linux-kernel - Re: [PATCH] Kconfig: enhance DEFAULT_MMAP_MIN

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Date:	Wed, 16 Apr 2008 19:36:36 +0200
From:	maximilian attems <max@...o.at>
To:	Eric Paris <eparis@...hat.com>
Cc:	James Morris <jmorris@...ei.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Russell King <rmk+kernel@....linux.org.uk>,
	Martin Michlmayr <tbm@...ius.com>,
	Gordon Farquharson <gordonfarquharson@...il.com>
Subject: Re: [PATCH] Kconfig: enhance DEFAULT_MMAP_MIN_ADDR description

Got burned by setting the proposed default of 65536
across all Debian archs.

Thus proposing to be more specific on which archs you may
set this. Also propose a value for arm and friends that
doesn't break sshd.

Reword to mention working archs ia64 and ppc64 too.

Signed-off-by: maximilian attems <max@...o.at>
Cc: Martin Michlmayr <tbm@...ius.com>
Cc: Gordon Farquharson <gordonfarquharson@...il.com>
Acked-by: Eric Paris <eparis@...hat.com>

diff --git a/security/Kconfig b/security/Kconfig
index 5dfc206..49b51f9 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -113,10 +113,12 @@ config SECURITY_DEFAULT_MMAP_MIN_ADDR
 	  from userspace allocation.  Keeping a user from writing to low pages
 	  can help reduce the impact of kernel NULL pointer bugs.
 
-	  For most users with lots of address space a value of 65536 is
-	  reasonable and should cause no problems.  Programs which use vm86
-	  functionality would either need additional permissions from either
-	  the LSM or the capabilities module or have this protection disabled.
+	  For most ia64, ppc64 and x86 users with lots of address space
+	  a value of 65536 is reasonable and should cause no problems.
+	  On arm and other archs it should not be higher than 32768.
+	  Programs which use vm86 functionality would either need additional
+	  permissions from either the LSM or the capabilities module or have
+	  this protection disabled.
 
 	  This value can be changed after boot using the
 	  /proc/sys/vm/mmap_min_addr tunable.
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