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SubjectRe: [PATCH v6 0/7] Kernel base address randomization

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

> Here is the latest version of the kASLR series. It has much improved
> e820 walking code, and expands the window available on 64-bit.
>
> This is rolled out on Chrome OS devices, and working well.

There's one kernel debuggability detail that should be discussed I think:
should symbolic printouts (in oops messages but also in /proc/kallsyms)
and instrumentation interfaces that expose kernel addresses attempt to
de-randomize the addresses, stack contents and register values that lie
within the random range?

- it would be easier to use those addresses and look them up in a vmlinux
or in a System.map as well.

- it would be somewhat safer to post an oops publicly if it did not
contain the random offset in an easily identifiable way.

- oops patterns from distribution kernels that enable randomization would
match up better.

- this would make it safer to expose /proc/kallsyms to user-space
profiling, while keeping the random offset a kernel-internal secret.

- RIP information in profiling streams would thus not contain the
kernel random offset either.

The other approach would be what your series does, to keep all the raw,
randomized output and to assume that users who are allowed to access to
logs or profiling can learn the random offset.

I tend to lean towards the 'raw' approach that you picked, but an argument
can be made for both approaches - and in any case I haven't seen this
discussed to conclusion with cons/pros listed and a consensus/decision
reached.

Thanks,

Ingo


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