Re: [PATCH] nommu arch dont zero the anonymous mapping by adding UNINITIALIZE flag

[Aubrey Li]

On 3/30/07, David Howells <dhowells@xxxxxxxxxx> wrote:
> Aubrey Li <aubreylee@xxxxxxxxx> wrote:
>
> > malloc() allocates size bytes and returns a pointer to the allocated memory.
> > ****The memory is not cleared.****
>
> But this is *not* malloc().  It's mmap().  Are you prepared to guarantee that
> there are no applications out there that don't rely on anon mmap() giving
> zeroed memory?

I can't find mmap must give zeroed memory in the mmap manual.
Is there any reason relying on anon mmap() giving zerod memory?
Can you show me an example?

> The MMU-mode clearing is done for security reasons - there shouldn't be any
> leakage between processes, and because the zero page can just be faulted in.
NO-MMU can't do this clearing. Performance is down.

> Personally, I'd prefer to maintain compatibility with MMU-mode wherever
> possible, but I'm happy with overrides like the MAP_UNINITIALISED flag
> suggested.
Not necessary IMHO.

-Aubrey
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