Re: [PATCH] compat: Fix endian issue in union sigval

[Catalin Marinas]

cc'ing linux-arch as well.

On Tue, Feb 10, 2015 at 10:10:11AM +0000, Zhang Jian(Bamvor) wrote:
> In 64bit architecture, sigval_int is the high 32bit of sigval_ptr in
> big endian kernel compare with low 32bit of sigval_ptr in little
> endian kernel. reference:
> 
>     typedef union sigval {
>         int sival_int;
>         void *sival_ptr;
>     } sigval_t;
> 
> During compat_mq_notify or compat_timer_create, kernel get sigval
> from user space by reading sigval.sival_int. This is correct in 32 bit
> kernel and in 64bit little endian kernel. And It is wrong in 64bit big
> endian kernel:
> It get the high 32bit of sigval_ptr and put it to low 32bit of
> sigval_ptr. And the high 32bit sigval_ptr in empty in arm 32bit user
> space struct. So, kernel lost the value of sigval_ptr.
> 
> The following patch get the sigval_ptr in stead of sigval_int in order
> to avoid endian issue.
> Test pass in arm64 big endian and little endian kernel.
> 
> Signed-off-by: Zhang Jian(Bamvor) <bamvor.zhangjian@xxxxxxxxxx>
> ---
>  ipc/compat_mq.c | 7 ++-----
>  kernel/compat.c | 6 ++----
>  2 files changed, 4 insertions(+), 9 deletions(-)
> 
> diff --git a/ipc/compat_mq.c b/ipc/compat_mq.c
> index ef6f91c..2e07343 100644
> --- a/ipc/compat_mq.c
> +++ b/ipc/compat_mq.c
> @@ -99,11 +99,8 @@ COMPAT_SYSCALL_DEFINE2(mq_notify, mqd_t, mqdes,
>  	if (u_notification) {
>  		struct sigevent n;
>  		p = compat_alloc_user_space(sizeof(*p));
> -		if (get_compat_sigevent(&n, u_notification))
> -			return -EFAULT;
> -		if (n.sigev_notify == SIGEV_THREAD)
> -			n.sigev_value.sival_ptr = compat_ptr(n.sigev_value.sival_int);
> -		if (copy_to_user(p, &n, sizeof(*p)))
> +		if (get_compat_sigevent(&n, u_notification) ||
> +		    copy_to_user(p, &n, sizeof(*p)))
>  			return -EFAULT;

The kernel doesn't need to interpret the sival_ptr value, it's something
to be passed to the notifier function as an argument. For the user's
convenience, it is a union of an int and ptr. So I think the original
SIGEV_THREAD check and compat_ptr() conversion here is wrong, it
shouldn't exist at all (it doesn't exist in compat_sys_timer_create
either). This hunk looks fine to me.

>  	}
>  	return sys_mq_notify(mqdes, p);
> diff --git a/kernel/compat.c b/kernel/compat.c
> index ebb3c36..13a0e5d 100644
> --- a/kernel/compat.c
> +++ b/kernel/compat.c
> @@ -871,16 +871,14 @@ COMPAT_SYSCALL_DEFINE4(clock_nanosleep, clockid_t, which_clock, int, flags,
>   * We currently only need the following fields from the sigevent
>   * structure: sigev_value, sigev_signo, sig_notify and (sometimes
>   * sigev_notify_thread_id).  The others are handled in user mode.
> - * We also assume that copying sigev_value.sival_int is sufficient
> - * to keep all the bits of sigev_value.sival_ptr intact.
>   */
>  int get_compat_sigevent(struct sigevent *event,
>  		const struct compat_sigevent __user *u_event)
>  {
>  	memset(event, 0, sizeof(*event));
>  	return (!access_ok(VERIFY_READ, u_event, sizeof(*u_event)) ||
> -		__get_user(event->sigev_value.sival_int,
> -			&u_event->sigev_value.sival_int) ||
> +		__get_user(*(long long*)event->sigev_value.sival_ptr,
> +			&u_event->sigev_value.sival_ptr) ||

I don't think this is correct because some (most) architectures use
sival_int here when copying to user and for a big endian compat they
would get 0 for sival_int (mips, powerpc).

I think the correct fix is in the arm64 code:

diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c
index e299de396e9b..32601939a3c8 100644
--- a/arch/arm64/kernel/signal32.c
+++ b/arch/arm64/kernel/signal32.c
@@ -154,8 +154,7 @@ int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from)
 	case __SI_TIMER:
 		 err |= __put_user(from->si_tid, &to->si_tid);
 		 err |= __put_user(from->si_overrun, &to->si_overrun);
-		 err |= __put_user((compat_uptr_t)(unsigned long)from->si_ptr,
-				   &to->si_ptr);
+		 err |= __put_user(from->si_int, &to->si_int);
 		break;
 	case __SI_POLL:
 		err |= __put_user(from->si_band, &to->si_band);
@@ -184,7 +183,7 @@ int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from)
 	case __SI_MESGQ: /* But this is */
 		err |= __put_user(from->si_pid, &to->si_pid);
 		err |= __put_user(from->si_uid, &to->si_uid);
-		err |= __put_user((compat_uptr_t)(unsigned long)from->si_ptr, &to->si_ptr);
+		err |= __put_user(from->si_int, &to->si_int);
 		break;
 	case __SI_SYS:
 		err |= __put_user((compat_uptr_t)(unsigned long)

But we need to check other architectures that are capable of big endian
and have a compat layer.

-- 
Catalin
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