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Date: Wed, 28 Oct 2009 11:27:04 +0100 From: Arnd Bergmann <arndbergmann@...glemail.com> To: Andi Kleen <andi@...stfloor.org> Cc: David Miller <davem@...emloft.net>, airlied@...il.com, linux-kernel@...r.kernel.org, dri-devel@...ts.sourceforge.net Subject: Re: is avoiding compat ioctls possible? On Wednesday 28 October 2009, Andi Kleen wrote: > > > 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. > > > > s390 has to sign extend all 32-bit compat process pointers when > > processing them in the 64-bit s390 kernel. I think one other > > architecture has this kind of situation too. > > Which other architure? I reviewed all the definitions in tree > and don't see any other than s390 doing magic there. I'm also pretty sure that s390 is the only one needing this, I added the compat_ptr stuff initially. Note that a cast from pointer to unsigned long to u64 and back in C does the correct 31 to 64 bit extension, which btw is not a sign-extend but a unsigned extend clearing the upper 33 bits. The easier rule to remember should be to always to compat_ptr() on any pointer coming from user space, and to avoid pointers in data structures where possible, as DaveM pointed out. Arnd <>< -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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