On Mon, 9 Jan 2023 at 18:48, Nathan Chancellor <nathan@xxxxxxxxxx> wrote: > > On Mon, Jan 09, 2023 at 10:59:48AM +0100, Ard Biesheuvel wrote: > > Nathan reports that recent kernels built with LTO will crash when doing > > EFI boot using Fedora's GRUB and SHIM. The culprit turns out to be a > > misaligned load from the TPM event log, which is annotated with > > READ_ONCE(), and under LTO, this gets translated into a LDAR instruction > > which does not tolerate misaligned accesses. > > > > Interestingly, this does not happen when booting the same kernel > > straight from the UEFI shell, and so the fact that the event log may > > appear misaligned in memory may be caused by a bug in GRUB or SHIM. > > > > However, using READ_ONCE() to access firmware tables is slightly unusual > > in any case, and here, we only need to ensure that 'event' is not > > dereferenced again after it gets unmapped, so a compiler barrier should > > be sufficient, and works around the reported issue. > > > > Cc: <stable@xxxxxxxxxxxxxxx> > > Cc: Peter Jones <pjones@xxxxxxxxxx> > > Cc: Jarkko Sakkinen <jarkko@xxxxxxxxxx> > > Cc: Matthew Garrett <mjg59@xxxxxxxxxxxxx> > > Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx> > > Link: https://github.com/ClangBuiltLinux/linux/issues/1782 > > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > > Based on the thread, I tested this patch without barrier() and my > machine boots up just fine now with an LTO kernel. Thanks a lot for the > analysis and fix! > > Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx> > Thanks. I've queued this up as a EFI fix.
