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From: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
To: Fuad Tabba <tabba@google.com>
Cc: Chao Peng <chao.p.peng@linux.intel.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
	linux-api@vger.kernel.org, linux-doc@vger.kernel.org,
	qemu-devel@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
	Hugh Dickins <hughd@google.com>, Jeff Layton <jlayton@kernel.org>,
	"J . Bruce Fields" <bfields@fieldses.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Shuah Khan <shuah@kernel.org>, Mike Rapoport <rppt@kernel.org>,
	Steven Price <steven.price@arm.com>,
	"Maciej S . Szmigiero" <mail@maciej.szmigiero.name>,
	Vlastimil Babka <vbabka@suse.cz>,
	Vishal Annapurve <vannapurve@google.com>,
	Yu Zhang <yu.c.zhang@linux.intel.com>,
	luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com,
	ak@linux.intel.com, david@redhat.com, aarcange@redhat.com,
	ddutile@redhat.com, dhildenb@redhat.com,
	Quentin Perret <qperret@google.com>,
	Michael Roth <michael.roth@amd.com>,
	mhocko@suse.com, Muchun Song <songmuchun@bytedance.com>,
	wei.w.wang@intel.com
Subject: Re: [PATCH v8 1/8] mm/memfd: Introduce userspace inaccessible memfd
Date: Fri, 30 Sep 2022 19:23:01 +0300	[thread overview]
Message-ID: <20220930162301.i226o523teuikygq@box.shutemov.name> (raw)
In-Reply-To: <CA+EHjTyrexb_LX7Jm9-MGwm4DBvfjCrADH4oumFyAvs2_0oSYw@mail.gmail.com>

On Fri, Sep 30, 2022 at 05:14:00PM +0100, Fuad Tabba wrote:
> Hi,
> 
> <...>
> 
> > diff --git a/mm/memfd_inaccessible.c b/mm/memfd_inaccessible.c
> > new file mode 100644
> > index 000000000000..2d33cbdd9282
> > --- /dev/null
> > +++ b/mm/memfd_inaccessible.c
> > @@ -0,0 +1,219 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +#include "linux/sbitmap.h"
> > +#include <linux/memfd.h>
> > +#include <linux/pagemap.h>
> > +#include <linux/pseudo_fs.h>
> > +#include <linux/shmem_fs.h>
> > +#include <uapi/linux/falloc.h>
> > +#include <uapi/linux/magic.h>
> > +
> > +struct inaccessible_data {
> > +       struct mutex lock;
> > +       struct file *memfd;
> > +       struct list_head notifiers;
> > +};
> > +
> > +static void inaccessible_notifier_invalidate(struct inaccessible_data *data,
> > +                                pgoff_t start, pgoff_t end)
> > +{
> > +       struct inaccessible_notifier *notifier;
> > +
> > +       mutex_lock(&data->lock);
> > +       list_for_each_entry(notifier, &data->notifiers, list) {
> > +               notifier->ops->invalidate(notifier, start, end);
> > +       }
> > +       mutex_unlock(&data->lock);
> > +}
> > +
> > +static int inaccessible_release(struct inode *inode, struct file *file)
> > +{
> > +       struct inaccessible_data *data = inode->i_mapping->private_data;
> > +
> > +       fput(data->memfd);
> > +       kfree(data);
> > +       return 0;
> > +}
> > +
> > +static long inaccessible_fallocate(struct file *file, int mode,
> > +                                  loff_t offset, loff_t len)
> > +{
> > +       struct inaccessible_data *data = file->f_mapping->private_data;
> > +       struct file *memfd = data->memfd;
> > +       int ret;
> > +
> > +       if (mode & FALLOC_FL_PUNCH_HOLE) {
> > +               if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))
> > +                       return -EINVAL;
> > +       }
> > +
> > +       ret = memfd->f_op->fallocate(memfd, mode, offset, len);
> 
> I think that shmem_file_operations.fallocate is only set if
> CONFIG_TMPFS is enabled (shmem.c). Should there be a check at
> initialization that fallocate is set, or maybe a config dependency, or
> can we count on it always being enabled?

