On Mon, 30 May 2022, Jani Nikula <jani.nikula@xxxxxxxxx> wrote: > On Sat, 28 May 2022, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: >> On Sat, May 28, 2022 at 11:59 AM Arnd Bergmann <arnd@xxxxxxxx> wrote: >>> >>> It's CONFIG_ARM_AEABI, which is normally set everywhere. Without this >>> option, you the kernel is built for the old 'OABI' that forces all non-packed >>> struct members to be at least 16-bit aligned. >> >> Looks like forced word (32 bit) alignment to me. >> >> I wonder how many other structures that messes up, but I committed the >> EDID fix for now. > > Thanks for the fix, and the thorough commit message! > >> This has presumably been broken for a long time, but maybe the >> affected targets don't typically use EDID and kernel modesetting, and >> only use some fixed display setup instead. >> >> Those structure definitions go back a _loong_ time (from a quick 'git >> blame' I see November 2008). >> >> But despite that, I did not mark my fix 'cc:stable' because I don't >> know if any of those machines affected by this bad arm ABI issue could >> possibly care. >> >> At least my tree hopefully now builds on them, with the BUILD_BUG_ON() >> that uncovered this. > > Indeed the bug is ancient. I just threw in the BUILD_BUG_ON() on a whim > as an extra sanity check when doing pointer arithmetics on struct edid > *. > > If there are affected machines, buffer overflows are the real danger due > to edid->extensions indicating the number of extensions. That is, for EDID. Makes you wonder about all the other packed structs with enum members across the kernel. BR, Jani. -- Jani Nikula, Intel Open Source Graphics Center
