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From: Kai Huang <kai.huang@intel.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Sean Christopherson <seanjc@google.com>,
	<linux-sgx@vger.kernel.org>, <kvm@vger.kernel.org>,
	<x86@kernel.org>, <jarkko@kernel.org>, <luto@kernel.org>,
	<haitao.huang@intel.com>, <pbonzini@redhat.com>, <bp@alien8.de>,
	<tglx@linutronix.de>, <mingo@redhat.com>, <hpa@zytor.com>
Subject: Re: [RFC PATCH 11/23] x86/sgx: Add helpers to expose ECREATE and EINIT to KVM
Date: Thu, 7 Jan 2021 11:58:39 +1300	[thread overview]
Message-ID: <20210107115839.0767102e8186e9bc89fa0a61@intel.com> (raw)
In-Reply-To: <7df437ee-e1f3-440c-377b-dbe39820fd44@intel.com>

On Wed, 6 Jan 2021 13:23:37 -0800 Dave Hansen wrote:
> On 1/6/21 1:04 PM, Sean Christopherson wrote:
> > On Wed, Jan 06, 2021, Dave Hansen wrote:
> >> On 1/5/21 5:56 PM, Kai Huang wrote:
> >>> From: Sean Christopherson <sean.j.christopherson@intel.com>
> >>>
> >>> Provide wrappers around __ecreate() and __einit() to hide the ugliness
> >>> of overloading the ENCLS return value to encode multiple error formats
> >>> in a single int.  KVM will trap-and-execute ECREATE and EINIT as part
> >>> of SGX virtualization, and on an exception, KVM needs the trapnr so that
> >>> it can inject the correct fault into the guest.
> >>
> >> This is missing a bit of a step about how and why ECREATE needs to be
> >> run in the host in the first place.
> > 
> > There's (hopefully) good info in the KVM usage patch that can be borrowed:
> > 
> >   Add an ECREATE handler that will be used to intercept ECREATE for the
> >   purpose of enforcing and enclave's MISCSELECT, ATTRIBUTES and XFRM, i.e.
> >   to allow userspace to restrict SGX features via CPUID.  ECREATE will be
> >   intercepted when any of the aforementioned masks diverges from hardware
> >   in order to enforce the desired CPUID model, i.e. inject #GP if the
> >   guest attempts to set a bit that hasn't been enumerated as allowed-1 in
> >   CPUID.
> 
> OK, so in plain language: the bare-metal kernel must intercept ECREATE
> to be able to impose policies on guests.  When it does this, the
> bare-metal kernel runs ECREATE against the userspace mapping of the
> virtualized EPC.

Thanks. I'll add this to commit message.

> 
> >>> diff --git a/arch/x86/include/asm/sgx.h b/arch/x86/include/asm/sgx.h
> >>> new file mode 100644
> >>> index 000000000000..0d643b985085
> >>> --- /dev/null
> >>> +++ b/arch/x86/include/asm/sgx.h
> >>> @@ -0,0 +1,16 @@
> >>> +/* SPDX-License-Identifier: GPL-2.0 */
> >>> +#ifndef _ASM_X86_SGX_H
> >>> +#define _ASM_X86_SGX_H
> >>> +
> >>> +#include <linux/types.h>
> >>> +
> >>> +#ifdef CONFIG_X86_SGX_VIRTUALIZATION
> >>> +struct sgx_pageinfo;
> >>> +
> >>> +int sgx_virt_ecreate(struct sgx_pageinfo *pageinfo, void __user *secs,
> >>> +		     int *trapnr);
> >>> +int sgx_virt_einit(void __user *sigstruct, void __user *token,
> >>> +		   void __user *secs, u64 *lepubkeyhash, int *trapnr);
> >>> +#endif
> >>> +
> >>> +#endif /* _ASM_X86_SGX_H */
> >>> diff --git a/arch/x86/kernel/cpu/sgx/virt.c b/arch/x86/kernel/cpu/sgx/virt.c
> >>> index d625551ccf25..4e9810ba9259 100644
> >>> --- a/arch/x86/kernel/cpu/sgx/virt.c
> >>> +++ b/arch/x86/kernel/cpu/sgx/virt.c
> >>> @@ -261,3 +261,58 @@ int __init sgx_virt_epc_init(void)
> >>>  
> >>>  	return misc_register(&sgx_virt_epc_dev);
> >>>  }
> >>> +
> >>> +int sgx_virt_ecreate(struct sgx_pageinfo *pageinfo, void __user *secs,
> >>> +		     int *trapnr)
> >>> +{
> >>> +	int ret;
> >>> +
> >>> +	__uaccess_begin();
> >>> +	ret = __ecreate(pageinfo, (void *)secs);
> >>> +	__uaccess_end();
> >>
> >> The __uaccess_begin/end() worries me.  There are *very* few of these in
> >> the kernel and it seems like something we want to use as sparingly as
> >> possible.
> >>
> >> Why don't we just use the kernel mapping for 'secs' and not have to deal
> >> with stac/clac?
> > 
> > The kernel mapping isn't readily available. 
> 
> Oh, duh.  There's no kernel mapping for EPC... it's not RAM in the first
> place.
> 
> > At this point, it's not even
> > guaranteed that @secs points at an EPC page.  Unlike the driver code, where the
> > EPC page is allocated on-demand by the kernel, the pointer here is userspace
> > (technically guest) controlled.  The caller (KVM) is responsible for ensuring
> > it's a valid userspace address, but the SGX/EPC specific checks are mostly
> > deferred to hardware.
> 
> Ahh, got it.  Kai, could we get some of this into comments or the changelog?

