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Red Hat Introduces NX Software Support For Linux
abertoll writes "In this story at ZDnet, Red Hat has apparently added NX support to Linux. NX security technology is a hardware attempt at stopping malicious code." (We recently posted about Transmeta's announcement that its chips will incorporate the NX bit as well.)
"AMD's Athlon 64 and Opteron processors have had NX since their debut, though the extra bit won't do anything on a Windows XP system until you obtain and install Service Pack 2. Intel is expected to add NX (or XD) to the next generation of its 90-nanometer-process Pentium 4 "Prescott" CPUs -- bundling the security enhancement with a larger 2MB Level 2 cache and perhaps a faster 1066MHz front-side bus -- in the fourth quarter of this year."
This year has truly been AMD's year to guide the microprocessor market. Remember not so far back when everything AMD did was a response to Intel? This year it's been Intel responding to AMD. I hope this trend continues as it shows that the so-called WIntel stranglehold is starting to crack and that it is possible for the competition to assume a leading role in the market. Now hopefully, IBM has something in the works for it's PPC/Power lines, as they've been working closely with AMD and this processor feature is something that every networked system could use.
Right, all AMD K8-class processors have the NX-bit already. And despite the Intel-centric spin on the ZDNet article, the fact is that Intel has only announced that support for it is coming in future Intel parts. Unlike AMD, it doesn't appear you can buy any CPUs from Intel that support the NX bit today.
... written by Andi Kleen". I.e. NX-bit support was already available to AMD64 owners running 64-bit linux kernels.
In other words, Intel is playing catch-up.
And note the comment in Ingo's linux-kernel posting that refers to the "existing NX support in the 64-bit x86_64 kernels
However, true W^X (shorthand for "no segment is both writable and executable") support won't work for applications that depend on self-modifying code, such as JIT-compiling virtual machines for Java and .NET platforms.
data char* temp = new data char[len];
executable char* code = new executable char[len];
int function() = code;
compile(javasrc, temp);
copy(temp, code);
function();
From what I've heard, allocations will default to non-executable, but there will be some sort of API that allows executable space to be allocated on every OS that deals with NX bits. You will probably also see WinXP and the like with the ability to "Run this program in compatibility mode..." until the developer updates to deal with the tweaks made in the updates.
As a long time happy linux user, but also a kernel author (not x86 though, C80), I can't share your positive attitude towards linux on this issue.
Linus sloppily decided to avoid _almost all_ of the protection mechanisms that the 386 makes available to the system. That's why you can smash the stack for fun and profit. He chose to let CS access the same pages as DS (and SS,ES,FS,GS), whe he could have allocated some linear addresses as code-only, and others as data-only. After that you simply need to ensure that no CS ever was given access outside the executable range, and no other segment was given access in the executabe range.
And you can ensure this - as you, the kernel, are entirely in charge of setting up user-space descriptors.
To do so would have added a bit more complexity to the memory management (with lower case letters) part of the kernel, but would have prevented all smash stacking and heap smashing attacks.
Linux is not _technically_ as good OS at all. It's simply _practically_ (for people like me) a good OS.
Tannenbaum is still right. (And when Tannenbaum says "run 20% slower" he means "take up 0.6% of the CPU rather than 0.5% of it, thus giving apps 99.4% of the cpu rather than 99.5%. But that's another rant.)
FP.
Also FatPhil on SoylentNews, id 863