linux-kernel - [PATCH v7 6/9] x86/KASLR: Clarify purpose of each get_random

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Message-Id: <1462825332-10505-7-git-send-email-keescook@chromium.org>
Date:	Mon,  9 May 2016 13:22:09 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Kees Cook <keescook@...omium.org>, Borislav Petkov <bp@...e.de>,
	Baoquan He <bhe@...hat.com>, Yinghai Lu <yinghai@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
	Vivek Goyal <vgoyal@...hat.com>,
	Andy Lutomirski <luto@...nel.org>, lasse.collin@...aani.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Young <dyoung@...hat.com>,
	kernel-hardening@...ts.openwall.com,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH v7 6/9] x86/KASLR: Clarify purpose of each get_random_long()

KASLR will be calling get_random_long() twice, but the debug output
won't distinguishing between them. This patch adds a report on when it
is fetching the physical vs virtual address. With this, once the virtual
offset is separate, the report changes from:

KASLR using RDTSC...
KASLR using RDTSC...

into:

Physical KASLR using RDTSC...
Virtual KASLR using RDTSC...

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/x86/boot/compressed/kaslr.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
index 82d00282df3f..c4b1e4b05cb6 100644
--- a/arch/x86/boot/compressed/kaslr.c
+++ b/arch/x86/boot/compressed/kaslr.c
@@ -72,7 +72,7 @@ static unsigned long get_random_boot(void)
 	return hash;
 }
 
-static unsigned long get_random_long(void)
+static unsigned long get_random_long(const char *purpose)
 {
 #ifdef CONFIG_X86_64
 	const unsigned long mix_const = 0x5d6008cbf3848dd3UL;
@@ -82,7 +82,8 @@ static unsigned long get_random_long(void)
 	unsigned long raw, random = get_random_boot();
 	bool use_i8254 = true;
 
-	debug_putstr("KASLR using");
+	debug_putstr(purpose);
+	debug_putstr(" KASLR using");
 
 	if (has_cpuflag(X86_FEATURE_RDRAND)) {
 		debug_putstr(" RDRAND");
@@ -365,7 +366,7 @@ static unsigned long slots_fetch_random(void)
 	if (slot_max == 0)
 		return 0;
 
-	return slots[get_random_long() % slot_max];
+	return slots[get_random_long("Physical") % slot_max];
 }
 
 static void process_e820_entry(struct e820entry *entry,
@@ -453,7 +454,7 @@ static unsigned long find_random_virt_addr(unsigned long minimum,
 	slots = (KERNEL_IMAGE_SIZE - minimum - image_size) /
 		 CONFIG_PHYSICAL_ALIGN + 1;
 
-	random_addr = get_random_long() % slots;
+	random_addr = get_random_long("Virtual") % slots;
 
 	return random_addr * CONFIG_PHYSICAL_ALIGN + minimum;
 }
-- 
2.6.3