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kernel: add panic_on_taint

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Analogously to the introduction of panic_on_warn, this patch introduces
a kernel option named panic_on_taint in order to provide a simple and
generic way to stop execution and catch a coredump when the kernel gets
tainted by any given flag.

This is useful for debugging sessions as it avoids having to rebuild the
kernel to explicitly add calls to panic() into the code sites that
introduce the taint flags of interest.

For instance, if one is interested in proceeding with a post-mortem
analysis at the point a given code path is hitting a bad page (i.e.
unaccount_page_cache_page(), or slab_bug()), a coredump can be collected
by rebooting the kernel with 'panic_on_taint=0x20' amended to the
command line.

Another, perhaps less frequent, use for this option would be as a means
for assuring a security policy case where only a subset of taints, or no
single taint (in paranoid mode), is allowed for the running system.  The
optional switch 'nousertaint' is handy in this particular scenario, as
it will avoid userspace induced crashes by writes to sysctl interface
/proc/sys/kernel/tainted causing false positive hits for such policies.

[akpm@linux-foundation.org: tweak kernel-parameters.txt wording]

Suggested-by: Qian Cai <cai@lca.pw>
Signed-off-by: Rafael Aquini <aquini@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Cc: Dave Young <dyoung@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kees Cook <keescook@chromium.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Adrian Bunk <bunk@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Jeff Mahoney <jeffm@suse.com>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Takashi Iwai <tiwai@suse.de>
Link: http://lkml.kernel.org/r/20200515175502.146720-1-aquini@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rafael Aquini
2020-06-07 21:40:17 -07:00
committed by Linus Torvalds
parent ceabef7dd7
commit db38d5c106
6 changed files with 75 additions and 1 deletions
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7
Documentation/admin-guide/sysctl/kernel.rst
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@ -1239,6 +1239,13 @@ ORed together. The letters are seen in "Tainted" line of Oops reports.
See :doc:`/admin-guide/tainted-kernels` for more information.
Note:
writes to this sysctl interface will fail with ``EINVAL`` if the kernel is
booted with the command line option ``panic_on_taint=<bitmask>,nousertaint``
and any of the ORed together values being written to ``tainted`` match with
the bitmask declared on panic_on_taint.
See :doc:`/admin-guide/kernel-parameters` for more details on that particular
kernel command line option and its optional ``nousertaint`` switch.
threads-max
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