Re: [PATCH v3 0/6] kernel: introduce uaccess logging

On Wed, Dec 8, 2021 at 7:33 AM Marco Elver [off-list ref] wrote:

On Wed, 8 Dec 2021 at 05:48, Peter Collingbourne [off-list ref] wrote:
[...]

quoted

Peter Collingbourne (6):
  include: split out uaccess instrumentation into a separate header
  uaccess-buffer: add core code
  fs: use copy_from_user_nolog() to copy mount() data
  uaccess-buffer: add CONFIG_GENERIC_ENTRY support
  arm64: add support for uaccess logging
  Documentation: document uaccess logging

I think it needs to be possible to disable the feature via a Kconfig
option. Not all systems want or could even tolerate the additional
overheads -- even though you say they are minimal elsewhere. For
example, some embedded systems most likely have absolutely no use for
this feature, and the increase in .text might be unacceptable. Certain
features that we usually take for granted are no different (see
init/Kconfig: FUTEX, EPOLL, .. etc). If you'd like it enabled by
default, given the overheads are small enough, it can do "default y"
and be configurable only "if EXPERT".

Okay, done.

Is it possible to add a kselftest-style test to
tools/testing/selftests? In addition to the basic tests, can certain
non-trivial properties, like masking of signals, also be tested? I
think that'd be extremely valuable, because I'm sure we'd have to
backport this to several older kernels.

Yes, I've added a new patch with a kselftest. (Good thing I did,
because it (together with DEBUG_PREEMPT) uncovered a bug in the
pre/post-exit-loop code. Fixed in v4.)

Peter

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