From 9115c7589b11349a1c3099758b4bded579ff69e0 Mon Sep 17 00:00:00 2001
From: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Date: Wed, 15 Jul 2015 19:36:03 -0700
Subject: [PATCH] efi: Check for NULL efi kernel parameters

Even though it is documented how to specifiy efi parameters, it is
possible to cause a kernel panic due to a dereference of a NULL pointer when
parsing such parameters if "efi" alone is given:

PANIC: early exception 0e rip 10:ffffffff812fb361 error 0 cr2 0
[ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.2.0-rc1+ #450
[ 0.000000]  ffffffff81fe20a9 ffffffff81e03d50 ffffffff8184bb0f 00000000000003f8
[ 0.000000]  0000000000000000 ffffffff81e03e08 ffffffff81f371a1 64656c62616e6520
[ 0.000000]  0000000000000069 000000000000005f 0000000000000000 0000000000000000
[ 0.000000] Call Trace:
[ 0.000000]  [<ffffffff8184bb0f>] dump_stack+0x45/0x57
[ 0.000000]  [<ffffffff81f371a1>] early_idt_handler_common+0x81/0xae
[ 0.000000]  [<ffffffff812fb361>] ? parse_option_str+0x11/0x90
[ 0.000000]  [<ffffffff81f4dd69>] arch_parse_efi_cmdline+0x15/0x42
[ 0.000000]  [<ffffffff81f376e1>] do_early_param+0x50/0x8a
[ 0.000000]  [<ffffffff8106b1b3>] parse_args+0x1e3/0x400
[ 0.000000]  [<ffffffff81f37a43>] parse_early_options+0x24/0x28
[ 0.000000]  [<ffffffff81f37691>] ? loglevel+0x31/0x31
[ 0.000000]  [<ffffffff81f37a78>] parse_early_param+0x31/0x3d
[ 0.000000]  [<ffffffff81f3ae98>] setup_arch+0x2de/0xc08
[ 0.000000]  [<ffffffff8109629a>] ? vprintk_default+0x1a/0x20
[ 0.000000]  [<ffffffff81f37b20>] start_kernel+0x90/0x423
[ 0.000000]  [<ffffffff81f37495>] x86_64_start_reservations+0x2a/0x2c
[ 0.000000]  [<ffffffff81f37582>] x86_64_start_kernel+0xeb/0xef
[ 0.000000] RIP 0xffffffff81ba2efc

This panic is not reproducible with "efi=" as this will result in a non-NULL
zero-length string.

Thus, verify that the pointer to the parameter string is not NULL. This is
consistent with other parameter-parsing functions which check for NULL pointers.

Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
---
 arch/x86/platform/efi/efi.c | 5 +++++
 drivers/firmware/efi/efi.c  | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index cfba30f27392..e4308fe6afe8 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -972,6 +972,11 @@ u64 efi_mem_attributes(unsigned long phys_addr)
 
 static int __init arch_parse_efi_cmdline(char *str)
 {
+	if (!str) {
+		pr_warn("need at least one option\n");
+		return -EINVAL;
+	}
+
 	if (parse_option_str(str, "old_map"))
 		set_bit(EFI_OLD_MEMMAP, &efi.flags);
 	if (parse_option_str(str, "debug"))
diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 9fa8084a7c8d..d6144e3b97c5 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -58,6 +58,11 @@ bool efi_runtime_disabled(void)
 
 static int __init parse_efi_cmdline(char *str)
 {
+	if (!str) {
+		pr_warn("need at least one option\n");
+		return -EINVAL;
+	}
+
 	if (parse_option_str(str, "noruntime"))
 		disable_runtime = true;