[patch 02/31] i386: fix file_read_actor() and pipe_read() for original i386 systems

Greg KH
2007-04-11T22:54:42Z

[-- Attachment #1: i386-fix-file_read_actor-and-pipe_read-for-original-i386-systems.patch --]
[-- Type: text/plain, Size: 1826 bytes --]

-stable review patch. If anyone has any objections, please let us know.

------------------
From: Thomas Gleixner <tglx@linutronix.de>

The __copy_to_user_inatomic() calls in file_read_actor() and pipe_read()
are broken on original i386 machines, where WP-works-ok == false, as
__copy_to_user_inatomic() on such systems calls functions which might
sleep and/or contain cond_resched() calls inside of a kmap_atomic()
region.

The original check for WP-works-ok was in access_ok(), but got moved
during the 2.5 series to fix a race vs. swap.

Return the number of bytes to copy in the case where we are in an atomic
region, so the non atomic code pathes in file_read_actor() and
pipe_read() are taken.

This could be optimized to avoid the kmap_atomic by moving the check for
WP-works-ok into fault_in_pages_writeable(), but this is more intrusive
and can be done later.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
arch/i386/lib/usercopy.c | 9 +++++++++
1 file changed, 9 insertions(+)

--- a/arch/i386/lib/usercopy.c
+++ b/arch/i386/lib/usercopy.c
@@ -10,6 +10,7 @@
#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/backing-dev.h>
+#include <linux/interrupt.h>
#include <asm/uaccess.h>
#include <asm/mmx.h>

@@ -719,6 +720,14 @@ unsigned long __copy_to_user_ll(void __u
#ifndef CONFIG_X86_WP_WORKS_OK
if (unlikely(boot_cpu_data.wp_works_ok == 0) &&
((unsigned long )to) < TASK_SIZE) {
+ /*
+ * When we are in an atomic section (see
+ * mm/filemap.c:file_read_actor), return the full
+ * length to take the slow path.
+ */
+ if (in_atomic())
+ return n;
+
/*
* CPU does not honor the WP bit when writing
* from supervisory mode, and due to preemption or SMP,

--