On Fri, 1 Feb 2019, Dave Chinner wrote:
> So, I'll invite the incoherent, incandescent O_DIRECT rage flames of
> Linus to be unleashed again and point out the /other reference/ to
> IOCB_NOWAIT in mm/filemap.c. That is, in generic_file_read_iter(),
> in the *generic O_DIRECT read path*:
>
>
On Thu, Jan 31, 2019 at 11:05 PM Linus Torvalds
wrote:
>
> And part of "best effort" is very much "not a security information leak".
Side note: it's entirely possible that the preadv2(RWF_NOWAIT)
interface is actually already effectively too slow to be effectively
used as much of an attack
On Thu, Jan 31, 2019 at 9:16 PM Dave Chinner wrote:
>
> You are conflating "best effort non-blocking operation" with
> "atomic guarantee". RWF_NOWAIT/IOCB_NOWAIT is the
> former, not the latter.
Right.
That's my *point*, Dave.
It's not 'atomic guarantee", and never will be. We are in 100%
On Thu, Jan 31, 2019 at 09:54:16AM -0800, Linus Torvalds wrote:
> On Thu, Jan 31, 2019 at 2:23 AM Michal Hocko wrote:
> >
> > OK, I guess my question was not precise. What does prevent taking fs
> > locks down the path?
>
> IOCB_NOWAIT has never meant that, and will never mean it.
I think
On Thu, Jan 31, 2019 at 10:56:44AM +0100, Michal Hocko wrote:
> [Cc fs-devel]
>
> On Wed 30-01-19 13:44:19, Vlastimil Babka wrote:
> > From: Jiri Kosina
> >
> > preadv2(RWF_NOWAIT) can be used to open a side-channel to pagecache
> > contents, as
> > it reveals metadata about residency of pages
On Thu, Jan 31, 2019 at 2:23 AM Michal Hocko wrote:
>
> OK, I guess my question was not precise. What does prevent taking fs
> locks down the path?
IOCB_NOWAIT has never meant that, and will never mean it.
We will never give user space those kinds of guarantees. We do locking
for various
On 1/31/19 1:08 PM, Jiri Kosina wrote:
> On Thu, 31 Jan 2019, Daniel Gruss wrote:
>
>> If I understood it correctly, this patch just removes the advantages of
>> preadv2 over mmmap+access for the attacker.
>
> Which is the desired effect. We are not trying to solve the timing aspect,
> as I
On Thu, 31 Jan 2019, Daniel Gruss wrote:
> If I understood it correctly, this patch just removes the advantages of
> preadv2 over mmmap+access for the attacker.
Which is the desired effect. We are not trying to solve the timing aspect,
as I don't think there is a reasonable way to do it, is
On 1/31/19 1:04 PM, Daniel Gruss wrote:
> On 1/30/19 1:44 PM, Vlastimil Babka wrote:
>> Close that sidechannel by always initiating readahead on the cache if we
>> encounter a cache miss for preadv2(RWF_NOWAIT); with that in place, probing
>> the pagecache residency itself will actually populate
On 1/30/19 1:44 PM, Vlastimil Babka wrote:
> Close that sidechannel by always initiating readahead on the cache if we
> encounter a cache miss for preadv2(RWF_NOWAIT); with that in place, probing
> the pagecache residency itself will actually populate the cache, making the
> sidechannel useless.
On Thu, 31 Jan 2019, Florian Weimer wrote:
> >> I think this needs to use a different flag because the semantics are so
> >> much different. If I understand this change correctly, previously,
> >> RWF_NOWAIT essentially avoided any I/O, and now it does not.
> >
> > It still avoid synchronous
On Thu 31-01-19 11:30:24, Jiri Kosina wrote:
> On Thu, 31 Jan 2019, Michal Hocko wrote:
>
> > > > > diff --git a/mm/filemap.c b/mm/filemap.c
> > > > > index 9f5e323e883e..7bcdd36e629d 100644
> > > > > --- a/mm/filemap.c
> > > > > +++ b/mm/filemap.c
> > > > > @@ -2075,8 +2075,6 @@ static ssize_t
* Jiri Kosina:
> On Wed, 30 Jan 2019, Florian Weimer wrote:
>
>> > preadv2(RWF_NOWAIT) can be used to open a side-channel to pagecache
>> > contents, as it reveals metadata about residency of pages in
>> > pagecache.
>> >
>> > If preadv2(RWF_NOWAIT) returns immediately, it provides a clear "page
On Thu, 31 Jan 2019, Michal Hocko wrote:
> > > > diff --git a/mm/filemap.c b/mm/filemap.c
> > > > index 9f5e323e883e..7bcdd36e629d 100644
> > > > --- a/mm/filemap.c
> > > > +++ b/mm/filemap.c
> > > > @@ -2075,8 +2075,6 @@ static ssize_t generic_file_buffered_read(struct
> > > > kiocb *iocb,
> >
On Thu 31-01-19 11:15:28, Jiri Kosina wrote:
> On Thu, 31 Jan 2019, Michal Hocko wrote:
>
> > > diff --git a/mm/filemap.c b/mm/filemap.c
> > > index 9f5e323e883e..7bcdd36e629d 100644
> > > --- a/mm/filemap.c
> > > +++ b/mm/filemap.c
> > > @@ -2075,8 +2075,6 @@ static ssize_t
On Thu, 31 Jan 2019, Michal Hocko wrote:
> > diff --git a/mm/filemap.c b/mm/filemap.c
> > index 9f5e323e883e..7bcdd36e629d 100644
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -2075,8 +2075,6 @@ static ssize_t generic_file_buffered_read(struct
> > kiocb *iocb,
> >
> > page =
[Cc fs-devel]
On Wed 30-01-19 13:44:19, Vlastimil Babka wrote:
> From: Jiri Kosina
>
> preadv2(RWF_NOWAIT) can be used to open a side-channel to pagecache contents,
> as
> it reveals metadata about residency of pages in pagecache.
>
> If preadv2(RWF_NOWAIT) returns immediately, it provides a
On Wed, 30 Jan 2019, Florian Weimer wrote:
> > preadv2(RWF_NOWAIT) can be used to open a side-channel to pagecache
> > contents, as it reveals metadata about residency of pages in
> > pagecache.
> >
> > If preadv2(RWF_NOWAIT) returns immediately, it provides a clear "page
> > not resident"
* Vlastimil Babka:
> preadv2(RWF_NOWAIT) can be used to open a side-channel to pagecache
> contents, as it reveals metadata about residency of pages in
> pagecache.
>
> If preadv2(RWF_NOWAIT) returns immediately, it provides a clear "page
> not resident" information, and vice versa.
>
> Close
From: Jiri Kosina
preadv2(RWF_NOWAIT) can be used to open a side-channel to pagecache contents, as
it reveals metadata about residency of pages in pagecache.
If preadv2(RWF_NOWAIT) returns immediately, it provides a clear "page not
resident" information, and vice versa.
Close that sidechannel
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