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From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: "Ayoun, Serge" <serge.ayoun@intel.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"x86@kernel.org" <x86@kernel.org>,
	"linux-sgx@vger.kernel.org" <linux-sgx@vger.kernel.org>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"Hansen, Dave" <dave.hansen@intel.com>,
	"nhorman@redhat.com" <nhorman@redhat.com>,
	"npmccallum@redhat.com" <npmccallum@redhat.com>,
	"Katz-zamir, Shay" <shay.katz-zamir@intel.com>,
	"Huang, Haitao" <haitao.huang@intel.com>,
	"andriy.shevchenko@linux.intel.com" 
	<andriy.shevchenko@linux.intel.com>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"Svahn, Kai" <kai.svahn@intel.com>, "bp@alien8.de" <bp@alien8.de>,
	"josh@joshtriplett.org" <josh@joshtriplett.org>,
	"luto@kernel.org" <luto@kernel.org>,
	"Huang, Kai" <kai.huang@intel.com>,
	"rientjes@google.com" <rientjes@google.com>,
	"Xing, Cedric" <cedric.xing@intel.com>
Subject: Re: [PATCH v21 16/28] x86/sgx: Add the Linux SGX Enclave Driver
Date: Thu, 8 Aug 2019 08:40:00 -0700
Message-ID: <20190808154000.GB23156@linux.intel.com> (raw)
In-Reply-To: <20190807151534.kxsletvhbn3lno6w@linux.intel.com>

On Wed, Aug 07, 2019 at 06:15:34PM +0300, Jarkko Sakkinen wrote:
> On Mon, Jul 29, 2019 at 11:17:57AM +0000, Ayoun, Serge wrote:
> > > +	/* TCS pages need to be RW in the PTEs, but can be 0 in the EPCM. */
> > > +	if ((secinfo.flags & SGX_SECINFO_PAGE_TYPE_MASK) ==
> > > SGX_SECINFO_TCS)
> > > +		prot |= PROT_READ | PROT_WRITE;
> > 
> > For TCS pages you add both RD and WR maximum protection bits.
> > For the enclave to be able to run, user mode will have to change the
> > "vma->vm_flags" from PROT_NONE to PROT_READ | PROT_WRITE (otherwise
> > eenter fails).  This is exactly what your selftest  does.
> 
> Recap where the TCS requirements came from? Why does it need
> RW in PTEs and can be 0 in the EPCM? The comment should explain
> it rather leave it as a claim IMHO.

Hardware ignores SECINFO.FLAGS.{R,W,X} coming from userspace and instead
forces RWX=0.  It does this to prevent software from directly accessing
the TCS.  But hardware still accesses the TCS through a virtual address,
e.g. to allow software to zap the page for reclaim, which means hardware
generates reads and writes to the TCS, i.e. the PTEs need RW permissions.

So, for the EADD ioctl(), it's not unreasonable for userspace to provide
SECINFO.FLAGS.{R,W,X} = 0 for the TCS to match what will actually get
jammed into the EPCM.  Allowing userspace to specify RWX=0 means the
kernel needs to manually add PROT_READ and PROT_WRITE to the allowed prot
bits so that mmap()/mprotect() work as expected.

From the SDM:


(* For TCS pages, force EPCM.rwx bits to 0 and no debug access *)
IF (SCRATCH_SECINFO.FLAGS.PT = PT_TCS)
    THEN
        SCRATCH_SECINFO.FLAGS.R <= 0;
        SCRATCH_SECINFO.FLAGS.W <= 0;
        SCRATCH_SECINFO.FLAGS.X <= 0;
        (DS:RCX).FLAGS.DBGOPTIN <= 0; // force TCS.FLAGS.DBGOPTIN off
        DS:RCX.CSSA <= 0;
        DS:RCX.AEP <= 0;
        DS:RCX.STATE <= 0;
        FI;

