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From: Dave Hansen <dave.hansen@intel.com>
To: Stephen Smalley <sds@tycho.nsa.gov>,
	Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Cedric Xing <cedric.xing@intel.com>,
	James Morris <jmorris@namei.org>,
	"Serge E . Hallyn" <serge@hallyn.com>,
	LSM List <linux-security-module@vger.kernel.org>,
	Paul Moore <paul@paul-moore.com>,
	Eric Paris <eparis@parisplace.org>,
	selinux@vger.kernel.org, Jethro Beekman <jethro@fortanix.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
	linux-sgx@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	nhorman@redhat.com, npmccallum@redhat.com,
	Serge Ayoun <serge.ayoun@intel.com>,
	Shay Katz-zamir <shay.katz-zamir@intel.com>,
	Haitao Huang <haitao.huang@intel.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Kai Svahn <kai.svahn@intel.com>, Borislav Petkov <bp@alien8.de>,
	Josh Triplett <josh@joshtriplett.org>,
	Kai Huang <kai.huang@intel.com>,
	David Rientjes <rientjes@google.com>,
	William Roberts <william.c.roberts@intel.com>,
	Philip Tricca <philip.b.tricca@intel.com>
Subject: Re: [RFC PATCH 8/9] LSM: x86/sgx: Introduce ->enclave_load() hook for Intel SGX
Date: Mon, 3 Jun 2019 11:45:03 -0700	[thread overview]
Message-ID: <4a54f258-425f-fcfb-1ee1-bab138528771@intel.com> (raw)
In-Reply-To: <7fa39363-78ec-8bd3-50e3-b5d05cd4593c@tycho.nsa.gov>

...
>>> What ensures that the mapping referenced by src can't be changed
>>> to an entirely different one (with a different vm_file) between
>>> the time of check (here) and the time of use?
>> 
>> Nothing.  Holding mmap_sem across copy_from_user() would suffice, 
>> correct?
> 
> I don't believe you can do that; copy_from_user() could stall 
> indefinitely.  Not sure how to do what you want here or if it requires
> changing the interface.

Holding mmap_sem for *read* is OK since you can handle page faults
underneath it.  Holding it for write is not.

But, holding it for read also locks out the writers which might be
messing with vm_file or other parts of the VMA.

Holding it for read for a long time is OK.  It's obviously not ideal,
but it is something we do widely today.

  reply	other threads:[~2019-06-03 18:45 UTC|newest]

