On Tue, Mar 31, 2020 at 11:12 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > On Tue, Mar 31, 2020 at 12:41:04AM +0200, Daniel Borkmann wrote: > > On 3/30/20 7:20 PM, Kees Cook wrote: > > > On Mon, Mar 30, 2020 at 06:17:32PM +0200, Jann Horn wrote: > > > > On Mon, Mar 30, 2020 at 5:59 PM Alexei Starovoitov > > > > <alexei.starovoitov@xxxxxxxxx> wrote: > > > > > On Mon, Mar 30, 2020 at 8:14 AM Jann Horn <jannh@xxxxxxxxxx> wrote: > > > > > > > > > > > > I noticed that CONFIG_DEBUG_INFO_BTF seems to partly defeat the point > > > > > > of CONFIG_GCC_PLUGIN_RANDSTRUCT. > > > > > > > > > > Is it a theoretical stmt or you have data? > > > > > I think it's the other way around. > > > > > gcc-plugin breaks dwarf and breaks btf. > > > > > But I only looked at gcc patches without applying them. > > > > > > > > Ah, interesting - I haven't actually tested it, I just assumed > > > > (perhaps incorrectly) that the GCC plugin would deal with DWARF info > > > > properly. > > > > > > Yeah, GCC appears to create DWARF before the plugin does the > > > randomization[1], so it's not an exposure, but yes, struct randomization > > > is pretty completely incompatible with a bunch of things in the kernel > > > (by design). I'm happy to add negative "depends" in the Kconfig if it > > > helps clarify anything. > > > > Is this expected to get fixed at some point wrt DWARF? Perhaps would make > > No, gcc closed the issue as "won't fix". > > > sense then to add a negative "depends" for both DWARF and BTF if the option > > GCC_PLUGIN_RANDSTRUCT is set given both would be incompatible/broken. > > I hadn't just to keep wider randconfig build test coverage. That said, I > could make it be: depends COMPILE_TEST || !DWARF ... > > I can certainly do that. I've asked Slava in [0] to disable all three known configs that break DWARF and subsequently BTF, I hope it's ok to just do it in one patch. Currently all these appear to result in invalid BTF due to various DWARF modifications: - DEBUG_INFO_REDUCED (see [1]) - DEBUG_INFO_SPLIT (see [0] - GCC_PLUGIN_RANDSTRUCT (this discussion). [0] https://lore.kernel.org/bpf/CAEf4BzadnfAwfa1D0jZb=01Ou783GpK_U7PAYeEJca-L9kdnVA@xxxxxxxxxxxxxx/ [1] https://lore.kernel.org/bpf/CAEf4BzZri8KpwLcoPgjiVx_=QmJ2W9UzBkDqSO2rUWMzWogkKg@xxxxxxxxxxxxxx/ > > -Kees > > [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84052 > > -- > Kees Cook
