Annotating the kernel to prevent exploits
Annotating the kernel to prevent exploits
Posted Nov 19, 2012 14:39 UTC (Mon) by ebiederm (subscriber, #35028)In reply to: Attacking hardened Linux systems with kernel JIT spraying by cyanit
Parent article: Attacking hardened Linux systems with kernel JIT spraying
The techniques and tools are not yet fully mature. So I would say that is a little more than lack of people caring that has not seen this happen. Especially when you are talking such a large code base.
I was playing with using frama-c which reportedly is one of the better frame works for connecting C code and a prover and it could not handle the C99 of my toy test program. Getting a tool like that to run successfully on the kernel source base with no annotations looks to be a significant undertaking.
Not that this problem is unique to tools like frama-c. Even the clang front end to llvm (an actual production c compiler) has has trouble building the linux kernel.
Posted Nov 19, 2012 22:39 UTC (Mon)
by vonbrand (subscriber, #4458)
[Link] (4 responses)
The seL4 is a microkernel, of which some 7500 lines of C code have been verified rigurously (assuming the compiler and the underlying machine are correct). That is many, many orders of magnitude away from even the most spartan Linux configuration.
Posted Nov 20, 2012 4:26 UTC (Tue)
by pjm (guest, #2080)
[Link] (3 responses)
Even then, so far they only claim to have proven [subject to questionable assumptions such as the compiler conforming to the formalization that they've written themselves] that their C implementation has the same behaviour (and hence same set of bugs) as their implementation in a higher-level language. They haven't claimed to have proven anything (else) about the behaviour of that higher-level-language implementation. So for example, even if the seL4 microkernel contained a JIT compiler, they wouldn't have proven anything about the output of that compiler (to which the kernel presumably passes control while in kernel mode).
OTOH, that program equivalence would certainly reduce the opportunities for exploits (e.g. by ruling out any buffer overflows that don't occur in the higher-level language), and at least it's a bit easier to prove properties of code in a higher-level language than a lower-level one. Mathematical proofs increase confidence, but there's always a gap between a mathematical model and the real world.
Posted Nov 20, 2012 11:45 UTC (Tue)
by Cyberax (✭ supporter ✭, #52523)
[Link] (2 responses)
The next frontier is to prove that hardware itself is correct :)
Posted Nov 20, 2012 13:33 UTC (Tue)
by ebiederm (subscriber, #35028)
[Link] (1 responses)
Hardware design developed formal method for their logic ALUs and FPUs a long time ago. Although that clearly has it's limits. Especially timing.
The next frontier is for program proofs to stop being news and instead partial program proofs increasing program reliability to the point where any program updates except for features become news.
How we go from proofs of concept to useful proof tools is a question I don't yet see answers to.
Posted Nov 20, 2012 19:14 UTC (Tue)
by dlang (guest, #313)
[Link]
Given that people don't even bother to define what acceptable input is, I don't expect this to ever happen.
Not to mention that this would require anticipating all possible internal state, another thing that is not going to happen.
And then you need to have someone think through what should happen in all these combinations of cases, and not have any logic errors in what the 'proofs' are trying to show.
> Hardware design developed formal method for their logic ALUs and FPUs a long time ago. Although that clearly has it's limits. Especially timing.
And when Timing issues dominate, the 'correctness' generated by such proofs is pretty meaningless.
Math is not reality, they sometimes have a resemblance to each other, but that's just a happy coincidence.
Annotating the kernel to prevent exploits
state of the art in formal proofs of kernels
state of the art in formal proofs of kernels
state of the art in formal proofs of kernels
state of the art in formal proofs of kernels