Messages in this thread |  | | Date | Sun, 10 Dec 2017 13:47:53 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 02/20] torture: Prepare scripting for shift from %p to %pK |
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On Sun, Dec 10, 2017 at 12:39:11PM -0800, Linus Torvalds wrote: > On Sun, Dec 10, 2017 at 4:52 AM, Andy Shevchenko > <andy.shevchenko@gmail.com> wrote: > >> > >>> Perhaps it should have printed a fixed, non-zero value for non-zero > >>> pointers. > >> > >> I must leave this to the people who have a dog in that contest. ;-) > > > > Since there is an ongoing discussion with security people near to %pK > > and alike, I added Kees and Linus to Cc list. > > > > The proposed change can be done easily, though I have no knowledge > > about possible implications. > > I'd rather make %pK act more like %p than have gratuitous differences. > > I also think %pK is kind of pointless in general. It has not been a > big success, and the whole "root or not" is kind of nasty anyway. Root > in a container? Things like that. > > So I think that if people worry about leaking pointers, they should > primarily go for: > > - just use %p and now get the hashed value > > - if the hashed value is pointless, ask yourself whether the pointer > itself is important. Maybe it should be removed? > > - as a last option, if you really think the true pointer value is > important, why is root so special, and maybe you should use %px and > make sure you have proper sensible permissions. > > ..and %pK just isn't really the answer in any of those cases.
My main use case is comparing pointer values directly, for example, in the console log against those in event-trace output. So if those are hashed the same way, I wouldn't even notice.
I very rarely need to compute offsets, but I thought that the low-order bits were excluded from the hash to make this work straightforwardly in the common case. Of course, computing offsets could be a problem for larger structures, by my reaction to that would be to make the kernel do the offset computation for me as needed.
So it looks like I should drop the three patches in my tree that convert %p to %pK.
Any objections?
Thanx, Paul
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