On Fri, Sep 22, 2017 at 5:00 AM, Baolin Wang baolin.wang@linaro.org wrote:
On 21 September 2017 at 21:09, Arnd Bergmann arnd@arndb.de wrote:
On Thu, Sep 21, 2017 at 8:18 AM, Baolin Wang baolin.wang@linaro.org wrote:
+static int snd_timer_user_tread(void __user *argp, struct snd_timer_user *tu,
unsigned int cmd)+{
int __user *p = argp;int xarg, old_tread;if (tu->timeri) /* too late */return -EBUSY;if (get_user(xarg, p))return -EFAULT;old_tread = tu->tread;+#if __BITS_PER_LONG == 64
tu->tread = xarg ? 2 : 0;+#ifdef IA32_EMULATION
tu->tread = xarg ? 3 : 0;+#endif +#else
if (cmd == SNDRV_TIMER_IOCTL_TREAD64)tu->tread = xarg ? 2 : 0;elsetu->tread = xarg ? 1 : 0;+#endif
The 64-bit case looks broken here:
- The tread flag is different for compat and native mode, so you must pass a flag to identify whether you are called from __snd_timer_user_ioctl or from snd_timer_user_ioctl_compat().
I have some confusion here. For 64-bit, we will set tu->tread = 2 no matter it is native mode or compat mode, only we will set tu->tread = 3 for x86_32 in compat mode, right? So I think we do not need to identify whether called from native mode or compat mode.
When we have a user space program with 32-bit time_t in compat mode (i.e. cmd==SNDRV_TIMER_IOCTL_TREAD) on a 64-bit kernel, we want to set tread=1, and that is different from the native mode that wants to set tread=2.
For determining whether to use tread=2 or tread=3, we have to check both compat mode and x32 mode. This could be done by checking for "if (IS_ENABLED(CONFIG_IA32_EMULATION) && in_compat_syscall() && is_x32_task())", but the in_compat_syscall() check can be skipped when you know that you were called from .compat_ioct().
Arnd