  parent reply index

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-13 17:07 [PATCH v21 00/28] Intel SGX foundations Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 01/28] x86/cpufeatures: Add Intel-defined SGX feature bit Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 02/28] x86/cpufeatures: Add SGX sub-features (as Linux-defined bits) Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 03/28] x86/msr: Add IA32_FEATURE_CONTROL.SGX_ENABLE definition Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 04/28] x86/cpufeatures: Add Intel-defined SGX_LC feature bit Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 05/28] x86/msr: Add SGX Launch Control MSR definitions Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 06/28] x86/mm: x86/sgx: Add new 'PF_SGX' page fault error code bit Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 07/28] x86/mm: x86/sgx: Signal SIGSEGV for userspace #PFs w/ PF_SGX Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 08/28] x86/cpu/intel: Detect SGX support and update caps appropriately Jarkko Sakkinen
2019-07-24 19:35   ` Sean Christopherson
2019-08-02 20:48     ` Jarkko Sakkinen
2019-08-07 15:17     ` Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 09/28] x86/sgx: Add ENCLS architectural error codes Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 10/28] x86/sgx: Add SGX1 and SGX2 architectural data structures Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 11/28] x86/sgx: Add wrappers for ENCLS leaf functions Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 12/28] x86/sgx: Enumerate and track EPC sections Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 13/28] x86/sgx: Add functions to allocate and free EPC pages Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 14/28] x86/sgx: Add sgx_einit() for initializing enclaves Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 15/28] mm: Introduce vm_ops->may_mprotect() Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 16/28] x86/sgx: Add the Linux SGX Enclave Driver Jarkko Sakkinen
2019-07-29 11:17   ` Ayoun, Serge
2019-08-07 15:15     ` Jarkko Sakkinen
2019-08-07 15:17       ` Jarkko Sakkinen
2019-08-07 16:45         ` Jethro Beekman
2019-08-08 15:40       ` Sean Christopherson [this message]
2019-08-09 15:02         ` Jarkko Sakkinen
2019-08-09 15:24           ` Sean Christopherson
2019-08-05 16:16   ` Sean Christopherson
2019-08-05 21:39     ` Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 17/28] x86/sgx: Add provisioning Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 18/28] x86/sgx: Add swapping code to the core and SGX driver Jarkko Sakkinen
2019-08-07  6:33   ` Jethro Beekman
2019-08-07 19:12     ` Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 19/28] x86/sgx: ptrace() support for the " Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 20/28] x86/vdso: Add support for exception fixup in vDSO functions Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 21/28] x86/fault: Add helper function to sanitize error code Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 22/28] x86/traps: Attempt to fixup exceptions in vDSO before signaling Jarkko Sakkinen
2019-07-13 17:07 ` [PATCH v21 23/28] x86/vdso: Add __vdso_sgx_enter_enclave() to wrap SGX enclave transitions Jarkko Sakkinen
2019-07-17 22:07   ` Xing, Cedric
2019-07-13 17:08 ` [PATCH v21 24/28] selftests/x86: Add a selftest for SGX Jarkko Sakkinen
2019-07-17 22:37   ` Xing, Cedric
2019-08-02 20:46     ` Jarkko Sakkinen
2019-08-16 15:43     ` Jarkko Sakkinen
2019-08-16 15:51       ` Jarkko Sakkinen
2019-08-16 16:56     ` Jarkko Sakkinen
2019-07-13 17:08 ` [PATCH v21 25/28] x86/sgx: Update MAINTAINERS Jarkko Sakkinen
2019-07-13 17:08 ` [PATCH v21 26/28] docs: x86/sgx: Add Architecture documentation Jarkko Sakkinen
2019-07-13 17:08 ` [PATCH v21 27/28] docs: x86/sgx: Document kernel internals Jarkko Sakkinen
2019-07-13 17:08 ` [PATCH v21 28/28] docs: x86/sgx: Document the enclave API Jarkko Sakkinen
2019-07-14 14:36 ` [PATCH v21 00/28] Intel SGX foundations Jarkko Sakkinen
2019-08-07  6:40   ` Jethro Beekman

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