It is already there:

	config MEMFD_CREATE
		def_bool TMPFS || HUGETLBFS

And we reject inaccessible memfd_create() for HUGETLBFS.

But if we go with a separate syscall, yes, we need the dependency.

> > +       inaccessible_notifier_invalidate(data, offset, offset + len);
> > +       return ret;
> > +}
> > +
> 
> <...>
> 
> > +void inaccessible_register_notifier(struct file *file,
> > +                                   struct inaccessible_notifier *notifier)
> > +{
> > +       struct inaccessible_data *data = file->f_mapping->private_data;
> > +
> > +       mutex_lock(&data->lock);
> > +       list_add(&notifier->list, &data->notifiers);
> > +       mutex_unlock(&data->lock);
> > +}
> > +EXPORT_SYMBOL_GPL(inaccessible_register_notifier);
> 
> If the memfd wasn't marked as inaccessible, or more generally
> speaking, if the file isn't a memfd_inaccessible file, this ends up
> accessing an uninitialized pointer for the notifier list. Should there
> be a check for that here, and have this function return an error if
> that's not the case?

I think it is "don't do that" category. inaccessible_register_notifier()
caller has to know what file it operates on, no?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

  reply	other threads:[~2022-09-30 16:24 UTC|newest]

Thread overview: 97+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-15 14:29 [PATCH v8 0/8] KVM: mm: fd-based approach for supporting KVM Chao Peng
2022-09-15 14:29 ` [PATCH v8 1/8] mm/memfd: Introduce userspace inaccessible memfd Chao Peng
2022-09-19  9:12   ` David Hildenbrand
2022-09-19 19:10     ` Sean Christopherson
2022-09-21 21:10       ` Andy Lutomirski
2022-09-22 13:23         ` Wang, Wei W
2022-09-23 15:20         ` Fuad Tabba
2022-09-23 15:19       ` Fuad Tabba
2022-09-26 14:23         ` Chao Peng
2022-09-26 15:51           ` Fuad Tabba
2022-09-27 22:47             ` Sean Christopherson
2022-09-30 16:19               ` Fuad Tabba
2022-10-13 13:34                 ` Chao Peng
2022-10-17 10:31                   ` Fuad Tabba
2022-10-17 14:58                     ` Chao Peng
2022-10-17 19:05                       ` Fuad Tabba
2022-10-19 13:30                         ` Chao Peng
2022-10-18  0:33                 ` Sean Christopherson
2022-10-19 15:04                   ` Fuad Tabba
2022-09-23  0:58     ` Kirill A . Shutemov
2022-09-26 10:35       ` David Hildenbrand
2022-09-26 14:48         ` Kirill A. Shutemov
2022-09-26 14:53           ` David Hildenbrand
2022-09-27 23:23             ` Sean Christopherson
2022-09-28 13:36               ` Kirill A. Shutemov
2022-09-22 13:26   ` Wang, Wei W
2022-09-22 19:49     ` Sean Christopherson
2022-09-23  0:53       ` Kirill A . Shutemov
2022-09-23 15:20         ` Fuad Tabba
2022-09-30 16:14   ` Fuad Tabba
2022-09-30 16:23     ` Kirill A . Shutemov [this message]
2022-10-03  7:33       ` Fuad Tabba
2022-10-03 11:01         ` Kirill A. Shutemov
2022-10-04 15:39           ` Fuad Tabba
