* Huang, Kai <kai.hu...@intel.com> wrote:
> On Sun, 2025-03-09 at 18:22 +0100, Vladis Dronov wrote: > > A kernel requires X86_FEATURE_SGX_LC to be able to create SGX enclaves. > > The kernel requires ... > > > 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_enclave file silently. Explicitly warn if X86_FEATURE_SGX_LC > > is not enabled to properly nofity a user about this condition. > ^ > notify > > And I don't think "notify" is correct because the reality is the > kernel only prints some error message so that the user can check and > see when it wants. > > How about: > > Explicitly print error message if X86_FEATURE_SGX_LC is not present > so that the users can be aware of this condition which results in SGX > driver being disabled. > > > > > 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. > > Using "root key" can be controversial. Let's just say "key" instead. > > And the X86_FEATURE_SGX_LC feature itself doesn't automatically enable LE MSRs > to be writable. We still need to opt-in in the 'feature control' MSR. Why would it be controversial? > How about: > > The X86_FEATURE_SGX_LC, a.k.a. SGX Launch Control, is a CPU feature > that enables LE (Launch Enclave) hash MSRs to be writable (with > additional opt-in required in the 'feature control' MSR) when running > enclaves, i.e., using a custom key rather than the Intel proprietary > key for enclave signing. > > Signed-off-by: Vladis Dronov <vdro...@redhat.com> > > I think this message will be useful for someone who knows SGX in > general but doesn't know that Linux SGX driver requires the LE MSRs > to be writable, thus requires the CPU supports SGX_LC feature bit. > > With the above addressed, feel free to add: > > Acked-by: Kai Huang <kai.hu...@intel.com> Thanks, I've edited the changelog to be a bit clearer. I also added an error message when the driver fails to register, and made all 3 failure error messages consistent and refer back to the /dev/sgx_enclave device node name. I also included part of this commit message note: > > an out-of-commit-message note: > > > > I've hit this issue myself and have spent some time researching where is > > my /dev/sgx_enclave file 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.sakki...@linux.intel.com/ Because this experience reflects arguably poor usability: people see 'SGX' in their /proc/cpuinfo file, think that their hardware is 'SGX enabled' and are wondering why the hell the /dev/sgx_enclave device node is not created, right? I also Cc:-ed more SGX people. See the full -v3 patch below. Is the device node misnamed, should it be /dev/sgx_lc_enclave? Should we hide the SGX feature bit from cpuinfo when SGX_LC is not present, so that people don't go on a wild goose chase? Thanks, Ingo ======================================> From: Vladis Dronov <vdro...@redhat.com> Date: Sun, 9 Mar 2025 18:22:16 +0100 Subject: [PATCH] x86/sgx: Warn explicitly if X86_FEATURE_SGX_LC is not enabled The kernel requires X86_FEATURE_SGX_LC to be able to create SGX enclaves, not just X86_FEATURE_SGX. There is quite a number of hardware which has X86_FEATURE_SGX but not X86_FEATURE_SGX_LC. A kernel running on such hardware does not create the /dev/sgx_enclave file and does so silently. Explicitly warn if X86_FEATURE_SGX_LC is not enabled to properly notify users that the kernel disabled the SGX driver. The X86_FEATURE_SGX_LC, a.k.a. SGX Launch Control, is a CPU feature that enables LE (Launch Enclave) hash MSRs to be writable (with additional opt-in required in the 'feature control' MSR) when running enclaves, i.e. using a custom root key rather than the Intel proprietary key for enclave signing. I've hit this issue myself and have spent some time researching where my /dev/sgx_enclave file went on SGX-enabled hardware. Related links: https://github.com/intel/linux-sgx/issues/837 https://patchwork.kernel.org/project/platform-driver-x86/patch/20180827185507.17087-3-jarkko.sakki...@linux.intel.com/ [ mingo: Made the error message a bit more verbose, and added other cases where the kernel fails to create the /dev/sgx_enclave device node. ] Signed-off-by: Vladis Dronov <vdro...@redhat.com> Signed-off-by: Ingo Molnar <mi...@kernel.org> Acked-by: Kai Huang <kai.hu...@intel.com> Cc: Jarkko Sakkinen <jar...@kernel.org> Cc: Andy Lutomirski <l...@kernel.org> Cc: Sean Christopherson <sean.j.christopher...@intel.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Peter Zijlstra <pet...@infradead.org> Link: https://lore.kernel.org/r/20250309172215.21777-2-vdro...@redhat.com --- arch/x86/kernel/cpu/sgx/driver.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/cpu/sgx/driver.c b/arch/x86/kernel/cpu/sgx/driver.c index 22b65a5f5ec6..40c3347ac65d 100644 --- a/arch/x86/kernel/cpu/sgx/driver.c +++ b/arch/x86/kernel/cpu/sgx/driver.c @@ -150,13 +150,15 @@ 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 CPU feature is not available, /dev/sgx_enclave disabled.\n"); return -ENODEV; + } cpuid_count(SGX_CPUID, 0, &eax, &ebx, &ecx, &edx); if (!(eax & 1)) { - pr_err("SGX disabled: SGX1 instruction support not available.\n"); + pr_err("SGX disabled: SGX1 instruction support not available, /dev/sgx_enclave disabled.\n"); return -ENODEV; } @@ -173,8 +175,10 @@ int __init sgx_drv_init(void) } ret = misc_register(&sgx_dev_enclave); - if (ret) + if (ret) { + pr_err("SGX disabled: Unable to register the /dev/sgx_enclave driver (%d).\n", ret); return ret; + } return 0; }
