ARM: 9108/1: oabi-compat: rework epoll_wait/epoll_pwait emulation

The epoll_wait() system call wrapper is one of the remaining users of
the set_fs() infrasturcture for Arm. Changing it to not require set_fs()
is rather complex unfortunately.

The approach I'm taking here is to allow architectures to override
the code that copies the output to user space, and let the oabi-compat
implementation check whether it is getting called from an EABI or OABI
system call based on the thread_info->syscall value.

The in_oabi_syscall() check here mirrors the in_compat_syscall() and
in_x32_syscall() helpers for 32-bit compat implementations on other
architectures.

Overall, the amount of code goes down, at least with the newly added
sys_oabi_epoll_pwait() helper getting removed again. The downside
is added complexity in the source code for the native implementation.
There should be no difference in runtime performance except for Arm
kernels with CONFIG_OABI_COMPAT enabled that now have to go through
an external function call to check which of the two variants to use.

Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

1 files changed, 16 insertions, 67 deletions

diff --git a/arch/arm/kernel/sys_oabi-compat.c b/arch/arm/kernel/sys_oabi-compat.c
index 443203fafb6b..1f6a433200f1 100644
--- a/arch/arm/kernel/sys_oabi-compat.c
+++ b/arch/arm/kernel/sys_oabi-compat.c
@@ -83,6 +83,8 @@
 #include <linux/uaccess.h>
 #include <linux/slab.h>
 
+#include <asm/syscall.h>
+
 struct oldabi_stat64 {
 	unsigned long long st_dev;
 	unsigned int	__pad1;
@@ -264,87 +266,34 @@ asmlinkage long sys_oabi_epoll_ctl(int epfd, int op, int fd,
 
 	return do_epoll_ctl(epfd, op, fd, &kernel, false);
 }
-
-static long do_oabi_epoll_wait(int epfd, struct oabi_epoll_event __user *events,
-			       int maxevents, int timeout)
-{
-	struct epoll_event *kbuf;
-	struct oabi_epoll_event e;
-	mm_segment_t fs;
-	long ret, err, i;
-
-	if (maxevents <= 0 ||
-			maxevents > (INT_MAX/sizeof(*kbuf)) ||
-			maxevents > (INT_MAX/sizeof(*events)))
-		return -EINVAL;
-	if (!access_ok(events, sizeof(*events) * maxevents))
-		return -EFAULT;
-	kbuf = kmalloc_array(maxevents, sizeof(*kbuf), GFP_KERNEL);
-	if (!kbuf)
-		return -ENOMEM;
-	fs = get_fs();
-	set_fs(KERNEL_DS);
-	ret = sys_epoll_wait(epfd, kbuf, maxevents, timeout);
-	set_fs(fs);
-	err = 0;
-	for (i = 0; i < ret; i++) {
-		e.events = kbuf[i].events;
-		e.data = kbuf[i].data;
-		err = __copy_to_user(events, &e, sizeof(e));
-		if (err)
-			break;
-		events++;
-	}
-	kfree(kbuf);
-	return err ? -EFAULT : ret;
-}
 #else
 asmlinkage long sys_oabi_epoll_ctl(int epfd, int op, int fd,
 				   struct oabi_epoll_event __user *event)
 {
 	return -EINVAL;
 }
-
-asmlinkage long sys_oabi_epoll_wait(int epfd,
-				    struct oabi_epoll_event __user *events,
-				    int maxevents, int timeout)
-{
-	return -EINVAL;
-}
 #endif
 
-SYSCALL_DEFINE4(oabi_epoll_wait, int, epfd,
-		struct oabi_epoll_event __user *, events,
-		int, maxevents, int, timeout)
+struct epoll_event __user *
+epoll_put_uevent(__poll_t revents, __u64 data,
+		 struct epoll_event __user *uevent)
 {
-	return do_oabi_epoll_wait(epfd, events, maxevents, timeout);
-}
+	if (in_oabi_syscall()) {
+		struct oabi_epoll_event __user *oevent = (void __user *)uevent;
 
-/*
- * Implement the event wait interface for the eventpoll file. It is the kernel
- * part of the user space epoll_pwait(2).
- */
-SYSCALL_DEFINE6(oabi_epoll_pwait, int, epfd,
-		struct oabi_epoll_event __user *, events, int, maxevents,
-		int, timeout, const sigset_t __user *, sigmask,
-		size_t, sigsetsize)
-{
-	int error;
+		if (__put_user(revents, &oevent->events) ||
+		    __put_user(data, &oevent->data))
+			return NULL;
 
-	/*
-	 * If the caller wants a certain signal mask to be set during the wait,
-	 * we apply it here.
-	 */
-	error = set_user_sigmask(sigmask, sigsetsize);
-	if (error)
-		return error;
+		return (void __user *)(oevent+1);
+	}
 
-	error = do_oabi_epoll_wait(epfd, events, maxevents, timeout);
-	restore_saved_sigmask_unless(error == -EINTR);
+	if (__put_user(revents, &uevent->events) ||
+	    __put_user(data, &uevent->data))
+		return NULL;
 
-	return error;
+	return uevent+1;
 }
-#endif
 
 struct oabi_sembuf {
 	unsigned short	sem_num;