linux-kernel - [PATCH v3 2/7] x86: Use simpler API for random address requests

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Date:	Wed,  3 Aug 2016 23:39:08 +0000
From:	Jason Cooper <jason@...edaemon.net>
To:	Kees Cook <keescook@...omium.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	"Roberts, William C" <william.c.roberts@...el.com>,
	Yann Droneaud <ydroneaud@...eya.com>
Cc:	"Linux-MM" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"kernel-hardening" <kernel-hardening@...ts.openwall.com>,
	"Russell King - ARM Linux" <linux@....linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Theodore Ts'o" <tytso@....edu>, Arnd Bergmann <arnd@...db.de>,
	gregkh@...uxfoundation.org,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Ralf Baechle <ralf@...ux-mips.org>, benh@...nel.crashing.org,
	paulus@...ba.org, "David S. Miller" <davem@...emloft.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	viro@...iv.linux.org.uk, Nick Kralevich <nnk@...gle.com>,
	Jeffrey Vander Stoep <jeffv@...gle.com>,
	Daniel Cashman <dcashman@...roid.com>,
	Jason Cooper <jason@...edaemon.net>
Subject: [PATCH v3 2/7] x86: Use simpler API for random address requests

Currently, all callers to randomize_range() set the length to 0 and
calculate end by adding a constant to the start address.  We can
simplify the API to remove a bunch of needless checks and variables.

Use the new randomize_addr(start, range) call to set the requested
address.

Signed-off-by: Jason Cooper <jason@...edaemon.net>
---
Changes from v2:
 - s/randomize_addr/randomize_page/ (Kees Cook)

 arch/x86/kernel/process.c    | 3 +--
 arch/x86/kernel/sys_x86_64.c | 5 +----
 2 files changed, 2 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 96becbbb52e0..8ca7f42d97f3 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -507,8 +507,7 @@ unsigned long arch_align_stack(unsigned long sp)
 
 unsigned long arch_randomize_brk(struct mm_struct *mm)
 {
-	unsigned long range_end = mm->brk + 0x02000000;
-	return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
+	return randomize_page(mm->brk, 0x02000000);
 }
 
 /*
diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
index 10e0272d789a..a55ed63b9f91 100644
--- a/arch/x86/kernel/sys_x86_64.c
+++ b/arch/x86/kernel/sys_x86_64.c
@@ -101,7 +101,6 @@ static void find_start_end(unsigned long flags, unsigned long *begin,
 			   unsigned long *end)
 {
 	if (!test_thread_flag(TIF_ADDR32) && (flags & MAP_32BIT)) {
-		unsigned long new_begin;
 		/* This is usually used needed to map code in small
 		   model, so it needs to be in the first 31bit. Limit
 		   it to that.  This means we need to move the
@@ -112,9 +111,7 @@ static void find_start_end(unsigned long flags, unsigned long *begin,
 		*begin = 0x40000000;
 		*end = 0x80000000;
 		if (current->flags & PF_RANDOMIZE) {
-			new_begin = randomize_range(*begin, *begin + 0x02000000, 0);
-			if (new_begin)
-				*begin = new_begin;
+			*begin = randomize_page(*begin, 0x02000000);
 		}
 	} else {
 		*begin = current->mm->mmap_legacy_base;
-- 
2.9.2