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    SubjectRe: [PATCH v9 1/4] syscalls: Verify address limit before returning to user-mode

    * Kees Cook <keescook@chromium.org> wrote:

    > > And yes, I realize that there were other such bugs and that such bugs might
    > > occur in the future - but why not push the overhead of the security check to
    > > the kernel build phase? I.e. I'm wondering how well we could do static
    > > analysis during kernel build - would a limited mode of Sparse be good enough
    > > for that? Or we could add a new static checker to tools/, built from first
    > > principles and used primarily for extended syntactical checking.
    >
    > Static analysis is just not going to cover all cases. We've had vulnerabilities
    > where interrupt handlers left KERNEL_DS set, for example. [...]

    Got any commit ID of that bug - was it because a function executed by the
    interrupt handler leaked KERNEL_DS?

    > [...] If there are performance concerns, let's put this behind a CONFIG. 2-5
    > instructions is not an issue for most people that want this coverage.

    That doesn't really _solve_ the performance concerns, it just forces most people
    to enable it by creating a 'security or performance' false dichotomy ...

    > [...] and it still won't catch everything. Bug-finding is different from making
    > a bug class just unexploitable at all. As we've done before, it's the difference
    > between trying to find format string attacks vs just removing %n from the format
    > parser.

    No, it does not make it unexploitable, it could still be exploitable if the
    runtime check is buggy or if there's kernel execution outside of the regular
    system call paths - there's plenty of such hardware functionality on x86 for
    example.

    Thanks,

    Ingo

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