[tip:efi/urgent] efi/bgrt: Skip efi_bgrt_init() in case of non-EFI boot

[tip-bot for Dave Young <tipbot@zytor.com>]

Commit-ID:  7425826f4f7ac60f2538b06a7f0a5d1006405159
Gitweb:     http://git.kernel.org/tip/7425826f4f7ac60f2538b06a7f0a5d1006405159
Author:     Dave Young <dyoung@redhat.com>
AuthorDate: Fri, 26 May 2017 12:36:51 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Sun, 28 May 2017 11:06:17 +0200

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>
---
 drivers/firmware/efi/efi-bgrt.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/firmware/efi/efi-bgrt.c b/drivers/firmware/efi/efi-bgrt.c
index 04ca876..8bf2732 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));