Linux 2.6.30 exploit posted [LWN.net]

Linux 2.6.30 exploit posted

Posted Jul 24, 2009 20:44 UTC (Fri) by nix (subscriber, #2304)
In reply to: Linux 2.6.30 exploit posted by kubarebo
Parent article: Linux 2.6.30 exploit posted

GCC isn't ever going to compile code for platforms with only 256 bytes of
RAM. It's always been targetted at systems larger than that.

The C Standard disagrees that it's up to the developer to ensure a pointer
is valid: it doesn't just ban null pointers but also things like dividing
pointers by two, XORing pointers, shoving pointers off the ends of arrays
and so on. Attempting to dictate the semantics of pointers in these
situations would be catastrophic for optimization: even simple code motion
would probably have to be banned.

A simple flag (and a target flag) that says 'this compilation
specifically/this target usually has nonfaulting accesses to (void *)0' is
all that's needed, and we have that already.

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Linux 2.6.30 exploit posted

Posted Apr 13, 2011 17:23 UTC (Wed) by Blaisorblade (guest, #25465) [Link]

I agree that the flag is enough.
Anyway, IIRC, by the C standard (6.5.8.5), comparing pointers to different objects gives rise to undefined behavior, while in C++ it gives an unspecified result [1]. Therefore, while it would be valid for GCC (in C) to produce a crashing program, it would be probably of little use.

[1] http://stackoverflow.com/questions/4909766/is-it-unspecif...