[ Thanks to Bruce
Perens for this link. ]
Update: The story has been pulled with the
following note:
“I’ve withdrawn this article after enough people convinced me that
I didn’t know what I was talking about. It happens sometimes.
Thanks
Bruce”
“Buffer-overflow security exploits are common, but your computer
shouldn’t really be vulnerable to them. It seems the main problem
is with the i386 architecture. Secondary to that, there’s the
problem of operating systems that could protect against this sort
of exploit by using a simple facility of the virtual memory
hardware, but don’t.”
“On processors with an execute-protect bit on their VM pages
and an operating system that uses it properly, buffer-overflow
security bugs can never introduce new executable code into a
process. We can make this facility available in operating systems
like Linux as users transition to processors like Intel’s new ia-64
architecture (also known as Merced or Itanium) and the
ALPHA and MIPS chips. I don’t think any of these chips have
any reason to need the execute bit turned on for stack or data
pages. Rare programs that actually run self-modifying code, like
Java just-in-time compilers and programs that use executable
“trampoline” code on the stack would have to turn off this
protection, but that should be done selectively, on a page-by-page
basis. Linux already has a system call, mprotect(), to do
that.”
“I’m told that someone named “Solar Designer” actually produced
a patch to do this for Linux, but that Linus hasn’t accepted the
patch into the main kernel source. Apparently, there’s even a way
to make it work on the i386, for the stack but not data regions, by
using segmentation instead of paging. I can see why that would
inspire Linus’ esthetic revulsion, even though it’s an important
security fix. Also, someone showed one way to defeat the patch, but
a good many exploits would be stopped dead. The people on the Linux
kernel list, I’m told, have discussed and rejected this idea twice
now. Maybe it’s time for the rest of us to take it more seriously.
There’s also the StackGuard Compiler, which hardens code against
stack attacks and can detect them. We need both of these tools in
our systems.”