Andi Kleen wrote:
On Tuesday 08 November 2005 05:39, Zachary Amsden wrote:
IA-32 linear address translation is loads of fun.
Thanks for doing that audit work. Can you please double check x86-64 code is
ok?
Actually giving all that complexity maybe it would be better to just
stop handling the case and remove all that. I'm not sure what kprobes needs it
for - it doesn't even handle user space yet and even if it ever does it is
unlikely that handling 16bit code makes much sense. And the prefetch
workaround does it, but 16bit DOS code is unlikely to contain prefetches
anyways. And for ptrace - well, who cares? I suppose dosemu has an own
debugger anyways and it could be handled in user space (i suppose
they still have that code from 2.4 anyways)
I got the idea from the x86-64 code; prompted by you, I looked at it,
and it appears correct, but I would like to give it a full audit as well
(especially regarding 32-bit compatibility segments).
About the three cases here:
The prefetch workaround should be harmless, again because of limit
checking, the kernel is safe even in the raceful cases.
One can imagine clever uses for ptrace to do, say user space
virtualization (since I'm on the topic), or other neat things. So there
is nothing really wrong about having the fully correct EIP conversion
(and here we shouldn't need to worry about races causing some issues
with strict correctness, since there can be one external control thread).
But were kprobes even inteneded for userspace? There are races here
that are difficult to close without some heavy machinery, and I would
rather not put the machinery in place if simplifying the code is the
right answer.
Zach
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