Yes I'll add some into comments.

  reply	other threads:[~2021-01-06 22:59 UTC|newest]

Thread overview: 111+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-06  1:55 [RFC PATCH 00/23] KVM SGX virtualization support Kai Huang
2021-01-06  1:55 ` [RFC PATCH 01/23] x86/sgx: Split out adding EPC page to free list to separate helper Kai Huang
2021-01-11 22:38   ` Jarkko Sakkinen
2021-01-12  0:19     ` Kai Huang
2021-01-12 21:45       ` Sean Christopherson
2021-01-13  1:15         ` Kai Huang
2021-01-13 17:05         ` Jarkko Sakkinen
2021-01-06  1:55 ` [RFC PATCH 02/23] x86/sgx: Add enum for SGX_CHILD_PRESENT error code Kai Huang
2021-01-06 18:28   ` Dave Hansen
2021-01-06 21:40     ` Kai Huang
2021-01-12  0:26     ` Jarkko Sakkinen
2021-01-11 23:32   ` Jarkko Sakkinen
2021-01-12  0:16     ` Kai Huang
2021-01-12  1:46       ` Jarkko Sakkinen
2021-01-06  1:55 ` [RFC PATCH 03/23] x86/sgx: Introduce virtual EPC for use by KVM guests Kai Huang
2021-01-06 19:35   ` Dave Hansen
2021-01-06 20:35     ` Sean Christopherson
2021-01-07  0:47       ` Kai Huang
2021-01-07  0:52         ` Dave Hansen
2021-01-07  1:38           ` Kai Huang
2021-01-07  5:00             ` Dave Hansen
2021-01-07  1:42     ` Kai Huang
2021-01-07  5:02       ` Dave Hansen
2021-01-15 14:07         ` Kai Huang
2021-01-15 15:39           ` Dave Hansen
2021-01-15 21:33             ` Kai Huang
2021-01-15 21:45               ` Sean Christopherson
2021-01-15 22:30                 ` Kai Huang
2021-01-11 23:38   ` Jarkko Sakkinen
2021-01-12  0:56     ` Kai Huang
2021-01-12  1:50       ` Jarkko Sakkinen
2021-01-12  2:03         ` Kai Huang
2021-01-06  1:55 ` [RFC PATCH 04/23] x86/cpufeatures: Add SGX1 and SGX2 sub-features Kai Huang
2021-01-06 19:39   ` Dave Hansen
2021-01-06 22:12     ` Kai Huang
2021-01-06 22:21       ` Dave Hansen
2021-01-06 22:56         ` Kai Huang
2021-01-06 23:19           ` Sean Christopherson
2021-01-06 23:33             ` Dave Hansen
2021-01-06 23:56             ` Kai Huang
2021-01-06 23:40         ` Kai Huang
2021-01-06 23:43           ` Dave Hansen
2021-01-06 23:56             ` Kai Huang
2021-01-06 22:15   ` Borislav Petkov
2021-01-06 23:09     ` Kai Huang
2021-01-07  6:41       ` Borislav Petkov
2021-01-08  2:00         ` Kai Huang
2021-01-08  5:10           ` Dave Hansen
2021-01-08  7:03             ` Kai Huang
2021-01-08  7:17               ` Borislav Petkov
2021-01-08  8:06                 ` Kai Huang
2021-01-08  8:13                   ` Borislav Petkov
2021-01-08  9:00                     ` Kai Huang
2021-01-08 23:55                 ` Sean Christopherson
2021-01-09  0:35                   ` Borislav Petkov
2021-01-09  1:01                     ` Sean Christopherson
2021-01-09  1:19                   ` Borislav Petkov
2021-01-11 17:54                     ` Sean Christopherson
2021-01-11 19:09                       ` Borislav Petkov
2021-01-11 19:20                         ` Sean Christopherson
2021-01-12  2:01                           ` Kai Huang
2021-01-12 12:13                           ` Borislav Petkov
2021-01-12 17:15                             ` Sean Christopherson
2021-01-12 17:51                               ` Borislav Petkov
