From: Hans de Goede <hdegoede@redhat.com>
Date: Tue, 24 Dec 2019 14:29:08 +0100
Subject: efi/libstub/random: Initialize pointer variables to zero for mixed
 mode
Patch-mainline: v5.5-rc7
Git-commit: 818c7ce724770fbcdcd43725c81f2b3535f82b76
References: jsc#SLE-16407

Commit:

  0d95981438c3 ("x86: efi/random: Invoke EFI_RNG_PROTOCOL to seed the UEFI RNG table")

causes the drivers/efi/libstub/random.c code to get used on x86 for the first time.

But this code was not written with EFI mixed mode in mind (running a 64
bit kernel on 32 bit EFI firmware), this causes the kernel to crash during
early boot when running in mixed mode.

The problem is that in mixed mode pointers are 64 bit, but when running on
a 32 bit firmware, EFI calls which return a pointer value by reference only
fill the lower 32 bits of the passed pointer, leaving the upper 32 bits
uninitialized which leads to crashes.

This commit fixes this by initializing pointers which are passed by
reference to EFI calls to NULL before passing them, so that the upper 32
bits are initialized to 0.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Cc: Arvind Sankar <nivedita@alum.mit.edu>
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: 0d95981438c3 ("x86: efi/random: Invoke EFI_RNG_PROTOCOL to seed the UEFI RNG table")
Link: https://lkml.kernel.org/r/20191224132909.102540-3-ardb@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Lee, Chun-Yi <jlee@suse.com>
---
 drivers/firmware/efi/libstub/random.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/firmware/efi/libstub/random.c
+++ b/drivers/firmware/efi/libstub/random.c
@@ -33,7 +33,7 @@ efi_status_t efi_get_random_bytes(efi_sy
 {
 	efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
 	efi_status_t status;
-	struct efi_rng_protocol *rng;
+	struct efi_rng_protocol *rng = NULL;
 
 	status = efi_call_early(locate_protocol, &rng_proto, NULL,
 				(void **)&rng);
@@ -158,8 +158,8 @@ efi_status_t efi_random_get_seed(efi_sys
 	efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
 	efi_guid_t rng_algo_raw = EFI_RNG_ALGORITHM_RAW;
 	efi_guid_t rng_table_guid = LINUX_EFI_RANDOM_SEED_TABLE_GUID;
-	struct efi_rng_protocol *rng;
-	struct linux_efi_random_seed *seed;
+	struct efi_rng_protocol *rng = NULL;
+	struct linux_efi_random_seed *seed = NULL;
 	efi_status_t status;
 
 	status = efi_call_early(locate_protocol, &rng_proto, NULL,