linux-kernel - [PATCH] x86/ima: use correct identifier for SetupMode variable

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Message-Id: <20200201083221.20193-1-ardb@kernel.org>
Date:   Sat,  1 Feb 2020 09:32:21 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
        Matthew Garrett <mjg59@...gle.com>,
        Mimi Zohar <zohar@...ux.ibm.com>
Subject: [PATCH] x86/ima: use correct identifier for SetupMode variable

The IMA arch code attempts to inspect the "SetupMode" EFI variable
by populating a variable called efi_SetupMode_name with the string
"SecureBoot" and passing that to the EFI GetVariable service, which
obviously does not yield the expected result.

Given that the string is only referenced a single time, let's get
rid of the intermediate variable, and pass the correct string as
an immediate argument. While at it, do the same for "SecureBoot".

Fixes: 399574c64eaf ("x86/ima: retry detecting secure boot mode")
Fixes: 980ef4d22a95 ("x86/ima: check EFI SetupMode too")
Cc: Matthew Garrett <mjg59@...gle.com>
Cc: Mimi Zohar <zohar@...ux.ibm.com>
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---

The bug results in get_sb_mode() to always return efi_secureboot_mode_disabled.

I am not too familiar with this code, but it seems get_sb_mode() is only
called when the secure boot state has not been established yet, but I don't
know how likely that is to occur in practice.

 arch/x86/kernel/ima_arch.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/ima_arch.c b/arch/x86/kernel/ima_arch.c
index 4d4f5d9faac3..23054909c8dd 100644
--- a/arch/x86/kernel/ima_arch.c
+++ b/arch/x86/kernel/ima_arch.c
@@ -10,8 +10,6 @@ extern struct boot_params boot_params;
 
 static enum efi_secureboot_mode get_sb_mode(void)
 {
-	efi_char16_t efi_SecureBoot_name[] = L"SecureBoot";
-	efi_char16_t efi_SetupMode_name[] = L"SecureBoot";
 	efi_guid_t efi_variable_guid = EFI_GLOBAL_VARIABLE_GUID;
 	efi_status_t status;
 	unsigned long size;
@@ -25,7 +23,7 @@ static enum efi_secureboot_mode get_sb_mode(void)
 	}
 
 	/* Get variable contents into buffer */
-	status = efi.get_variable(efi_SecureBoot_name, &efi_variable_guid,
+	status = efi.get_variable(L"SecureBoot", &efi_variable_guid,
 				  NULL, &size, &secboot);
 	if (status == EFI_NOT_FOUND) {
 		pr_info("ima: secureboot mode disabled\n");
@@ -38,7 +36,7 @@ static enum efi_secureboot_mode get_sb_mode(void)
 	}
 
 	size = sizeof(setupmode);
-	status = efi.get_variable(efi_SetupMode_name, &efi_variable_guid,
+	status = efi.get_variable(L"SetupMode", &efi_variable_guid,
 				  NULL, &size, &setupmode);
 
 	if (status != EFI_SUCCESS)	/* ignore unknown SetupMode */
-- 
2.17.1