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

From: Kees Cook
Date: Wed Apr 20 2016 - 16:56:07 EST


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@xxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
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