The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
Possible dependencies:
d3f450533bbc ("efi: tpm: Avoid READ_ONCE() for accessing the event log") 047d50aee341 ("efi/tpm: Don't access event->count when it isn't mapped") c46f3405692d ("tpm: Reserve the TPM final events table") 44038bc514a2 ("tpm: Abstract crypto agile event size calculations") c8faabfc6f48 ("tpm: add _head suffix to tcg_efi_specid_event and tcg_pcr_event2") 3425d934fc03 ("efi/x86: Handle page faults occurring while running EFI runtime services") 9dbbedaa6171 ("efi: Make efi_rts_work accessible to efi page fault handler") 71e0940d52e1 ("efi: honour memory reservations passed via a linux specific config table")
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From d3f450533bbcb6dd4d7d59cadc9b61b7321e4ac1 Mon Sep 17 00:00:00 2001 From: Ard Biesheuvel ardb@kernel.org Date: Mon, 9 Jan 2023 10:44:31 +0100 Subject: [PATCH] efi: tpm: Avoid READ_ONCE() for accessing the event log
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, but this is already taken care of by the implicit barrier() semantics of the early_memunmap() call.
Cc: stable@vger.kernel.org Cc: Peter Jones pjones@redhat.com Cc: Jarkko Sakkinen jarkko@kernel.org Cc: Matthew Garrett mjg59@srcf.ucam.org Reported-by: Nathan Chancellor nathan@kernel.org Tested-by: Nathan Chancellor nathan@kernel.org Link: https://github.com/ClangBuiltLinux/linux/issues/1782 Signed-off-by: Ard Biesheuvel ardb@kernel.org
diff --git a/include/linux/tpm_eventlog.h b/include/linux/tpm_eventlog.h index 20c0ff54b7a0..7d68a5cc5881 100644 --- a/include/linux/tpm_eventlog.h +++ b/include/linux/tpm_eventlog.h @@ -198,8 +198,8 @@ static __always_inline int __calc_tpm2_event_size(struct tcg_pcr_event2_head *ev * The loop below will unmap these fields if the log is larger than * one page, so save them here for reference: */ - count = READ_ONCE(event->count); - event_type = READ_ONCE(event->event_type); + count = event->count; + event_type = event->event_type;
/* Verify that it's the log header */ if (event_header->pcr_idx != 0 ||