linux-kernel - [PATCH v4 03/10] arm64: standardize mmap

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Date:	Wed,  4 Mar 2015 13:10:47 -0800
From:	Kees Cook <keescook@...omium.org>
To:	akpm@...ux-foundation.org
Cc:	Kees Cook <keescook@...omium.org>, Ingo Molnar <mingo@...hat.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Hector Marco-Gisbert <hecmargi@....es>,
	Ismael Ripoll <iripoll@....es>,
	Russell King <linux@....linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux390@...ibm.com, x86@...nel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andy Lutomirski <luto@...capital.net>,
	Oleg Nesterov <oleg@...hat.com>,
	"David A. Long" <dave.long@...aro.org>,
	Andrey Ryabinin <a.ryabinin@...sung.com>,
	Arun Chandran <achandran@...sta.com>,
	Yann Droneaud <ydroneaud@...eya.com>,
	Min-Hua Chen <orca.chen@...il.com>,
	Paul Burton <paul.burton@...tec.com>,
	Alex Smith <alex@...x-smith.me.uk>,
	Markos Chandras <markos.chandras@...tec.com>,
	Vineeth Vijayan <vvijayan@...sta.com>,
	Jeff Bailey <jeffbailey@...gle.com>,
	Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	Borislav Petkov <bp@...e.de>,
	Jan-Simon Möller <dl9pf@....de>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-mips@...ux-mips.org, linuxppc-dev@...ts.ozlabs.org,
	linux-s390@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: [PATCH v4 03/10] arm64: standardize mmap_rnd() usage

In preparation for splitting out ET_DYN ASLR, this refactors the use of
mmap_rnd() to be used similarly to arm and x86. This additionally enables
mmap ASLR on legacy mmap layouts, which appeared to be missing on arm64,
and was already supported on arm. Additionally removes a copy/pasted
declaration of an unused function.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/arm64/include/asm/elf.h |  1 -
 arch/arm64/mm/mmap.c         | 18 +++++++++++-------
 2 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 1f65be393139..f724db00b235 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -125,7 +125,6 @@ typedef struct user_fpsimd_state elf_fpregset_t;
  * the loader.  We need to make sure that it is out of the way of the program
  * that it will "exec", and that there is sufficient room for the brk.
  */
-extern unsigned long randomize_et_dyn(unsigned long base);
 #define ELF_ET_DYN_BASE	(2 * TASK_SIZE_64 / 3)
 
 /*
diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index 54922d1275b8..ba776c01b552 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -49,15 +49,14 @@ static int mmap_is_legacy(void)
 
 static unsigned long mmap_rnd(void)
 {
-	unsigned long rnd = 0;
+	unsigned long rnd;
 
-	if (current->flags & PF_RANDOMIZE)
-		rnd = (long)get_random_int() & STACK_RND_MASK;
+	rnd = (unsigned long)get_random_int() & STACK_RND_MASK;
 
 	return rnd << PAGE_SHIFT;
 }
 
-static unsigned long mmap_base(void)
+static unsigned long mmap_base(unsigned long rnd)
 {
 	unsigned long gap = rlimit(RLIMIT_STACK);
 
@@ -66,7 +65,7 @@ static unsigned long mmap_base(void)
 	else if (gap > MAX_GAP)
 		gap = MAX_GAP;
 
-	return PAGE_ALIGN(STACK_TOP - gap - mmap_rnd());
+	return PAGE_ALIGN(STACK_TOP - gap - rnd);
 }
 
 /*
@@ -75,15 +74,20 @@ static unsigned long mmap_base(void)
  */
 void arch_pick_mmap_layout(struct mm_struct *mm)
 {
+	unsigned long random_factor = 0UL;
+
+	if (current->flags & PF_RANDOMIZE)
+		random_factor = mmap_rnd();
+
 	/*
 	 * Fall back to the standard layout if the personality bit is set, or
 	 * if the expected stack growth is unlimited:
 	 */
 	if (mmap_is_legacy()) {
-		mm->mmap_base = TASK_UNMAPPED_BASE;
+		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
 		mm->get_unmapped_area = arch_get_unmapped_area;
 	} else {
-		mm->mmap_base = mmap_base();
+		mm->mmap_base = mmap_base(random_factor);
 		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 	}
 }
-- 
1.9.1

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