Messages in this thread | | | Subject | Re: [PATCH] sys_getppid oopses on debug kernel | From | Andi Kleen <> | Date | 09 Aug 2006 05:09:11 +0200 |
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Kirill Korotaev <dev@sw.ru> writes:
[adding linux-arch]
> > Accessing freed memory is a bug, always, not just *only* when slab > > debugging is on, right? Doesn't this mean we could get junk, or that > > the reader could potentially run off a bad pointer? > no, read the comment in sys_getppid. > It is a valid optimization. _safe_ and alowing to bypass taking the lock. > BUT! This optimization relies on the fact that kernel memory (DMA + normal zone) > is always mapped into virtual address space. > Which is invalid for debug kernels only.
In x86 arch code we would use __get_user for this (and we do in a couple of places). But it wouldn't be portable because sometimes _user is in a different address space.
Maybe it would be time to make a similar facility (read/write_kernel_safe() or similar) with error return available to generic code?
It should be easy to implement - iirc near all architectures already use the exception handling frame work and it is a simple extension of that. x86 could just define it to __put/get_user
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