linux-kernel - [PATCH v8 4/5] x86/sgx: Implement ENCLS[EUPDATESVN]

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250715124109.1711717-5-elena.reshetova@intel.com>
Date: Tue, 15 Jul 2025 15:40:21 +0300
From: Elena Reshetova <elena.reshetova@...el.com>
To: dave.hansen@...el.com
Cc: jarkko@...nel.org,
	seanjc@...gle.com,
	kai.huang@...el.com,
	mingo@...nel.org,
	linux-sgx@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	x86@...nel.org,
	asit.k.mallick@...el.com,
	vincent.r.scarlata@...el.com,
	chongc@...gle.com,
	erdemaktas@...gle.com,
	vannapurve@...gle.com,
	bondarn@...gle.com,
	scott.raynor@...el.com,
	Elena Reshetova <elena.reshetova@...el.com>
Subject: [PATCH v8 4/5] x86/sgx: Implement ENCLS[EUPDATESVN]

All running enclaves and cryptographic assets (such as internal SGX
encryption keys) are assumed to be compromised whenever an SGX-related
microcode update occurs. To mitigate this assumed compromise the new
supervisor SGX instruction ENCLS[EUPDATESVN] can generate fresh
cryptographic assets.

Before executing EUPDATESVN, all SGX memory must be marked as unused.
This requirement ensures that no potentially compromised enclave
survives the update and allows the system to safely regenerate
cryptographic assets.

Add the method to perform ENCLS[EUPDATESVN].

Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
---
 arch/x86/kernel/cpu/sgx/encls.h |  5 +++
 arch/x86/kernel/cpu/sgx/main.c  | 61 +++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+)

diff --git a/arch/x86/kernel/cpu/sgx/encls.h b/arch/x86/kernel/cpu/sgx/encls.h
index 99004b02e2ed..d9160c89a93d 100644
--- a/arch/x86/kernel/cpu/sgx/encls.h
+++ b/arch/x86/kernel/cpu/sgx/encls.h
@@ -233,4 +233,9 @@ static inline int __eaug(struct sgx_pageinfo *pginfo, void *addr)
 	return __encls_2(EAUG, pginfo, addr);
 }
 
+/* Attempt to 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 0e75090f93c9..c97bba16e4fd 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -16,6 +16,7 @@
 #include <linux/vmalloc.h>
 #include <asm/msr.h>
 #include <asm/sgx.h>
+#include <asm/archrandom.h>
 #include "driver.h"
 #include "encl.h"
 #include "encls.h"
@@ -920,6 +921,66 @@ EXPORT_SYMBOL_GPL(sgx_set_attribute);
 /* Counter to count the active SGX users */
 static int sgx_usage_count;
 
+/**
+ * sgx_update_svn() - Attempt to call ENCLS[EUPDATESVN].
+ * This instruction attempts to update CPUSVN to the
+ * currently loaded microcode update SVN and generate new
+ * cryptographic assets. Must be called when EPC is empty.
+ * Most of the time, there will be no update and that's OK.
+ * If the failure is due to SGX_INSUFFICIENT_ENTROPY, the
+ * operation can be safely retried. In other failure cases,
+ * the retry should not be attempted.
+ *
+ * Return:
+ * 0: Success or not supported
+ * -EAGAIN: Can be safely retried, failure is due to lack of
+ *  entropy in RNG.
+ * -EIO: Unexpected error, retries are not advisable.
+ */
+static int __maybe_unused sgx_update_svn(void)
+{
+	int ret;
+
+	/*
+	 * If EUPDATESVN is not available, it is ok to
+	 * silently skip it to comply with legacy behavior.
+	 */
+	if (!cpu_feature_enabled(X86_FEATURE_SGX_EUPDATESVN))
+		return 0;
+
+	for (int i = 0; i < RDRAND_RETRY_LOOPS; i++) {
+		ret = __eupdatesvn();
+
+		/* Stop on success or unexpected errors: */
+		if (ret != SGX_INSUFFICIENT_ENTROPY)
+			break;
+	}
+
+	/*
+	 * SVN successfully updated.
+	 * Let users know when the update was successful.
+	 */
+	if (!ret)
+		pr_info("SVN updated successfully\n");
+
+	if (!ret || ret == SGX_NO_UPDATE)
+		return 0;
+
+	/*
+	 * SVN update failed due to lack of entropy in DRNG.
+	 * Indicate to userspace that it should retry.
+	 */
+	if (ret == SGX_INSUFFICIENT_ENTROPY)
+		return -EAGAIN;
+
+	/*
+	 * EUPDATESVN was called when EPC is empty, all other error
+	 * codes are unexpected.
+	 */
+	ENCLS_WARN(ret, "EUPDATESVN");
+	return -EIO;
+}
+
 int sgx_inc_usage_count(void)
 {
 	sgx_usage_count++;
-- 
2.45.2