[PATCH] i386 / desc_empty macro is incorrect

[Chris Wright <chrisw@osdl.org>]

From: Zachary Amsden <zach@vmware.com>

Chuck Ebbert wrote:
>     I think that should be "|" instead of "+".

I think so too.  I merely moved the code here and didn't notice it in 
all this excitement.

0x00cf9a000xff306600  =>

Present CPL-0 32-bit code segment, base 0x0000ff30, limit 0xf6601 pages, 
for which desc_empty(desc) is true.

Thankfully, this is not used as a security check, but it can falsely 
overwrite TLS segments with carefully chosen base / limits.  I do not 
believe this is an issue in practice, but it is a kernel bug.

Nice catch.  Looks like it affects all 2.6.X kernels.

Chuck Ebbert noticed that the desc_empty macro is incorrect.  Fix it.

Signed-off-by: Zachary Amsden <zach@vmware.com>
Signed-off-by: Chris Wright <chrisw@osdl.org>
---

diff --git a/include/asm-i386/processor.h b/include/asm-i386/processor.h
--- a/include/asm-i386/processor.h
+++ b/include/asm-i386/processor.h
@@ -29,7 +29,7 @@ struct desc_struct {
 };
 
 #define desc_empty(desc) \
-		(!((desc)->a + (desc)->b))
+		(!((desc)->a | (desc)->b))
 
 #define desc_equal(desc1, desc2) \
 		(((desc1)->a == (desc2)->a) && ((desc1)->b == (desc2)->b))