2022-10-06  8:50   ` Fuad Tabba
2022-10-06 13:04     ` Kirill A. Shutemov
2022-10-17 13:00   ` Vlastimil Babka
2022-10-17 16:19     ` Kirill A . Shutemov
2022-10-17 16:39       ` Gupta, Pankaj
2022-10-17 21:56         ` Kirill A . Shutemov
2022-10-18 13:42           ` Vishal Annapurve
2022-10-19 15:32             ` Kirill A . Shutemov
2022-10-20 10:50               ` Vishal Annapurve
2022-10-21 13:54                 ` Chao Peng
2022-10-21 16:53                   ` Sean Christopherson
2022-10-19 12:23   ` Vishal Annapurve
2022-10-21 13:47     ` Chao Peng
2022-10-21 16:18       ` Sean Christopherson
2022-10-24 14:59         ` Kirill A . Shutemov
2022-10-24 15:26           ` David Hildenbrand
2022-11-03 16:27           ` Vishal Annapurve
2022-09-15 14:29 ` [PATCH v8 2/8] KVM: Extend the memslot to support fd-based private memory Chao Peng
2022-09-16  9:14   ` Bagas Sanjaya
2022-09-16  9:53     ` Chao Peng
2022-09-26 10:26   ` Fuad Tabba
2022-09-26 14:04     ` Chao Peng
2022-09-29 22:45   ` Isaku Yamahata
2022-09-29 23:22     ` Sean Christopherson
2022-10-05 13:04   ` Jarkko Sakkinen
2022-10-05 22:05     ` Jarkko Sakkinen
2022-10-06  9:00   ` Fuad Tabba
2022-10-06 14:58   ` Jarkko Sakkinen
2022-10-06 15:07     ` Jarkko Sakkinen
2022-10-06 15:34       ` Sean Christopherson
2022-10-07 11:14         ` Jarkko Sakkinen
2022-10-07 14:58           ` Sean Christopherson
2022-10-07 21:54             ` Jarkko Sakkinen
2022-10-08 16:15               ` Jarkko Sakkinen
2022-10-08 17:35                 ` Jarkko Sakkinen
2022-10-10  8:25                   ` Chao Peng
2022-10-12  8:14                     ` Jarkko Sakkinen
2022-09-15 14:29 ` [PATCH v8 3/8] KVM: Add KVM_EXIT_MEMORY_FAULT exit Chao Peng
2022-09-16  9:17   ` Bagas Sanjaya
2022-09-16  9:54     ` Chao Peng
2022-09-15 14:29 ` [PATCH v8 4/8] KVM: Use gfn instead of hva for mmu_notifier_retry Chao Peng
2022-09-15 14:29 ` [PATCH v8 5/8] KVM: Register/unregister the guest private memory regions Chao Peng
2022-09-26 10:36   ` Fuad Tabba
2022-09-26 14:07     ` Chao Peng
2022-10-11  9:48   ` Fuad Tabba
2022-10-12  2:35     ` Chao Peng
2022-10-17 10:15       ` Fuad Tabba
2022-10-17 22:17         ` Sean Christopherson
2022-10-19 13:23           ` Chao Peng
2022-10-19 15:02             ` Fuad Tabba
2022-10-19 16:09               ` Sean Christopherson
2022-10-19 18:32                 ` Fuad Tabba
2022-09-15 14:29 ` [PATCH v8 6/8] KVM: Update lpage info when private/shared memory are mixed Chao Peng
2022-09-29 16:52   ` Isaku Yamahata
2022-09-30  8:59     ` Chao Peng
2022-09-15 14:29 ` [PATCH v8 7/8] KVM: Handle page fault for private memory Chao Peng
2022-10-14 18:57   ` Sean Christopherson
2022-10-17 14:48     ` Chao Peng
2022-09-15 14:29 ` [PATCH v8 8/8] KVM: Enable and expose KVM_MEM_PRIVATE Chao Peng
2022-10-04 14:55   ` Jarkko Sakkinen
2022-10-10  8:31     ` Chao Peng
2022-10-06  8:55   ` Fuad Tabba
2022-10-10  8:33     ` Chao Peng

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