Messages in this thread | | | Date | Mon, 15 Jun 2020 11:47:21 -0700 | From | Kees Cook <> | Subject | Re: [PATCH] security: fix the key_permission LSM hook function type |
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On Mon, Jun 15, 2020 at 11:23:44AM -0700, Nick Desaulniers wrote: > On Mon, Jun 15, 2020 at 11:21 AM Kees Cook <keescook@chromium.org> wrote: > > > > On Mon, Jun 15, 2020 at 11:12:32AM -0700, Sami Tolvanen wrote: > > > Commit 8c0637e950d6 ("keys: Make the KEY_NEED_* perms an enum rather than > > > a mask") changed the type of the key_permission callback functions, but > > > didn't change the type of the hook, which trips indirect call checking with > > > Control-Flow Integrity (CFI). This change fixes the issue by changing the > > > hook type to match the functions. > > > > > > Fixes: 8c0637e950d6 ("keys: Make the KEY_NEED_* perms an enum rather than a mask") > > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > > > > Thanks for fixing this! > > > > Acked-by: Kees Cook <keescook@chromium.org> > > > > I wonder if there is any compiler option we can turn on to catch the > > implicit enum/int casting that would help for these kinds of things > > without absolutely exploding the build warnings. > > > > I see -Wenum-conversion, but that seems to be between enums, not between > > int. > > > > I see this, but it's external: > > https://noamlewis.wordpress.com/2017/10/05/type-safe-enums-in-c-using-a-clang-plugin/ > > Unfortunately, using a looser integral type is the typical workaround > for -Wenum-conversion warnings (which is on by default, GCC recently > added that flag, too). For warning on enum to int, the kernel would > probably blow up with warnings. I don't know of any such existing > warning flag.
Yeah, I couldn't find anything either. The closest I could find to avoid one of the common classes of enum -> int conversion is the bitwise operations, which is covered by __attribute__((flag_enum)): https://clang.llvm.org/docs/AttributeReference.html#flag-enum
Ah well. We'll let CFI find them. ;)
-- Kees Cook
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