Messages in this thread Patch in this message | | | Date | Mon, 10 Aug 2020 17:06:50 +0200 | From | Jessica Yu <> | Subject | Re: [PATCH v2] module: Harden STRICT_MODULE_RWX |
| |
+++ Jessica Yu [10/08/20 11:25 +0200]: >+++ Mauro Carvalho Chehab [08/08/20 10:12 +0200]: >[snip] >>Right now, what happens is: >> >> # modprobe wlcore >> modprobe: ERROR: could not insert 'wlcore': Exec format error >> >>This seems to be failing for all modules, as doesn't show anything >>probed. >> >>Btw, IMO, it would be useful to have some pr_debug() infra in order to >>explain why insmod is failing, or to have more error codes used there, >>as nothing was printed at dmesg. That makes harder to debug issues >>there. I ended losing a lot of time yesterday rebuilding the Kernel >>and checking the FS, before deciding to add some printks inside the >>Kernel ;-) >> >>In order for modprobe to start working again, I had to apply this >>dirty hack: >> >><hack> >>diff --git a/kernel/module.c b/kernel/module.c >>index 910a57640818..10d590dc48ad 100644 >>--- a/kernel/module.c >>+++ b/kernel/module.c >>@@ -2051,11 +2051,12 @@ static int module_enforce_rwx_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs, >> const unsigned long shf_wx = SHF_WRITE|SHF_EXECINSTR; >> int i; >> >>+#if 0 >> for (i = 0; i < hdr->e_shnum; i++) { >> if ((sechdrs[i].sh_flags & shf_wx) == shf_wx) >> return -ENOEXEC; >> } >>- >>+#endif >> return 0; >>} >></hack>
[ I somehow munged the To: header in the last mail. Sorry about that, it's fixed now. ]
>All this hunk does it reject loading modules that have any sections >that have both the writable and executable flags. You're saying it's >happening for all modules on your setup - I am curious as to which >sections have both these flags - what does readelf -S tell you?
Hmm, I was not able to reproduce this with a cross-compiled kernel using the attached config (gcc 9.3.0 with vanilla v5.8 kernel). I am curious if the failing sections are also SHF_ALLOC - in that case, the code is doing what it is intended to do, which is rejecting loading any modules with writable and executable sections. If the problematic sections are *not* SHF_ALLOC, then we might be able to work around that by ignoring non-SHF_ALLOC sections as they are not copied to the final module location anyway.
Jessica
| |