Messages in this thread | | | Date | Mon, 6 Apr 2020 14:53:37 +0200 | From | Jessica Yu <> | Subject | Re: [PATCH] module: Harden STRICT_MODULE_RWX |
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+++ Peter Zijlstra [06/04/20 13:27 +0200]: >On Mon, Apr 06, 2020 at 12:46:17PM +0200, Jessica Yu wrote: >> +++ Miroslav Benes [06/04/20 11:55 +0200]: >> > On Fri, 3 Apr 2020, Josh Poimboeuf wrote: >> > >> > > On Fri, Apr 03, 2020 at 06:37:16PM +0200, Peter Zijlstra wrote: >> > > > +{ >> > > > + int i; >> > > > + >> > > > + for (i = 0; i < hdr->e_shnum; i++) { >> > > > + if (sechdrs[i].sh_flags & (SHF_EXECINSTR|SHF_WRITE)) >> > > > + return -ENOEXEC; >> > > >> > > I think you only want the error when both are set? >> > > >> > > if (sechdrs[i].sh_flags & (SHF_EXECINSTR|SHF_WRITE) == (SHF_EXECINSTR|SHF_WRITE)) >> > >> > A section with SHF_EXECINSTR and SHF_WRITE but without SHF_ALLOC would be >> > strange though, no? It wouldn't be copied to the final module later >> > anyway. >> >> That's right - move_module() ignores !SHF_ALLOC sections and does not >> copy them over to their final location. So I think we want to look for >> SHF_EXECINSTR|SHF_WRITE|SHF_ALLOC here.. > >So I did notice that !SHF_ALLOC sections get ignored, but since this >check is about W^X we don't strictly care about SHF_ALLOC. What we care >about it never allowing a writable and executable map. > >Adding ALLOC to the test only allows for future mistakes and doesn't >make the check any better.
Ugh sorry, my brain shorted out and for some reason I mistakenly thought the check excluded SHF_WRITE|SHF_EXECINSTR|SHF_ALLOC sections. It doesn't obviously. Sorry for the noise.
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