPC is not ready for SVN update.
+ * %SGX_NO_UPDATE: EUPDATESVN was successful, but CPUSVN was not
+ * updated because current SVN was not newer than
+ * CPUSVN.
+ */
+static int sgx_updatesvn(void)
+{
+ int ret;
+ int retry = 10;
+
+ do {
+ ret = __eupdatesvn();
+ if (ret != SGX_INSUFFICIENT_ENTROPY)
+ break;
+
+ } while (--retry);
+
+ switch (ret) {
+ case 0:
+ pr_info("EUPDATESVN was successful!\n");
+ break;
+ case SGX_NO_UPDATE:
+ pr_info("EUPDATESVN was successful, but CPUSVN was not updated, "
+ "because current SVN was not newer than CPUSVN.\n");
+ break;
+ case SGX_EPC_NOT_READY:
+ pr_info("EPC is not ready for SVN update.");
+ break;
+ case SGX_INSUFFICIENT_ENTROPY:
+ pr_info("CPUSVN update is failed due to Insufficient entropy in RNG, "
+ "please try it later.\n");
+ break;
+ case SGX_EPC_PAGE_CONFLICT:
+ pr_info("CPUSVN update is failed due to concurrency violation, please "
+ "stop running any other ENCLS leaf and try it later.\n");
+ break;
+ default:
+ break;
+ }
+
+ return ret;
+}
--
2.17.1