efi/bgrt: Skip efi_bgrt_init() in case of non-EFI boot

Sabrina Dubroca reported an early panic:

  BUG: unable to handle kernel paging request at ffffffffff240001
  IP: efi_bgrt_init+0xdc/0x134

  [...]

  ---[ end Kernel panic - not syncing: Attempted to kill the idle task!

... which was introduced by:

  7b0a911478c7 ("efi/x86: Move the EFI BGRT init code to early init code")

The cause is that on this machine the firmware provides the EFI ACPI BGRT
table even on legacy non-EFI bootups - which table should be EFI only.

The garbage BGRT data causes the efi_bgrt_init() panic.

Add a check to skip efi_bgrt_init() in case non-EFI bootup to work around
this firmware bug.

Tested-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: Dave Young <dyoung@redhat.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Cc: <stable@vger.kernel.org> # v4.11+
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Fixes: 7b0a911478c7 ("efi/x86: Move the EFI BGRT init code to early init code")
Link: http://lkml.kernel.org/r/20170526113652.21339-6-matt@codeblueprint.co.uk
[ Rewrote the changelog to be more readable. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/firmware/efi/efi-bgrt.c b/drivers/firmware/efi/efi-bgrt.c
index 04ca8764f0c0..8bf27323f7a3 100644
--- a/drivers/firmware/efi/efi-bgrt.c
+++ b/drivers/firmware/efi/efi-bgrt.c
@@ -36,6 +36,9 @@ void __init efi_bgrt_init(struct acpi_table_header *table)
         if (acpi_disabled)
                 return;
 
+        if (!efi_enabled(EFI_BOOT))
+                return;
+
         if (table->length < sizeof(bgrt_tab)) {
                 pr_notice("Ignoring BGRT: invalid length %u (expected %zu)\n",
                        table->length, sizeof(bgrt_tab));