2021-01-12 21:07                                 ` Kai Huang
2021-01-12 23:17                                   ` Sean Christopherson
2021-01-13  1:05                                     ` Kai Huang
2021-01-11 23:39   ` Jarkko Sakkinen
2021-01-06  1:55 ` [RFC PATCH 05/23] x86/cpu/intel: Allow SGX virtualization without Launch Control support Kai Huang
2021-01-06 19:54   ` Dave Hansen
2021-01-06 22:34     ` Kai Huang
2021-01-06 22:38       ` Dave Hansen
2021-01-06  1:56 ` [RFC PATCH 06/23] x86/sgx: Expose SGX architectural definitions to the kernel Kai Huang
2021-01-06  1:56 ` [RFC PATCH 07/23] x86/sgx: Move ENCLS leaf definitions to sgx_arch.h Kai Huang
2021-01-06  1:56 ` [RFC PATCH 08/23] x86/sgx: Add SGX2 ENCLS leaf definitions (EAUG, EMODPR and EMODT) Kai Huang
2021-01-06  1:56 ` [RFC PATCH 09/23] x86/sgx: Add encls_faulted() helper Kai Huang
2021-01-06  1:56 ` [RFC PATCH 10/23] x86/sgx: Add helper to update SGX_LEPUBKEYHASHn MSRs Kai Huang
2021-01-06 19:56   ` Dave Hansen
2021-01-06  1:56 ` [RFC PATCH 11/23] x86/sgx: Add helpers to expose ECREATE and EINIT to KVM Kai Huang
2021-01-06 20:12   ` Dave Hansen
2021-01-06 21:04     ` Sean Christopherson
2021-01-06 21:23       ` Dave Hansen
2021-01-06 22:58         ` Kai Huang [this message]
2021-01-06  1:56 ` [RFC PATCH 12/23] x86/sgx: Move provisioning device creation out of SGX driver Kai Huang
2021-01-06  1:56 ` [RFC PATCH 13/23] KVM: VMX: Convert vcpu_vmx.exit_reason to a union Kai Huang
2021-01-06  1:56 ` [RFC PATCH 14/23] KVM: x86: Export kvm_mmu_gva_to_gpa_{read,write}() for SGX (VMX) Kai Huang
2021-01-06  1:56 ` [RFC PATCH 15/23] KVM: x86: Define new #PF SGX error code bit Kai Huang
2021-01-06  1:56 ` [RFC PATCH 16/23] KVM: x86: Add SGX feature leaf to reverse CPUID lookup Kai Huang
2021-01-06  1:56 ` [RFC PATCH 17/23] KVM: VMX: Add basic handling of VM-Exit from SGX enclave Kai Huang
2021-01-06  1:56 ` [RFC PATCH 18/23] KVM: VMX: Frame in ENCLS handler for SGX virtualization Kai Huang
2021-01-06  1:56 ` [RFC PATCH 19/23] KVM: VMX: Add SGX ENCLS[ECREATE] handler to enforce CPUID restrictions Kai Huang
2021-01-06  1:56 ` [RFC PATCH 20/23] KVM: VMX: Add emulation of SGX Launch Control LE hash MSRs Kai Huang
2021-01-06  1:56 ` [RFC PATCH 21/23] KVM: VMX: Add ENCLS[EINIT] handler to support SGX Launch Control (LC) Kai Huang
2021-01-06  1:56 ` [RFC PATCH 22/23] KVM: VMX: Enable SGX virtualization for SGX1, SGX2 and LC Kai Huang
2021-01-06  1:58 ` [RFC PATCH 23/23] KVM: x86: Add capability to grant VM access to privileged SGX attribute Kai Huang
2021-01-06  2:22 ` [RFC PATCH 00/23] KVM SGX virtualization support Kai Huang
2021-01-06 17:07 ` Dave Hansen
2021-01-07  0:34   ` Kai Huang
2021-01-07  0:48     ` Dave Hansen
2021-01-07  1:50       ` Kai Huang
2021-01-07 16:14         ` Sean Christopherson
2021-01-08  2:16           ` Kai Huang
2021-01-11 17:20 ` Jarkko Sakkinen
2021-01-11 18:37   ` Sean Christopherson
2021-01-12  1:58     ` Jarkko Sakkinen
2021-01-12  1:14   ` Kai Huang
2021-01-12  2:02     ` Jarkko Sakkinen
2021-01-12  2:07       ` Kai Huang
2021-01-15 14:43         ` Kai Huang
2021-01-16  9:31           ` Jarkko Sakkinen
2021-01-16  9:50             ` Jarkko Sakkinen

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