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    SubjectRe: [PATCH 3/6] x86/dumpstack: make printk_stack_address() more generally useful
    On Thu, Aug 25, 2016 at 11:12:40PM -0700, Linus Torvalds wrote:
    > On Aug 25, 2016 10:57 PM, "Josh Poimboeuf" <jpoimboe@redhat.com> wrote:
    > >
    > > But I still don't quite understand your statement that dmesg_restrict is
    > > only useful for locked down systems.
    > >
    > > To prevent kernel address disclosure, it seems we already rely on the
    > > user setting kptr_restrict today, otherwise I can do cat
    > > /proc/self/stack and the game is already lost, right?
    >
    > The point is: kptr_restrict actually makes sense, and is widely useful. It
    > doesn't really end up hurting normal things. It's a pretty targeted thing,
    > and generally doesn't actually hurt. You can still do basic health
    > monitoring without having to get elevated privileges, for example.
    >
    > Even system maintainers don't want to be root all the time. In fact, I
    > suspect that the better a system maintainer you are, the less you want to
    > be root - but you'll still want to see logs etc.
    >
    > So note the difference between kptr_restrict and dmesg_restrict.
    >
    > One is useful in a pretty wide environment, the other simply is not.
    >
    > > So what's the difference between expecting the user to set kptr_restrict
    > > vs dmesg_restrict?
    >
    > Do you see the difference now?
    >
    > kptr_restrict simply doesn't hurt as much as dmesg_restrict, so you can
    > enable it fairly widely by default.
    >
    > That makes it the *much* better security option. Because security options
    > that you can't enable aren't actually useful.

    Yeah, at least for human-administered systems, that does make sense.
    Grumpy sysadmins don't want to type "sudo dmesg" or "sudo journalctl"
    because a) they don't like change; and b) using sudo adds risk.

    And a security option which is never used is indeed useless. So *maybe*
    that's a good enough argument for expecting the user to only enable
    kptr_restrict instead of both.

    But with cloud, devops, mobile, embedded, IoT, [insert buzzword], it
    seems most systems are actually managed by software nowadays. Then the
    above arguments don't seem to apply, and dmesg_restrict could still be
    quite widely useful, no?

    --
    Josh

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