From: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: x86@kernel.org, linux-sgx@vger.kernel.org,
linux-kernel@vger.kernel.org,
linux-security-module@vger.kernel.org, linux-mm@kvack.org,
Andrew Morton <akpm@linux-foundation.org>,
Jethro Beekman <jethro@fortanix.com>,
Haitao Huang <haitao.huang@linux.intel.com>,
Chunyang Hui <sanqian.hcy@antfin.com>,
Jordan Hand <jorhand@linux.microsoft.com>,
Nathaniel McCallum <npmccallum@redhat.com>,
Seth Moore <sethmo@google.com>,
Darren Kenny <darren.kenny@oracle.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Suresh Siddha <suresh.b.siddha@intel.com>,
andriy.shevchenko@linux.intel.com, asapek@google.com,
bp@alien8.de, cedric.xing@intel.com, chenalexchen@google.com,
conradparker@google.com, cyhanish@google.com,
dave.hansen@intel.com, haitao.huang@intel.com,
kai.huang@intel.com, kai.svahn@intel.com, kmoy@google.com,
ludloff@google.com, luto@kernel.org, nhorman@redhat.com,
puiterwijk@redhat.com, rientjes@google.com, tglx@linutronix.de,
yaozhangx@google.com, mikko.ylinen@intel.com
Subject: Re: [PATCH v39 11/24] x86/sgx: Add SGX enclave driver
Date: Mon, 5 Oct 2020 00:50:49 +0300 [thread overview]
Message-ID: <20201004215049.GA43926@linux.intel.com> (raw)
In-Reply-To: <20201003195440.GD20115@casper.infradead.org>
On Sat, Oct 03, 2020 at 08:54:40PM +0100, Matthew Wilcox wrote:
> On Sat, Oct 03, 2020 at 07:50:46AM +0300, Jarkko Sakkinen wrote:
> > + XA_STATE(xas, &encl->page_array, idx_start);
> > +
> > + /*
> > + * Disallow READ_IMPLIES_EXEC tasks as their VMA permissions might
> > + * conflict with the enclave page permissions.
> > + */
> > + if (current->personality & READ_IMPLIES_EXEC)
> > + return -EACCES;
> > +
> > + xas_for_each(&xas, page, idx_end)
> > + if (!page || (~page->vm_max_prot_bits & vm_prot_bits))
> > + return -EACCES;
>
> You're iterating the array without holding any lock that the XArray knows
> about. If you're OK with another thread adding/removing pages behind your
> back, or there's a higher level lock (the mmap_sem?) protecting the XArray
> from being modified while you walk it, then hold the rcu_read_lock()
> while walking the array. Otherwise you can prevent modification by
> calling xas_lock(&xas) and xas_unlock()..
I backtracked this. The locks have been there from v21-v35. This is a
refactoring mistake in radix_tree to xarray migration happened in v36.
It's by no means intentional.
What is shoukd take is encl->lock.
The loop was pre-v36 like:
idx_start = PFN_DOWN(start);
idx_end = PFN_DOWN(end - 1);
for (idx = idx_start; idx <= idx_end; ++idx) {
mutex_lock(&encl->lock);
page = radix_tree_lookup(&encl->page_tree, idx);
mutex_unlock(&encl->lock);
if (!page || (~page->vm_max_prot_bits & vm_prot_bits))
return -EACCES;
}
Looking at xarray.h and filemap.c, I'm thinking something along the
lines of:
for (idx = idx_start; idx <= idx_end; ++idx) {
mutex_lock(&encl->lock);
page = xas_find(&xas, idx + 1);
mutex_unlock(&encl->lock);
if (!page || (~page->vm_max_prot_bits & vm_prot_bits))
return -EACCES;
}
Does this look about right?
/Jarkko
next prev parent reply other threads:[~2020-10-04 21:51 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20201003045059.665934-1-jarkko.sakkinen@linux.intel.com>
2020-10-03 4:50 ` [PATCH v39 10/24] mm: Add 'mprotect' hook to struct vm_operations_struct Jarkko Sakkinen
2020-10-03 4:50 ` [PATCH v39 11/24] x86/sgx: Add SGX enclave driver Jarkko Sakkinen
2020-10-03 14:39 ` Greg KH
2020-10-04 14:32 ` Jarkko Sakkinen
2020-10-04 15:01 ` Jarkko Sakkinen
2020-10-05 9:42 ` Greg KH
2020-10-05 12:42 ` Jarkko Sakkinen
2020-10-07 18:09 ` Haitao Huang
2020-10-07 19:26 ` Greg KH
2020-10-09 6:44 ` Jarkko Sakkinen
2020-10-14 20:16 ` Dave Hansen
2020-10-05 8:45 ` Christoph Hellwig
2020-10-05 11:42 ` Jarkko Sakkinen
2020-10-05 11:50 ` Greg KH
2020-10-05 14:23 ` Jarkko Sakkinen
2020-10-05 15:02 ` Greg KH
2020-10-05 16:40 ` Dave Hansen
2020-10-05 20:02 ` Jarkko Sakkinen
2020-10-09 7:10 ` Pavel Machek
2020-10-09 7:21 ` Greg KH
2020-10-09 8:21 ` Pavel Machek
2020-10-03 19:54 ` Matthew Wilcox
2020-10-04 21:50 ` Jarkko Sakkinen [this message]
2020-10-04 22:02 ` Jarkko Sakkinen
2020-10-04 22:27 ` Matthew Wilcox
2020-10-04 23:41 ` Jarkko Sakkinen
2020-10-05 1:30 ` Matthew Wilcox
2020-10-05 3:06 ` Jarkko Sakkinen
2020-10-03 4:50 ` [PATCH v39 16/24] x86/sgx: Add a page reclaimer Jarkko Sakkinen
2020-10-03 5:22 ` Haitao Huang
2020-10-03 13:32 ` Jarkko Sakkinen
2020-10-03 18:23 ` Haitao Huang
2020-10-04 22:39 ` Jarkko Sakkinen
2020-10-07 17:25 ` Jarkko Sakkinen
2020-10-03 4:50 ` [PATCH v39 17/24] x86/sgx: Add ptrace() support for the SGX driver Jarkko Sakkinen
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