Many drivers have ioctl() handlers that are completely compatible between 32-bit and 64-bit architectures, except for the argument that is passed down from user space and may have to be passed through compat_ptr() in order to become a valid 64-bit pointer.
Using ".compat_ptr = compat_ptr_ioctl" in file operations should let us simplify a lot of those drivers to avoid #ifdef checks, and convert additional drivers that don't have proper compat handling yet.
On most architectures, the compat_ptr_ioctl() just passes all arguments to the corresponding ->ioctl handler. The exception is arch/s390, where compat_ptr() clears the top bit of a 32-bit pointer value, so user space pointers to the second 2GB alias the first 2GB, as is the case for native 32-bit s390 user space.
The compat_ptr_ioctl() function must therefore be used only with ioctl functions that either ignore the argument or pass a pointer to a compatible data type.
If any ioctl command handled by fops->unlocked_ioctl passes a plain integer instead of a pointer, or any of the passed data types is incompatible between 32-bit and 64-bit architectures, a proper handler is required instead of compat_ptr_ioctl.
Signed-off-by: Arnd Bergmann arnd@arndb.de --- v3: add a better description v2: use compat_ptr_ioctl instead of generic_compat_ioctl_ptrarg, as suggested by Al Viro --- fs/ioctl.c | 35 +++++++++++++++++++++++++++++++++++ include/linux/fs.h | 7 +++++++ 2 files changed, 42 insertions(+)
diff --git a/fs/ioctl.c b/fs/ioctl.c index 9d26251f34a9..812061ba667a 100644 --- a/fs/ioctl.c +++ b/fs/ioctl.c @@ -8,6 +8,7 @@ #include <linux/syscalls.h> #include <linux/mm.h> #include <linux/capability.h> +#include <linux/compat.h> #include <linux/file.h> #include <linux/fs.h> #include <linux/security.h> @@ -748,3 +749,37 @@ SYSCALL_DEFINE3(ioctl, unsigned int, fd, unsigned int, cmd, unsigned long, arg) { return ksys_ioctl(fd, cmd, arg); } + +#ifdef CONFIG_COMPAT +/** + * compat_ptr_ioctl - generic implementation of .compat_ioctl file operation + * + * This is not normally called as a function, but instead set in struct + * file_operations as + * + * .compat_ioctl = compat_ptr_ioctl, + * + * On most architectures, the compat_ptr_ioctl() just passes all arguments + * to the corresponding ->ioctl handler. The exception is arch/s390, where + * compat_ptr() clears the top bit of a 32-bit pointer value, so user space + * pointers to the second 2GB alias the first 2GB, as is the case for + * native 32-bit s390 user space. + * + * The compat_ptr_ioctl() function must therefore be used only with ioctl + * functions that either ignore the argument or pass a pointer to a + * compatible data type. + * + * If any ioctl command handled by fops->unlocked_ioctl passes a plain + * integer instead of a pointer, or any of the passed data types + * is incompatible between 32-bit and 64-bit architectures, a proper + * handler is required instead of compat_ptr_ioctl. + */ +long compat_ptr_ioctl(struct file *file, unsigned int cmd, unsigned long arg) +{ + if (!file->f_op->unlocked_ioctl) + return -ENOIOCTLCMD; + + return file->f_op->unlocked_ioctl(file, cmd, (unsigned long)compat_ptr(arg)); +} +EXPORT_SYMBOL(compat_ptr_ioctl); +#endif diff --git a/include/linux/fs.h b/include/linux/fs.h index e0d909d35763..0b4d8fc79e0f 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1727,6 +1727,13 @@ int vfs_mkobj(struct dentry *, umode_t,
extern long vfs_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
+#ifdef CONFIG_COMPAT +extern long compat_ptr_ioctl(struct file *file, unsigned int cmd, + unsigned long arg); +#else +#define compat_ptr_ioctl NULL +#endif + /* * VFS file helper functions. */