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    SubjectRe: [PATCH v2] kptr_restrict for hiding kernel pointers from unprivileged users
    On Fri, 10 Dec 2010 19:05:24 -0500
    Dan Rosenberg <drosenberg@vsecurity.com> wrote:

    > + case 'K':
    > + if (kptr_restrict) {
    > + if (in_irq() || in_serving_softirq() || in_nmi())
    > + WARN(1, "%%pK used in interrupt context.\n");
    > +
    > + else if (capable(CAP_SYSLOG))
    > + break;
    > +
    > + if (spec.field_width == -1) {
    > + spec.field_width = 2 * sizeof(void *);
    > + spec.flags |= ZEROPAD;
    > + }
    > + return number(buf, end, 0, spec);
    > + }
    > + break;

    Also, we should emit the runtime warning even if kptr_restrict is
    false. Otherwise programmers might ship buggy code because they didn't
    enable kptr_restrict during testing.

    So what I ended up with was

    case 'K':
    /*
    * %pK cannot be used in IRQ context because it tests
    * CAP_SYSLOG.
    */
    if (in_irq() || in_serving_softirq() || in_nmi())
    WARN_ONCE(1, "%%pK used in interrupt context.\n");

    if (!kptr_restrict)
    break; /* %pK does not obscure pointers */

    if (capable(CAP_SYSLOG))
    break; /* privileged apps expose pointers */

    if (spec.field_width == -1) {
    spec.field_width = 2 * sizeof(void *);
    spec.flags |= ZEROPAD;
    }
    return number(buf, end, 0, spec);

    How does that look?


    Also... permitting root to bypass the %pK obscuring seems pretty lame,
    really. I bet a *lot* of the existing %p sites are already root-only
    (eg, driver initialisation). So much of the value is lost.


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