Thread overview: 77+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-31 23:31 [RFC PATCH 0/9] security: x86/sgx: SGX vs. LSM Sean Christopherson
2019-05-31 23:31 ` [RFC PATCH 1/9] x86/sgx: Remove unused local variable in sgx_encl_release() Sean Christopherson
2019-06-04 11:41   ` Jarkko Sakkinen
2019-05-31 23:31 ` [RFC PATCH 2/9] x86/sgx: Do not naturally align MAP_FIXED address Sean Christopherson
2019-06-04 11:49   ` Jarkko Sakkinen
2019-06-04 20:16     ` Andy Lutomirski
2019-06-04 22:10       ` Xing, Cedric
2019-06-05 14:08         ` Sean Christopherson
2019-06-05 15:17         ` Jarkko Sakkinen
2019-06-05 20:14           ` Andy Lutomirski
2019-06-06 15:37             ` Jarkko Sakkinen
2019-06-13 13:48               ` Jarkko Sakkinen
2019-06-13 16:47                 ` Xing, Cedric
2019-06-13 17:14                   ` Sean Christopherson
2019-06-14 15:18                     ` Jarkko Sakkinen
2019-06-05 15:15       ` Jarkko Sakkinen
2019-05-31 23:31 ` [RFC PATCH 3/9] x86/sgx: Allow userspace to add multiple pages in single ioctl() Sean Christopherson
2019-06-03  6:26   ` Xing, Cedric
2019-06-03 20:08     ` Sean Christopherson
2019-06-03 20:39       ` Sean Christopherson
2019-06-03 23:45         ` Xing, Cedric
2019-06-04  0:54           ` Sean Christopherson
2019-06-04 20:18         ` Andy Lutomirski
2019-06-04 22:02           ` Xing, Cedric
2019-06-03 20:14   ` Dave Hansen
2019-06-03 20:37     ` Sean Christopherson
2019-06-03 20:39       ` Dave Hansen
2019-06-03 23:48       ` Xing, Cedric
2019-06-04  0:55         ` Sean Christopherson
2019-06-04 11:55   ` Jarkko Sakkinen
2019-05-31 23:31 ` [RFC PATCH 4/9] mm: Introduce vm_ops->mprotect() Sean Christopherson
2019-06-03  6:27   ` Xing, Cedric
2019-06-04 12:24   ` Jarkko Sakkinen
2019-06-04 14:51   ` Andy Lutomirski
2019-05-31 23:31 ` [RFC PATCH 5/9] x86/sgx: Restrict mapping without an enclave page to PROT_NONE Sean Christopherson
2019-06-03  6:28   ` Xing, Cedric
2019-06-04 15:32   ` Jarkko Sakkinen
2019-05-31 23:31 ` [RFC PATCH 6/9] x86/sgx: Require userspace to provide allowed prots to ADD_PAGES Sean Christopherson
2019-06-03  6:28   ` Xing, Cedric
2019-06-04 16:23   ` Jarkko Sakkinen
2019-06-04 16:45     ` Sean Christopherson
2019-06-05 15:06       ` Jarkko Sakkinen
2019-06-04 20:23   ` Andy Lutomirski
2019-06-05 11:10   ` Ayoun, Serge
2019-06-05 23:58     ` Sean Christopherson
2019-05-31 23:31 ` [RFC PATCH 7/9] x86/sgx: Enforce noexec filesystem restriction for enclaves Sean Christopherson
2019-06-03  6:29   ` Xing, Cedric
2019-06-04 20:26     ` Andy Lutomirski
2019-06-04 16:25   ` Jarkko Sakkinen
2019-06-04 20:25     ` Andy Lutomirski
2019-06-04 20:34       ` Sean Christopherson
2019-06-04 21:54       ` Xing, Cedric
2019-06-05 15:10       ` Jarkko Sakkinen
2019-06-06  1:01         ` Sean Christopherson
2019-05-31 23:31 ` [RFC PATCH 8/9] LSM: x86/sgx: Introduce ->enclave_load() hook for Intel SGX Sean Christopherson
2019-06-03  6:28   ` Xing, Cedric
2019-06-03 14:19   ` Stephen Smalley
2019-06-03 14:42     ` Sean Christopherson
2019-06-03 18:38       ` Stephen Smalley
2019-06-03 18:45         ` Dave Hansen [this message]
2019-06-04 20:29   ` Andy Lutomirski
2019-06-04 20:36     ` Sean Christopherson
2019-06-04 21:43       ` Xing, Cedric
2019-06-06  2:04         ` Sean Christopherson
2019-05-31 23:31 ` [RFC PATCH 9/9] security/selinux: Add enclave_load() implementation Sean Christopherson
2019-06-03 15:01   ` Stephen Smalley
2019-06-03 15:50     ` Sean Christopherson
2019-06-02  7:29 ` [RFC PATCH 0/9] security: x86/sgx: SGX vs. LSM Xing, Cedric
2019-06-03 17:15   ` Sean Christopherson
2019-06-03 18:30     ` Xing, Cedric
2019-06-04  1:36       ` Sean Christopherson
2019-06-04 15:33       ` Stephen Smalley
2019-06-04 16:30         ` Sean Christopherson
2019-06-04 21:38         ` Xing, Cedric
2019-06-03 17:47   ` Stephen Smalley
2019-06-03 18:02     ` Xing, Cedric
2019-06-04 11:15 ` Jarkko Sakkinen

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