On Fri, 21 Aug 2020 at 14:20, Will Deacon <w...@kernel.org> wrote: > > On Thu, Aug 13, 2020 at 03:07:13PM +0200, Ard Biesheuvel wrote: > > On Thu, 13 Aug 2020 at 15:04, Jessica Yu <j...@kernel.org> wrote: > > > > > > +++ Ard Biesheuvel [13/08/20 10:36 +0200]: > > > >On Wed, 12 Aug 2020 at 22:00, Peter Zijlstra <pet...@infradead.org> > > > >wrote: > > > >> > > > >> On Wed, Aug 12, 2020 at 06:37:57PM +0200, Ard Biesheuvel wrote: > > > >> > I know there is little we can do at this point, apart from ignoring > > > >> > the permissions - perhaps we should just defer the w^x check until > > > >> > after calling module_frob_arch_sections()? > > > >> > > > >> My earlier suggestion was to ignore it for 0-sized sections. > > > > > > > >Only they are 1 byte sections in this case. > > > > > > > >We override the sh_type and sh_flags explicitly for these sections at > > > >module load time, so deferring the check seems like a reasonable > > > >alternative to me. > > > > > > So module_enforce_rwx_sections() is already called after > > > module_frob_arch_sections() - which really baffled me at first, since > > > sh_type and sh_flags should have been set already in > > > module_frob_arch_sections(). > > > > > > I added some debug prints to see which section the module code was > > > tripping on, and it was .text.ftrace_trampoline. See this snippet from > > > arm64's module_frob_arch_sections(): > > > > > > else if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) && > > > !strcmp(secstrings + sechdrs[i].sh_name, > > > ".text.ftrace_trampoline")) > > > tramp = sechdrs + i; > > > > > > Since Mauro's config doesn't have CONFIG_DYNAMIC_FTRACE enabled, tramp > > > is never set here and the if (tramp) check at the end of the function > > > fails, so its section flags are never set, so they remain WAX and fail > > > the rwx check. > > > > Right. Our module.lds does not go through the preprocessor, so we > > cannot add the #ifdef check there currently. So we should either drop > > the IS_ENABLED() check here, or simply rename the section, dropping > > the .text prefix (which doesn't seem to have any significance outside > > this context) > > > > I'll leave it to Will to make the final call here. > > Why don't we just preprocess the linker script, like we do for the main > kernel? >
That should work as well, I just haven't checked how straight-forward it is to change that.
