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From: "Xing, Cedric" <cedric.xing@intel.com>
To: "Christopherson, Sean J" <sean.j.christopherson@intel.com>,
	"Jarkko Sakkinen" <jarkko.sakkinen@linux.intel.com>
Cc: "linux-sgx@vger.kernel.org" <linux-sgx@vger.kernel.org>,
	"linux-security-module@vger.kernel.org" 
	<linux-security-module@vger.kernel.org>,
	"selinux@vger.kernel.org" <selinux@vger.kernel.org>,
	"Roberts, William C" <william.c.roberts@intel.com>,
	"Schaufler, Casey" <casey.schaufler@intel.com>,
	James Morris <jmorris@namei.org>,
	"Hansen, Dave" <dave.hansen@intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Jethro Beekman <jethro@fortanix.com>,
	"Dr . Greg Wettstein" <greg@enjellic.com>,
	"Stephen Smalley" <sds@tycho.nsa.gov>
Subject: RE: [RFC PATCH v4 04/12] x86/sgx: Require userspace to define enclave pages' protection bits
Date: Fri, 21 Jun 2019 16:42:54 +0000
Message-ID: <960B34DE67B9E140824F1DCDEC400C0F65518451@ORSMSX116.amr.corp.intel.com> (raw)
In-Reply-To: <20190619222401.14942-5-sean.j.christopherson@intel.com>

> From: Christopherson, Sean J
> Sent: Wednesday, June 19, 2019 3:24 PM
> 
> diff --git a/arch/x86/include/uapi/asm/sgx.h b/arch/x86/include/uapi/asm/sgx.h index
> 6dba9f282232..67a3babbb24d 100644
> --- a/arch/x86/include/uapi/asm/sgx.h
> +++ b/arch/x86/include/uapi/asm/sgx.h
> @@ -35,15 +35,17 @@ struct sgx_enclave_create  {
>   * @src:	address for the page data
>   * @secinfo:	address for the SECINFO data
>   * @mrmask:	bitmask for the measured 256 byte chunks
> + * @prot:	maximal PROT_{READ,WRITE,EXEC} protections for the page
>   */
>  struct sgx_enclave_add_page {
>  	__u64	addr;
>  	__u64	src;
>  	__u64	secinfo;
> -	__u64	mrmask;
> +	__u16	mrmask;
> +	__u8	prot;
> +	__u8	pad;
>  };

Given EPCM permissions cannot change in SGX1, these maximal PROT_* flags can be the same as EPCM permissions, so don't have to be specified by user code until SGX2. Given we don't have a clear picture on how SGX2 will work yet, I think we shall take "prot" off until it is proven necessary. 

> diff --git a/arch/x86/kernel/cpu/sgx/driver/main.c b/arch/x86/kernel/cpu/sgx/driver/main.c
> index 29384cdd0842..dabfe2a7245a 100644
> --- a/arch/x86/kernel/cpu/sgx/driver/main.c
> +++ b/arch/x86/kernel/cpu/sgx/driver/main.c
> @@ -93,15 +93,64 @@ static long sgx_compat_ioctl(struct file *filep, unsigned int cmd,  }
> #endif
> 
> +/*
> + * Returns the AND of VM_{READ,WRITE,EXEC} permissions across all pages
> + * covered by the specific VMA.  A non-existent (or yet to be added)
> +enclave
> + * page is considered to have no RWX permissions, i.e. is inaccessible.
> + */
> +static unsigned long sgx_allowed_rwx(struct sgx_encl *encl,
> +				     struct vm_area_struct *vma)
> +{
> +	unsigned long allowed_rwx = VM_READ | VM_WRITE | VM_EXEC;
> +	unsigned long idx, idx_start, idx_end;
> +	struct sgx_encl_page *page;
> +
> +	idx_start = PFN_DOWN(vma->vm_start);
> +	idx_end = PFN_DOWN(vma->vm_end - 1);
> +
> +	for (idx = idx_start; idx <= idx_end; ++idx) {
> +		/*
> +		 * No need to take encl->lock, vm_prot_bits is set prior to
> +		 * insertion and never changes, and racing with adding pages is
> +		 * a userspace bug.
> +		 */
> +		rcu_read_lock();
> +		page = radix_tree_lookup(&encl->page_tree, idx);
> +		rcu_read_unlock();

This loop iterates through every page in the range, which could be very slow if the range is large.

