On 08/16/2011 06:54 PM, Yong Zhang wrote:
We can't trust in the caller(userspace) to give signed-extend
parameter, thus futex-wait may fail in some special case.
For example, if 'val' is too big and bit-31 is 1,
the caller may enter endless loop at:
futex_wait_setup()
{
...
if (uval != val) {
queue_unlock(q, *hb);
ret = -EWOULDBLOCK;
...
}
Below assembler code will make it more easy to understand how
the patch take effect :)
Dump of assembler code for function SyS_32_futex:
0xffffffff811b6fe8<+0>: sll a1,a1,0x0
0xffffffff811b6fec<+4>: sll a2,a2,0x0
0xffffffff811b6ff0<+8>: j 0xffffffff8121a240<compat_sys_futex>
0xffffffff811b6ff4<+12>: sll a5,a5,0x0
Signed-off-by: Yong Zhang<yong.zhang@xxxxxxxxxxxxx>
Cc: Ralf Baechle<ralf@xxxxxxxxxxxxxx>
---
arch/mips/kernel/linux32.c | 7 +++++++
arch/mips/kernel/scall64-n32.S | 2 +-
arch/mips/kernel/scall64-o32.S | 2 +-
3 files changed, 9 insertions(+), 2 deletions(-)
[...]
diff --git a/arch/mips/kernel/linux32.c b/arch/mips/kernel/linux32.c
index 876a75c..922a554 100644
--- a/arch/mips/kernel/linux32.c
+++ b/arch/mips/kernel/linux32.c
@@ -349,3 +349,10 @@ SYSCALL_DEFINE6(32_fanotify_mark, int, fanotify_fd, unsigned int, flags,
return sys_fanotify_mark(fanotify_fd, flags, merge_64(a3, a4),
dfd, pathname);
}
+
+SYSCALL_DEFINE6(32_futex, u32 __user *, uaddr, int, op, u32, val,
+ struct compat_timespec __user *, utime, u32 __user *, uaddr2,
+ u32, val3)
+{
+ return compat_sys_futex(uaddr, op, val, utime, uaddr2, val3);
+}
diff --git a/arch/mips/kernel/scall64-n32.S b/arch/mips/kernel/scall64-n32.S
index b85842f..c956cc9 100644
--- a/arch/mips/kernel/scall64-n32.S
+++ b/arch/mips/kernel/scall64-n32.S
@@ -315,7 +315,7 @@ EXPORT(sysn32_call_table)
PTR sys_fremovexattr
PTR sys_tkill
PTR sys_ni_syscall
- PTR compat_sys_futex
+ PTR sys_32_futex
PTR compat_sys_sched_setaffinity /* 6195 */
PTR compat_sys_sched_getaffinity
PTR sys_cacheflush
diff --git a/arch/mips/kernel/scall64-o32.S b/arch/mips/kernel/scall64-o32.S
index 46c4763..f48b18e 100644
--- a/arch/mips/kernel/scall64-o32.S
+++ b/arch/mips/kernel/scall64-o32.S
@@ -441,7 +441,7 @@ sys_call_table:
PTR sys_fremovexattr /* 4235 */
PTR sys_tkill
PTR sys_sendfile64
- PTR compat_sys_futex
+ PTR sys_32_futex
This change is redundant, scall64-o32.S already does the right thing
so additional zero extending is not needed and is just extra
instructions to execute for no reason.
PTR compat_sys_sched_setaffinity
PTR compat_sys_sched_getaffinity /* 4240 */
PTR compat_sys_io_setup
But really I think this patch fixes things at the wrong level. Each
architecture potentially needs a similar patch. What would happen if
we did something like:
diff --git a/kernel/futex_compat.c b/kernel/futex_compat.c
index 5f9e689..74ada65 100644
--- a/kernel/futex_compat.c
+++ b/kernel/futex_compat.c
@@ -180,9 +180,9 @@ err_unlock:
return ret;
}
-asmlinkage long compat_sys_futex(u32 __user *uaddr, int op, u32 val,
- struct compat_timespec __user *utime, u32 __user *uaddr2,
- u32 val3)
+SYSCALL_DEFINE6(compat_sys_futex, u32 __user *, uaddr, int , op, u32, val,
+ struct compat_timespec __user *, utime, u32 __user *, uaddr2,
+ u32, val3)
{
struct timespec ts;
ktime_t t, *tp = NULL;
Obviously the function name is wrong, but a varient of
SYSCALL_DEFINE*() could be created so the proper function names are
produced.
David Daney
