On Wed, Oct 28, 2009 at 12:53 PM, Andi Kleen <a...@firstfloor.org> wrote: > Dave Airlie <airl...@gmail.com> writes: > >> They used uint64_t to represent userspace pointers and userspace >> casted into those and the kernel casts back out and passes it to copy_*_user > > uint64_t is actually dangerous due to different alignment on x86-32 vs 64, > better use compat_u64/s64
We've designed that into a/c also, we pad all 64-bit values to 64-bit alignment on all the ioctls we've added to the drm in the past couple of years. Just because of this particular insanity. > >> Now I thought cool I don't need to worry about compat ioctl hackery I can >> run 32 on 64 bit apps fine and it'll all just work. >> >> Now Dave Miller points out that I'm obivously deluded and we really need >> to add compat ioctls so that the kernel can truncate correctly 32-bit address >> in case userspace shoves garbage into the top 32bits of the u64. > > When the user space sees a u64 field it should never shove garbage here. > You just have to cast on 32bit for this, which is a bit ugly. > > However some architectures need special operations on compat pointers > (s390 iirc), but if you don't support those it might be reasonable > to not support that. > >> Is there really no way to avoid compat ioctls? was I delusional in >> thinking there was? > > Experience shows that people make mistakes and you sooner or > later need them anyways to work around them. > Assume no mistakes are made, new ioctls designed from scratch and reviewed to do 32/64-bit properly. The s390 was something I didn't know about but KMS on s390 is probably never going to be something that sees the light of day. I'm just amazed that compat_ioctl should be required for all new code. DrNick on irc suggested just doing: if (is_compat_task()) ptr &= 0x00000000FFFFFFFF; Is there a one liner I can just do in the actual ioctls instead of adding 20 compat ones? Dave. ------------------------------------------------------------------------------ Come build with us! The BlackBerry(R) Developer Conference in SF, CA is the only developer event you need to attend this year. Jumpstart your developing skills, take BlackBerry mobile applications to market and stay ahead of the curve. Join us from November 9 - 12, 2009. Register now! http://p.sf.net/sfu/devconference -- _______________________________________________ Dri-devel mailing list Dri-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/dri-devel