> +
> +		/* Do not allow R|W|X to a non-existent page. */
> +		if (!page)
> +			allowed_rwx = 0;
> +		else
> +			allowed_rwx &= page->vm_prot_bits;
> +		if (!allowed_rwx)
> +			break;
> +	}
> +
> +	return allowed_rwx;
> +}
> +
>  static int sgx_mmap(struct file *file, struct vm_area_struct *vma)  {
>  	struct sgx_encl *encl = file->private_data;
> +	unsigned long allowed_rwx;
>  	int ret;
> 
> +	allowed_rwx = sgx_allowed_rwx(encl, vma);
> +	if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC) & ~allowed_rwx)
> +		return -EACCES;
> +
>  	ret = sgx_encl_mm_add(encl, vma->vm_mm);
>  	if (ret)
>  		return ret;
> 
> +	if (!(allowed_rwx & VM_READ))
> +		vma->vm_flags &= ~VM_MAYREAD;
> +	if (!(allowed_rwx & VM_WRITE))
> +		vma->vm_flags &= ~VM_MAYWRITE;
> +	if (!(allowed_rwx & VM_EXEC))
> +		vma->vm_flags &= ~VM_MAYEXEC;
> +

Say a range comprised of a RW sub-range and a RX sub-range is being mmap()'ed as R here. It'd succeed but mprotect(<RW sub-range>, RW) afterwards will fail because VM_MAYWRITE is cleared here. However, if those two sub-ranges are mapped by separate mmap() calls then the same mprotect() would succeed. The inconsistence here is unexpected and unprecedented.

>  	vma->vm_ops = &sgx_vm_ops;
>  	vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP | VM_IO;
>  	vma->vm_private_data = encl;


