linux-kernel - [PATCH 5/5] x86, KASLR: Warn when KASLR is disabled

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Date:	Wed, 20 Apr 2016 13:55:46 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Kees Cook <keescook@...omium.org>, Yinghai Lu <yinghai@...nel.org>,
	Baoquan He <bhe@...hat.com>, Ingo Molnar <mingo@...hat.com>,
	x86@...nel.org, Andrew Morton <akpm@...ux-foundation.org>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	"H.J. Lu" <hjl.tools@...il.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Borislav Petkov <bp@...e.de>,
	Andy Lutomirski <luto@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH 5/5] x86, KASLR: Warn when KASLR is disabled

If KASLR is built in but not available at run-time (either due to the
current conflict with hibernation, command-line request, or e820 parsing
failures), announce the state explicitly. To support this, a new "warn"
function is created, based on the existing "error" function.

Suggested-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/x86/boot/compressed/kaslr.c |  6 +++---
 arch/x86/boot/compressed/misc.c  | 12 +++++++++---
 arch/x86/boot/compressed/misc.h  |  1 +
 3 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 3ad71a0afa24..8741a6d83bfe 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -314,12 +314,12 @@ unsigned char *choose_random_location(unsigned char *input,
 
 #ifdef CONFIG_HIBERNATION
 	if (!cmdline_find_option_bool("kaslr")) {
-		debug_putstr("KASLR disabled by default...\n");
+		warn("KASLR disabled: 'kaslr' not on cmdline (hibernation selected).");
 		goto out;
 	}
 #else
 	if (cmdline_find_option_bool("nokaslr")) {
-		debug_putstr("KASLR disabled by cmdline...\n");
+		warn("KASLR disabled: 'nokaslr' on cmdline.");
 		goto out;
 	}
 #endif
@@ -333,7 +333,7 @@ unsigned char *choose_random_location(unsigned char *input,
 	/* Walk e820 and find a random address. */
 	random_addr = find_random_addr(choice, output_size);
 	if (!random_addr) {
-		debug_putstr("KASLR could not find suitable E820 region...\n");
+		warn("KASLR disabled: could not find suitable E820 region!");
 		goto out;
 	}
 
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index eacc855ae08e..c57d785ff955 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -166,11 +166,17 @@ void __puthex(unsigned long value)
 	}
 }
 
-static void error(char *x)
+void warn(char *m)
 {
 	error_putstr("\n\n");
-	error_putstr(x);
-	error_putstr("\n\n -- System halted");
+	error_putstr(m);
+	error_putstr("\n\n");
+}
+
+static void error(char *m)
+{
+	warn(m);
+	error_putstr(" -- System halted");
 
 	while (1)
 		asm("hlt");
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index 9887e0d4aaeb..e75f6cf9caaf 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -35,6 +35,7 @@ extern memptr free_mem_end_ptr;
 extern struct boot_params *boot_params;
 void __putstr(const char *s);
 void __puthex(unsigned long value);
+void warn(char *m);
 #define error_putstr(__x)  __putstr(__x)
 #define error_puthex(__x)  __puthex(__x)
 
-- 
2.6.3