Messages in this thread | | | Date | Thu, 24 Jul 2008 16:02:43 -0700 | From | Suresh Siddha <> | Subject | Re: [patch] x64, fpu: fix possible FPU leakage in error conditions |
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On Thu, Jul 24, 2008 at 03:43:44PM -0700, Linus Torvalds wrote: > > > On Thu, 24 Jul 2008, Suresh Siddha wrote: > > > > > > but the thing is, the only really valid reason for "restore_i387()" to > > > fail is because the read failed. > > > > Not really. It can cause #GP, if someone sets reserved bits of mxcsr > > in the memory image. > > Ahh, ok, I can imagine that. And I guess we might copy the data from user > space into the memory image without validating it at points (signal > handler restore and/or ptrace). Do we?
Today in ptrace (and in 32bit signal handling), we copy the user data and then clear the reserved bits blindly again ;)
In 64bit signal handling, we do a fxrstor from the live user buffer and scream then itself if we find an issue.
Andi being paranoid, added more checks for 64bit math_state_restore().
> > But restore_i387() may be in an insane state (we did clts() but doesn't > > have the proper state in its live registers etc) when it failed to restore fpu. > > Ideally we should fix this inside restore_i387(). But restore_i387() > > is in header file and I have to re-arrange some of the code > > in the header file, to call clear_fpu() from restore_i387(). > > Ok, how about we just move restore_i387() out of the header file? I > realize that the x86 code plays some games with this whole thing (that > whole '#define restore_i387_ia32 restore_i387'), but that is 32-bit > specific, and the restore_i387() in the header file is 64-bit specific. > > Hmm. In fact, I think that x86-64 version is actually only used in a > single place - arch/x86/kernel/signal_64.c. So it's actively *wrong* to > have that thing in a header file to begin with! > > So how about this patch as a starting point? This is the RightThing(tm) to > do regardless, and if it then makes it easier to do some other cleanups, > we should do it first. What do you think?
Sure. You have my Ack. I will request -stable folks to pickup multiple patches (second patch, I will post shortly on top of yours).
thanks, suresh
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