  parent reply index

Thread overview: 156+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-19 22:23 [RFC PATCH v4 00/12] security: x86/sgx: SGX vs. LSM Sean Christopherson
2019-06-19 22:23 ` [RFC PATCH v4 01/12] x86/sgx: Use mmu_notifier.release() instead of per-vma refcounting Sean Christopherson
2019-06-20 21:03   ` Jarkko Sakkinen
2019-07-08 14:57     ` Sean Christopherson
2019-07-09 16:18       ` Jarkko Sakkinen
2019-06-19 22:23 ` [RFC PATCH v4 02/12] x86/sgx: Do not naturally align MAP_FIXED address Sean Christopherson
2019-06-20 21:09   ` Jarkko Sakkinen
2019-06-20 22:09     ` Jarkko Sakkinen
2019-06-19 22:23 ` [RFC PATCH v4 03/12] selftests: x86/sgx: Mark the enclave loader as not needing an exec stack Sean Christopherson
2019-06-20 21:17   ` Jarkko Sakkinen
2019-06-19 22:23 ` [RFC PATCH v4 04/12] x86/sgx: Require userspace to define enclave pages' protection bits Sean Christopherson
2019-06-21  1:07   ` Jarkko Sakkinen
2019-06-21  1:16     ` Jarkko Sakkinen
2019-06-21 16:42   ` Xing, Cedric [this message]
2019-07-08 16:34     ` Sean Christopherson
2019-07-08 17:29       ` Xing, Cedric
2019-07-01 18:00   ` Andy Lutomirski
2019-07-01 19:22     ` Xing, Cedric
2019-06-19 22:23 ` [RFC PATCH v4 05/12] x86/sgx: Enforce noexec filesystem restriction for enclaves Sean Christopherson
2019-06-21  1:26   ` Jarkko Sakkinen
2019-07-07 19:03     ` Sean Christopherson
2019-06-19 22:23 ` [RFC PATCH v4 06/12] mm: Introduce vm_ops->may_mprotect() Sean Christopherson
2019-06-21  1:35   ` Jarkko Sakkinen
2019-06-19 22:23 ` [RFC PATCH v4 07/12] LSM: x86/sgx: Introduce ->enclave_map() hook for Intel SGX Sean Christopherson
2019-06-21  2:28   ` Jarkko Sakkinen
2019-06-21 16:54   ` Xing, Cedric
2019-06-25 20:48     ` Stephen Smalley
2019-06-27 20:29       ` Xing, Cedric
2019-07-07 18:01         ` Sean Christopherson
2019-06-19 22:23 ` [RFC PATCH v4 08/12] security/selinux: Require SGX_MAPWX to map enclave page WX Sean Christopherson
2019-06-21 17:09   ` Xing, Cedric
2019-06-25 21:05     ` Stephen Smalley
2019-06-27 20:26       ` Xing, Cedric
2019-06-25 20:19   ` Stephen Smalley
2019-06-26 12:49     ` Dr. Greg
2019-06-19 22:23 ` [RFC PATCH v4 09/12] LSM: x86/sgx: Introduce ->enclave_load() hook for Intel SGX Sean Christopherson
2019-06-21 17:05   ` Xing, Cedric
2019-06-25 21:01     ` Stephen Smalley
2019-06-25 21:49       ` Stephen Smalley
2019-06-27 19:38         ` Xing, Cedric
2019-06-19 22:23 ` [RFC PATCH v4 10/12] security/selinux: Add enclave_load() implementation Sean Christopherson
2019-06-21 21:22   ` Xing, Cedric
2019-06-25 21:09     ` Stephen Smalley
2019-06-27 20:19       ` Xing, Cedric
2019-06-28 16:16         ` Stephen Smalley
2019-06-28 21:20           ` Xing, Cedric
2019-06-29  1:15             ` Stephen Smalley
2019-07-01 18:14               ` Xing, Cedric
2019-06-29 23:41       ` Andy Lutomirski
2019-07-01 17:46         ` Xing, Cedric
2019-07-01 17:53           ` Andy Lutomirski
2019-07-01 18:54             ` Xing, Cedric
2019-07-01 19:03               ` Xing, Cedric
2019-07-01 19:32               ` Andy Lutomirski
2019-07-01 20:03                 ` Xing, Cedric
2019-07-07 18:46                   ` Sean Christopherson
2019-06-25 20:34   ` Stephen Smalley
2019-06-19 22:24 ` [RFC PATCH v4 11/12] security/apparmor: " Sean Christopherson
2019-06-19 22:24 ` [RFC PATCH v4 12/12] LSM: x86/sgx: Show line of sight to LSM support SGX2's EAUG Sean Christopherson
2019-06-21 17:18   ` Xing, Cedric
2019-07-08 14:34     ` Sean Christopherson
2019-06-21  1:32 ` [RFC PATCH v4 00/12] security: x86/sgx: SGX vs. LSM Jarkko Sakkinen
2019-06-27 18:56 ` [RFC PATCH v2 0/3] security/x86/sgx: SGX specific LSM hooks Cedric Xing
2019-07-03 23:16   ` Jarkko Sakkinen
2019-07-03 23:22     ` Jarkko Sakkinen
2019-07-03 23:23       ` Jarkko Sakkinen
2019-07-06  5:04     ` Xing, Cedric
2019-07-08 14:46       ` Jarkko Sakkinen
2019-07-07 23:41   ` [RFC PATCH v3 0/4] " Cedric Xing
2019-07-08 15:55     ` Sean Christopherson
2019-07-08 17:49       ` Xing, Cedric
2019-07-08 18:49         ` Sean Christopherson
2019-07-08 22:26           ` Xing, Cedric
2019-07-07 23:41   ` [RFC PATCH v3 1/4] x86/sgx: Add " Cedric Xing
2019-07-07 23:41   ` [RFC PATCH v3 2/4] x86/64: Call LSM hooks from SGX subsystem/module Cedric Xing
