linux-kernel - [PATCH] x86/sgx: Warn explicitly if X86_FEATURE_SGX

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Message-ID: <20250309165805.8996-2-vdronov@redhat.com>
Date: Sun,  9 Mar 2025 17:58:06 +0100
From: Vladis Dronov <vdronov@...hat.com>
To: linux-sgx@...r.kernel.org,
	Jarkko Sakkinen <jarkko@...nel.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org,
	Vladis Dronov <vdronov@...hat.com>
Subject: [PATCH] x86/sgx: Warn explicitly if X86_FEATURE_SGX_LC is not enabled

A kernel requires X86_FEATURE_SGX_LC to be able to create SGX enclaves.
There is quite a number of hardware which has X86_FEATURE_SGX but not
X86_FEATURE_SGX_LC. A kernel running on such a hardware does not create
/dev/sgx* devices silently. Explicitly warn if X86_FEATURE_SGX_LC is not
enabled to properly nofity a user about this condition.

The X86_FEATURE_SGX_LC is a CPU feature that enables LE hash MSRs to be
writable when running native enclaves, i.e. using a custom root key rather
than the Intel proprietary key for enclave signing.

Signed-off-by: Vladis Dronov <vdronov@...hat.com>
---

an out-of-commit-message note:

I've hit this issue myself and have spent some time researching where are
my /dev/sgx* devices on an SGX-enabled hardware, so this is a bit personal.

Links related:
https://github.com/intel/linux-sgx/issues/837
https://patchwork.kernel.org/project/platform-driver-x86/patch/20180827185507.17087-3-jarkko.sakkinen@linux.intel.com/

 arch/x86/kernel/cpu/sgx/driver.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/sgx/driver.c b/arch/x86/kernel/cpu/sgx/driver.c
index 22b65a5f5ec6..df4fbfaa6616 100644
--- a/arch/x86/kernel/cpu/sgx/driver.c
+++ b/arch/x86/kernel/cpu/sgx/driver.c
@@ -150,8 +150,10 @@ int __init sgx_drv_init(void)
 	u64 xfrm_mask;
 	int ret;

-	if (!cpu_feature_enabled(X86_FEATURE_SGX_LC))
+	if (!cpu_feature_enabled(X86_FEATURE_SGX_LC)) {
+		pr_err("SGX disabled: SGX launch control is not available.\n");
 		return -ENODEV;
+	}

 	cpuid_count(SGX_CPUID, 0, &eax, &ebx, &ecx, &edx);

-- 
2.48.1