linux/arch/x86
Linus Torvalds 42a886af72 x86-64: Fix "bytes left to copy" return value for copy_from_user()
Most users by far do not care about the exact return value (they only
really care about whether the copy succeeded in its entirety or not),
but a few special core routines actually care deeply about exactly how
many bytes were copied from user space.

And the unrolled versions of the x86-64 user copy routines would
sometimes report that it had copied more bytes than it actually had.

Very few uses actually have partial copies to begin with, but to make
this bug even harder to trigger, most x86 CPU's use the "rep string"
instructions for normal user copies, and that version didn't have this
issue.

To make it even harder to hit, the one user of this that really cared
about the return value (and used the uncached version of the copy that
doesn't use the "rep string" instructions) was the generic write
routine, which pre-populated its source, once more hiding the problem by
avoiding the exception case that triggers the bug.

In other words, very special thanks to Bron Gondwana who not only
triggered this, but created a test-program to show it, and bisected the
behavior down to commit 08291429cf ("mm:
fix pagecache write deadlocks") which changed the access pattern just
enough that you can now trigger it with 'writev()' with multiple
iovec's.

That commit itself was not the cause of the bug, it just allowed all the
stars to align just right that you could trigger the problem.

[ Side note: this is just the minimal fix to make the copy routines
  (with __copy_from_user_inatomic_nocache as the particular version that
  was involved in showing this) have the right return values.

  We really should improve on the exceptional case further - to make the
  copy do a byte-accurate copy up to the exact page limit that causes it
  to fail.  As it is, the callers have to do extra work to handle the
  limit case gracefully. ]

Reported-by: Bron Gondwana <brong@fastmail.fm>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

 (which didn't have this problem), and since
most users that do the carethis was very hard to trigger, but
2008-06-17 17:47:50 -07:00
..
boot x86: fix unused variable 'loops' warning in arch/x86/boot/a20.c 2008-06-12 21:27:05 +02:00
configs x86: add optimized inlining 2008-04-26 17:44:55 +02:00
crypto [CRYPTO] aes-x86-32: Remove unused return code 2008-04-21 10:19:21 +08:00
ia32 signals: x86 TS_RESTORE_SIGMASK 2008-04-30 08:29:37 -07:00
kernel Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jbarnes/pci-2.6 2008-06-14 13:32:56 -07:00
kvm KVM: MMU: Fix is_empty_shadow_page() check 2008-06-06 21:36:33 +03:00
lguest lguest: fix ugly <NULL> in /proc/interrupts 2008-05-30 15:09:43 +10:00
lib x86-64: Fix "bytes left to copy" return value for copy_from_user() 2008-06-17 17:47:50 -07:00
mach-default spelling fixes: arch/i386/ 2007-10-20 01:13:56 +02:00
mach-es7000 i386: es7000 minor cleanups 2007-10-17 20:16:15 +02:00
mach-generic x86: coding style fixes to arch/x86/mach-generic/bigsmp.c 2008-04-17 17:40:48 +02:00
mach-rdc321x x86, rdc321x: remove watchdog file 2008-04-17 17:40:50 +02:00
mach-visws x86: fix compilation error in VisWS 2008-04-24 23:15:44 +02:00
mach-voyager x86, voyager: fix ioremap_nocache() 2008-04-30 23:15:34 +02:00
math-emu x86: fix broken math-emu with lazy allocation of fpu area 2008-06-04 13:11:46 +02:00
mm Merge branch 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2008-06-12 12:55:32 -07:00
oprofile x86: oprofile: remove NR_CPUS arrays in arch/x86/oprofile/nmi_int.c 2008-04-19 19:44:58 +02:00
pci Merge branch 'pci-for-jesse' of git://git.kernel.org/pub/scm/linux/kernel/git/x86/linux-2.6-tip into for-linus 2008-06-12 13:51:05 -07:00
power x86: coding style fixes to arch/x86/power/cpu_32.c 2008-04-17 17:40:50 +02:00
vdso x86: use explicit copy in vdso_gettimeofday() 2008-05-23 14:08:06 +02:00
video x86: video/fbdev.c: add MODULE_LICENSE 2008-05-04 20:04:46 +02:00
xen common implementation of iterative div/mod 2008-06-12 10:47:56 +02:00
Kconfig PCI/x86: fix up PCI stuff so that PCI_GOANY supports OLPC 2008-06-05 14:29:25 -07:00
Kconfig.cpu x86: CONFIG_X86_ELAN fix 2008-04-30 23:15:35 +02:00
Kconfig.debug x86: fix CONFIG_NONPROMISC_DEVMEM prompt and help text 2008-06-05 14:21:45 -07:00
Makefile x86: add subarch support (for headers) to x86_64 2008-04-17 17:41:01 +02:00
Makefile_32.cpu x86: move i386 and x86_64 Makefiles to arch/x86 2007-10-25 22:27:34 +02:00