Re: taint/module: Clean up global and module taint flags handling

From: Jessica Yu
Date: Fri Sep 23 2016 - 00:48:47 EST

+++ Petr Mladek [21/09/16 13:47 +0200]:
The commit 66cc69e34e86a231 ("Fix: module signature vs tracepoints:
add new TAINT_UNSIGNED_MODULE") updated module_taint_flags() to
potentially print one more character. But it did not increase the
size of the corresponding buffers in m_show() and print_modules().

We have recently done the same mistake when adding a taint flag
for livepatching, see

Also struct module uses an incompatible type for mod-taints flags.
It survived from the commit 2bc2d61a9638dab670d ("[PATCH] list module
taint flags in Oops/panic"). There was used "int" for the global taint
flags at these times. But only the global tain flags was later changed
to "unsigned long" by the commit 25ddbb18aae33ad2 ("Make the taint
flags reliable").

This patch defines TAINT_FLAGS_COUNT that can be used to create
arrays and buffers of the right size. Note that we could not use
enum because the taint flag indexes are used also in assembly code.

Then it reworks the table that describes the taint flags. The TAINT_*
numbers can be used as the index. Instead, we add information
if the taint flag is also shown per-module.

Finally, it uses "unsigned long", bit operations, and the updated
taint_flags table also for mod->taints.

It is not optimal because only few taint flags can be printed by
module_taint_flags(). But better be on the safe side. IMHO, it is
not worth the optimization and this is a good compromise.

Signed-off-by: Petr Mladek <pmladek@xxxxxxxx>
Changes against v2:

+ fixed a typo in a comment

+ rebased on top of for-next branch from git/jikos/livepatching.git
that has the commit commit 2992ef29ae01af9983 ("livepatch/module:
make TAINT_LIVEPATCH module-specific").

Reviewed-by: Jessica Yu <jeyu@xxxxxxxxxx>

Hm, quick question, which tree would this patch go to? Though the
cleanup is for modules, there is an indirect cross-tree dependency
(taint_flag.module needs to be true for TAINT_LIVEPATCH for Josh's
patch to still work as intended). The least complicated thing to do
would be to just take this through the livepatch tree (with Rusty's
approval :-)), no?