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

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Message-ID: <Z860gFRrwI8Cxycq@kernel.org>
Date: Mon, 10 Mar 2025 11:44:32 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: Vladis Dronov <vdronov@...hat.com>
Cc: linux-sgx@...r.kernel.org, Dave Hansen <dave.hansen@...ux.intel.com>,
	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
Subject: Re: [PATCH] x86/sgx: Warn explicitly if X86_FEATURE_SGX_LC is not
 enabled

On Sun, Mar 09, 2025 at 05:58:06PM +0100, Vladis Dronov wrote:
> 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.
                      ~~~~~~
		      notify

> 
> 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");

I think this should not be error, as the system is not failing.

Since it is informative, it should be info-level message.

>  		return -ENODEV;
> +	}
>  
>  	cpuid_count(SGX_CPUID, 0, &eax, &ebx, &ecx, &edx);
>  
> -- 
> 2.48.1
> 

BR, Jarkko