[RFC PATCH 05/23] x86/cpu/intel: Allow SGX virtualization without Launch Control support

[Kai Huang <kai.huang@xxxxxxxxx>]

From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>

Allow SGX virtualization on systems without Launch Control support, i.e.
allow KVM to expose SGX to guests that support non-LC configurations.

Introduce clear_sgx_lc() to clear SGX_LC feature bit only if SGX Launch
Control is locked by BIOS when SGX virtualization is enabled, to prevent
SGX driver being enabled.

Improve error message to distinguish three cases: 1) SGX disabled
completely by BIOS; 2) SGX disabled completely due to SGX LC is locked
by BIOS, and SGX virtualization is also disabled; 3) Only SGX driver is
disabled due to SGX LC is locked by BIOS, but SGX virtualization is
enabled.

Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Co-developed-by: Kai Huang <kai.huang@xxxxxxxxx>
Signed-off-by: Kai Huang <kai.huang@xxxxxxxxx>
---
 arch/x86/kernel/cpu/feat_ctl.c | 48 +++++++++++++++++++++++++---------
 1 file changed, 36 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kernel/cpu/feat_ctl.c b/arch/x86/kernel/cpu/feat_ctl.c
index 4fcd57fdc682..b07452b68538 100644
--- a/arch/x86/kernel/cpu/feat_ctl.c
+++ b/arch/x86/kernel/cpu/feat_ctl.c
@@ -101,6 +101,11 @@ static void clear_sgx_caps(void)
 	setup_clear_cpu_cap(X86_FEATURE_SGX2);
 }
 
+static void clear_sgx_lc(void)
+{
+	setup_clear_cpu_cap(X86_FEATURE_SGX_LC);
+}
+
 static int __init nosgx(char *str)
 {
 	clear_sgx_caps();
@@ -113,7 +118,7 @@ early_param("nosgx", nosgx);
 void init_ia32_feat_ctl(struct cpuinfo_x86 *c)
 {
 	bool tboot = tboot_enabled();
-	bool enable_sgx;
+	bool enable_sgx_virt, enable_sgx_driver;
 	u64 msr;
 
 	if (rdmsrl_safe(MSR_IA32_FEAT_CTL, &msr)) {
@@ -123,12 +128,19 @@ void init_ia32_feat_ctl(struct cpuinfo_x86 *c)
 	}
 
 	/*
-	 * Enable SGX if and only if the kernel supports SGX and Launch Control
-	 * is supported, i.e. disable SGX if the LE hash MSRs can't be written.
+	 * Enable SGX if and only if the kernel supports SGX.  Require Launch
+	 * Control support if SGX virtualization is *not* supported, i.e.
+	 * disable SGX if the LE hash MSRs can't be written and SGX can't be
+	 * exposed to a KVM guest (which might support non-LC configurations).
 	 */
-	enable_sgx = cpu_has(c, X86_FEATURE_SGX) &&
-		     cpu_has(c, X86_FEATURE_SGX_LC) &&
-		     IS_ENABLED(CONFIG_X86_SGX);
+	enable_sgx_driver = cpu_has(c, X86_FEATURE_SGX) &&
+			    cpu_has(c, X86_FEATURE_SGX1) &&
+			    IS_ENABLED(CONFIG_X86_SGX) &&
+			    cpu_has(c, X86_FEATURE_SGX_LC);
+	enable_sgx_virt = cpu_has(c, X86_FEATURE_SGX) &&
+			  cpu_has(c, X86_FEATURE_SGX1) &&
+			  IS_ENABLED(CONFIG_X86_SGX) &&
+			  IS_ENABLED(CONFIG_X86_SGX_VIRTUALIZATION);
 
 	if (msr & FEAT_CTL_LOCKED)
 		goto update_caps;
@@ -151,8 +163,11 @@ void init_ia32_feat_ctl(struct cpuinfo_x86 *c)
 			msr |= FEAT_CTL_VMX_ENABLED_INSIDE_SMX;
 	}
 
-	if (enable_sgx)
-		msr |= FEAT_CTL_SGX_ENABLED | FEAT_CTL_SGX_LC_ENABLED;
+	if (enable_sgx_driver || enable_sgx_virt) {
+		msr |= FEAT_CTL_SGX_ENABLED;
+		if (enable_sgx_driver)
+			msr |= FEAT_CTL_SGX_LC_ENABLED;
+	}
 
 	wrmsrl(MSR_IA32_FEAT_CTL, msr);
 
@@ -175,10 +190,19 @@ void init_ia32_feat_ctl(struct cpuinfo_x86 *c)
 	}
 
 update_sgx:
-	if (!(msr & FEAT_CTL_SGX_ENABLED) ||
-	    !(msr & FEAT_CTL_SGX_LC_ENABLED) || !enable_sgx) {
-		if (enable_sgx)
-			pr_err_once("SGX disabled by BIOS\n");
+	if (!(msr & FEAT_CTL_SGX_ENABLED)) {
+		if (enable_sgx_driver || enable_sgx_virt)
+			pr_err_once("SGX disabled by BIOS.\n");
 		clear_sgx_caps();
 	}
+	if (!(msr & FEAT_CTL_SGX_LC_ENABLED) &&
+	    (enable_sgx_driver || enable_sgx_virt)) {
+		if (!enable_sgx_virt) {
+			pr_err_once("SGX Launch Control is locked. Disable SGX.\n");
+			clear_sgx_caps();
+		} else if (enable_sgx_driver) {
+			pr_err_once("SGX Launch Control is locked. Disable SGX driver.\n");
+			clear_sgx_lc();
+		}
+	}
 }
-- 
2.29.2