2019-07-09  1:03     ` Sean Christopherson
2019-07-07 23:41   ` [RFC PATCH v3 3/4] X86/sgx: Introduce EMA as a new LSM module Cedric Xing
2019-07-08 16:26     ` Casey Schaufler
2019-07-08 17:16       ` Xing, Cedric
2019-07-08 23:53         ` Casey Schaufler
2019-07-09 22:13           ` Xing, Cedric
2019-07-10  0:10             ` Casey Schaufler
2019-07-10  0:55               ` Xing, Cedric
2019-07-10 21:14                 ` Casey Schaufler
2019-07-11 13:51                 ` Stephen Smalley
2019-07-11 15:12                   ` Sean Christopherson
2019-07-11 16:11                     ` Stephen Smalley
2019-07-11 16:25                       ` Sean Christopherson
2019-07-11 16:32                         ` Stephen Smalley
2019-07-11 23:41                           ` Xing, Cedric
2019-07-07 23:41   ` [RFC PATCH v3 4/4] x86/sgx: Implement SGX specific hooks in SELinux Cedric Xing
2019-07-09  1:33     ` Sean Christopherson
2019-07-09 21:26       ` Xing, Cedric
2019-07-10 15:49     ` Sean Christopherson
2019-07-10 16:08       ` Jethro Beekman
2019-07-10 18:16         ` Xing, Cedric
2019-07-10 17:54       ` Xing, Cedric
2019-06-27 18:56 ` [RFC PATCH v2 1/3] x86/sgx: Add SGX specific LSM hooks Cedric Xing
2019-06-27 22:06   ` Casey Schaufler
2019-06-27 22:52     ` Xing, Cedric
2019-06-27 23:37       ` Casey Schaufler
2019-06-28  0:47         ` Xing, Cedric
2019-06-28 17:22           ` Casey Schaufler
2019-06-28 22:29             ` Xing, Cedric
2019-06-29  1:37             ` Stephen Smalley
2019-06-29 21:35               ` Casey Schaufler
2019-07-01 17:57                 ` Xing, Cedric
2019-07-01 19:53                   ` Casey Schaufler
2019-07-01 21:45                     ` Xing, Cedric
2019-07-01 23:11                       ` Casey Schaufler
2019-07-02  7:42                         ` Xing, Cedric
2019-07-02 15:44                           ` Casey Schaufler
2019-07-03  9:46                             ` Dr. Greg
2019-07-03 15:32                               ` Casey Schaufler
2019-07-07 13:30                                 ` Dr. Greg
2019-07-09  0:02                                   ` Casey Schaufler
2019-07-09  1:52                                     ` Sean Christopherson
2019-07-09 21:16                                       ` Xing, Cedric
2019-07-11 10:22                                     ` Dr. Greg
2019-07-15 22:23                                       ` Andy Lutomirski
2019-06-28 16:37   ` Stephen Smalley
2019-06-28 21:53     ` Xing, Cedric
2019-06-29  1:22       ` Stephen Smalley
2019-07-01 18:02         ` Xing, Cedric
2019-06-29 23:46   ` Andy Lutomirski
2019-07-01 17:11     ` Xing, Cedric
2019-07-01 17:58       ` Andy Lutomirski
2019-07-01 18:31         ` Xing, Cedric
2019-07-01 19:36           ` Andy Lutomirski
2019-07-01 19:56             ` Xing, Cedric
2019-07-02  2:29               ` Andy Lutomirski
2019-07-02  6:35                 ` Xing, Cedric
2019-06-27 18:56 ` [RFC PATCH v2 2/3] x86/sgx: Call LSM hooks from SGX subsystem/module Cedric Xing
2019-06-27 18:56 ` [RFC PATCH v2 3/3] x86/sgx: Implement SGX specific hooks in SELinux Cedric Xing
2019-07-05 16:05 ` [RFC PATCH v4 00/12] security: x86/sgx: SGX vs. LSM Jarkko Sakkinen
2019-07-08 17:29   ` Sean Christopherson
2019-07-08 17:33     ` Xing, Cedric
2019-07-09 16:22     ` Jarkko Sakkinen
2019-07-09 17:09       ` Sean Christopherson
2019-07-09 20:41         ` Xing, Cedric
2019-07-09 22:25           ` Sean Christopherson
2019-07-09 23:11             ` Xing, Cedric
2019-07-10 16:57               ` Sean Christopherson
2019-07-10 20:19         ` Jarkko Sakkinen
2019-07-10 20:31           ` Sean Christopherson
2019-07-11  9:06             ` Jarkko Sakkinen
2019-07-10 22:00           ` Jarkko Sakkinen
2019-07-10 22:16         ` Jarkko Sakkinen
2019-07-10 23:16           ` Xing, Cedric
2019-07-11  9:26             ` Jarkko Sakkinen
2019-07-11 14:32               ` Stephen Smalley
2019-07-11 17:51                 ` Jarkko Sakkinen
2019-07-12  0:08                   ` Xing, Cedric
2019-07-10  1:28     ` Dr. Greg
2019-07-10  2:04       ` Xing, Cedric
2019-07-10  3:21     ` Jethro Beekman

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