From: Kyle McMartin <kyle@shortfin.cabal.ca>
Date: Sat, 1 Mar 2008 18:25:52 +0000 (-0800)
Subject: [PARISC] futex: special case cmpxchg NULL in kernel space
X-Git-Tag: v2.6.25-rc6~1^2~3
X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=c20a84c91048c76c1379011c96b1a5cee5c7d9a0;p=linux-2.6-omap-h63xx.git

[PARISC] futex: special case cmpxchg NULL in kernel space

Commit a0c1e9073ef7428a14309cba010633a6cd6719ea added code to futex.c
to detect whether futex_atomic_cmpxchg_inatomic was implemented at run
time:

+       curval = cmpxchg_futex_value_locked(NULL, 0, 0);
+       if (curval == -EFAULT)
+               futex_cmpxchg_enabled = 1;

This is bogus on parisc, since page zero in kernel virtual space is the
gateway page for syscall entry, and should not be read from the kernel.
(That, and we really don't like the kernel faulting on its own address
 space...)

Signed-off-by: Kyle McMartin <kyle@mcmartin.ca>
---

diff --git a/include/asm-parisc/futex.h b/include/asm-parisc/futex.h
index dbee6e60aa8..fdc6d055ef7 100644
--- a/include/asm-parisc/futex.h
+++ b/include/asm-parisc/futex.h
@@ -56,6 +56,12 @@ futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
 	int err = 0;
 	int uval;
 
+	/* futex.c wants to do a cmpxchg_inatomic on kernel NULL, which is
+	 * our gateway page, and causes no end of trouble...
+	 */
+	if (segment_eq(KERNEL_DS, get_fs()) && !uaddr)
+		return -EFAULT;
+
 	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(int)))
 		return -EFAULT;
 
@@ -67,5 +73,5 @@ futex_atomic_cmpxchg_inatomic(int __user *uaddr, int oldval, int newval)
 	return uval;
 }
 
-#endif
-#endif
+#endif /*__KERNEL__*/
+#endif /*_ASM_PARISC_FUTEX_H*/