linux-kernel - [tip:x86/boot] x86/KASLR: Clarify purpose of each get_random

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Message-ID: <tip-d2d3462f9f08da364c8fbd41e8e32229d610d49d@git.kernel.org>
Date:	Tue, 10 May 2016 01:42:48 -0700
From:	tip-bot for Kees Cook <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	dvlasenk@...hat.com, yinghai@...nel.org, akpm@...ux-foundation.org,
	tglx@...utronix.de, peterz@...radead.org, bp@...e.de,
	keescook@...omium.org, torvalds@...ux-foundation.org,
	dyoung@...hat.com, vgoyal@...hat.com, bp@...en8.de, hpa@...or.com,
	luto@...nel.org, mingo@...nel.org, bhe@...hat.com,
	luto@...capital.net, brgerst@...il.com,
	linux-kernel@...r.kernel.org
Subject: [tip:x86/boot] x86/KASLR: Clarify purpose of each get_random_long()

Commit-ID:  d2d3462f9f08da364c8fbd41e8e32229d610d49d
Gitweb:     http://git.kernel.org/tip/d2d3462f9f08da364c8fbd41e8e32229d610d49d
Author:     Kees Cook <keescook@...omium.org>
AuthorDate: Mon, 9 May 2016 13:22:09 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 10 May 2016 10:12:08 +0200

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>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Baoquan He <bhe@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Borislav Petkov <bp@...e.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Dave Young <dyoung@...hat.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Vivek Goyal <vgoyal@...hat.com>
Cc: Yinghai Lu <yinghai@...nel.org>
Cc: kernel-hardening@...ts.openwall.com
Cc: lasse.collin@...aani.org
Link: http://lkml.kernel.org/r/1462825332-10505-7-git-send-email-keescook@chromium.org
Signed-off-by: Ingo Molnar <mingo@...nel.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 016a4f4..cfeb025 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;
 }