Messages in this thread | | | Date | Tue, 1 Sep 2020 13:51:15 +0100 | From | Will Deacon <> | Subject | Re: [PATCH v2] module: Harden STRICT_MODULE_RWX |
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On Mon, Aug 31, 2020 at 11:46:51AM +0200, Jessica Yu wrote: > +++ Will Deacon [21/08/20 13:30 +0100]: > [snipped] > > > > > > 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. > > > > Ok, if it's _not_ straightforward, then let's just drop the IS_ENABLED() > > altogether. > > Unfortunately I've been getting more reports about this issue, so let's just > get the aforementioned workaround merged first. Does the following look OK? > > diff --git a/arch/arm64/kernel/module-plts.c b/arch/arm64/kernel/module-plts.c > index 0ce3a28e3347..2e224435c024 100644 > --- a/arch/arm64/kernel/module-plts.c > +++ b/arch/arm64/kernel/module-plts.c > @@ -305,8 +305,7 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, > mod->arch.core.plt_shndx = i; > else if (!strcmp(secstrings + sechdrs[i].sh_name, ".init.plt")) > mod->arch.init.plt_shndx = i; > - else if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE) && > - !strcmp(secstrings + sechdrs[i].sh_name, > + else if (!strcmp(secstrings + sechdrs[i].sh_name, > ".text.ftrace_trampoline")) > tramp = sechdrs + i; > else if (sechdrs[i].sh_type == SHT_SYMTAB) > > If so I'll turn it into a formal patch and we can get that merged in the next -rc.
Acked-by: Will Deacon <will@kernel.org>
Will
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