linux-kernel - [PATCH] powerpc/mm: remove hack in mmap randomize layout

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <1318882661-26859-1-git-send-email-dpmcgee@gmail.com>
Date:	Mon, 17 Oct 2011 15:17:36 -0500
From:	Dan McGee <dpmcgee@...il.com>
To:	linuxppc-dev@...ts.ozlabs.org
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Dan McGee <dpmcgee@...il.com>, linux-kernel@...r.kernel.org
Subject: [PATCH] powerpc/mm: remove hack in mmap randomize layout

Since commit 8a0a9bd4db63bc45e301, this comment in mmap_rnd() does not
hold true as the value returned by get_random_int() will in fact be
different every single call. Remove the comment and simplify the code
back to its original desired form.

This reverts commit a5adc91a4b44b5d1 which is no longer necessary.

Signed-off-by: Dan McGee <dpmcgee@...il.com>
---
 arch/powerpc/mm/mmap_64.c |   14 +++-----------
 1 files changed, 3 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/mm/mmap_64.c b/arch/powerpc/mm/mmap_64.c
index 5a783d8..67a42ed 100644
--- a/arch/powerpc/mm/mmap_64.c
+++ b/arch/powerpc/mm/mmap_64.c
@@ -53,14 +53,6 @@ static inline int mmap_is_legacy(void)
 	return sysctl_legacy_va_layout;
 }
 
-/*
- * Since get_random_int() returns the same value within a 1 jiffy window,
- * we will almost always get the same randomisation for the stack and mmap
- * region. This will mean the relative distance between stack and mmap will
- * be the same.
- *
- * To avoid this we can shift the randomness by 1 bit.
- */
 static unsigned long mmap_rnd(void)
 {
 	unsigned long rnd = 0;
@@ -68,11 +60,11 @@ static unsigned long mmap_rnd(void)
 	if (current->flags & PF_RANDOMIZE) {
 		/* 8MB for 32bit, 1GB for 64bit */
 		if (is_32bit_task())
-			rnd = (long)(get_random_int() % (1<<(22-PAGE_SHIFT)));
+			rnd = (long)(get_random_int() % (1<<(23-PAGE_SHIFT)));
 		else
-			rnd = (long)(get_random_int() % (1<<(29-PAGE_SHIFT)));
+			rnd = (long)(get_random_int() % (1<<(30-PAGE_SHIFT)));
 	}
-	return (rnd << PAGE_SHIFT) * 2;
+	return rnd << PAGE_SHIFT;
 }
 
 static inline unsigned long mmap_base(void)
-- 
1.7.7

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/