From: Al Viro <viro@ZenIV.linux.org.uk>
Date: Sun, 1 Sep 2013 19:35:01 +0000 (+0100)
Subject: Introduce [compat_]save_altstack_ex() to unbreak x86 SMAP
X-Git-Tag: v3.12-rc1~153^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=bd1c149aa9915b9abb6d83d0f01dfd2ace0680b5;p=pandora-kernel.git

Introduce [compat_]save_altstack_ex() to unbreak x86 SMAP

For performance reasons, when SMAP is in use, SMAP is left open for an
entire put_user_try { ... } put_user_catch(); block, however, calling
__put_user() in the middle of that block will close SMAP as the
STAC..CLAC constructs intentionally do not nest.

Furthermore, using __put_user() rather than put_user_ex() here is bad
for performance.

Thus, introduce new [compat_]save_altstack_ex() helpers that replace
__[compat_]save_altstack() for x86, being currently the only
architecture which supports put_user_try { ... } put_user_catch().

Reported-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: <stable@vger.kernel.org> # v3.8+
Link: http://lkml.kernel.org/n/tip-es5p6y64if71k8p5u08agv9n@git.kernel.org
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