Re: [PATCH v3 01/17] y2038: asm-generic: Extend sysvipc data structures

Eric W. Biederman
2018-04-19T14:59:48Z

Arnd Bergmann <arnd@arndb.de> writes:

> Most architectures now use the asm-generic copy of the sysvipc data
> structures (msqid64_ds, semid64_ds, shmid64_ds), which use 32-bit
> __kernel_time_t on 32-bit architectures but have padding behind them to
> allow extending the type to 64-bit.
>
> Unfortunately, that fails on all big-endian architectures, which have the
> padding on the wrong side. As so many of them get it wrong, we decided to
> not bother even trying to fix it up when we introduced the asm-generic
> copy. Instead we always use the padding word now to provide the upper
> 32 bits of the seconds value, regardless of the endianess.
>
> A libc implementation on a typical big-endian system can deal with
> this by providing its own copy of the structure definition to user
> space, and swapping the two 32-bit words before returning from the
> semctl/shmctl/msgctl system calls.
>
> ARM64 and s/390 are architectures that use these generic headers and
> also provide support for compat mode on 64-bit kernels, so we adapt
> their copies here as well.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> include/uapi/asm-generic/msgbuf.h | 17 ++++++++---------
> include/uapi/asm-generic/sembuf.h | 26 ++++++++++++++++----------
> include/uapi/asm-generic/shmbuf.h | 17 ++++++++---------
> 3 files changed, 32 insertions(+), 28 deletions(-)
>
> diff --git a/include/uapi/asm-generic/msgbuf.h b/include/uapi/asm-generic/msgbuf.h
> index fb306ebdb36f..d2169cae93b8 100644
> --- a/include/uapi/asm-generic/msgbuf.h
> +++ b/include/uapi/asm-generic/msgbuf.h
> @@ -18,23 +18,22 @@
> * On big-endian systems, the padding is in the wrong place.
> *
> * Pad space is left for:
> - * - 64-bit time_t to solve y2038 problem
> * - 2 miscellaneous 32-bit values
> */
>
> struct msqid64_ds {
> struct ipc64_perm msg_perm;
> +#if __BITS_PER_LONG == 64
> __kernel_time_t msg_stime; /* last msgsnd time */
> -#if __BITS_PER_LONG != 64
> - unsigned long __unused1;
> -#endif
> __kernel_time_t msg_rtime; /* last msgrcv time */
> -#if __BITS_PER_LONG != 64
> - unsigned long __unused2;
> -#endif
> __kernel_time_t msg_ctime; /* last change time */
> -#if __BITS_PER_LONG != 64
> - unsigned long __unused3;
> +#else
> + unsigned long msg_stime; /* last msgsnd time */
> + unsigned long msg_stime_high;
> + unsigned long msg_rtime; /* last msgrcv time */
> + unsigned long msg_rtime_high;
> + unsigned long msg_ctime; /* last change time */
> + unsigned long msg_ctime_high;
> #endif

I suspect you want to use __kernel_ulong_t here instead of a raw
unsigned long. If nothing else it seems inconsistent to use typedefs
in one half of the structure and no typedefs in the other half.

> __kernel_ulong_t msg_cbytes; /* current number of bytes on queue */
> __kernel_ulong_t msg_qnum; /* number of messages in queue */
> diff --git a/include/uapi/asm-generic/sembuf.h b/include/uapi/asm-generic/sembuf.h
> index cbf9cfe977d6..0bae010f1b64 100644
> --- a/include/uapi/asm-generic/sembuf.h
> +++ b/include/uapi/asm-generic/sembuf.h
> @@ -13,23 +13,29 @@
> * everyone just ended up making identical copies without specific
> * optimizations, so we may just as well all use the same one.
> *
> - * 64 bit architectures typically define a 64 bit __kernel_time_t,
> + * 64 bit architectures use a 64-bit __kernel_time_t here, while
> + * 32 bit architectures have a pair of unsigned long values.
> * so they do not need the first two padding words.
> - * On big-endian systems, the padding is in the wrong place.
> *
> - * Pad space is left for:
> - * - 64-bit time_t to solve y2038 problem
> - * - 2 miscellaneous 32-bit values
> + * On big-endian systems, the padding is in the wrong place for
> + * historic reasons, so user space has to reconstruct a time_t
> + * value using
> + *
> + * user_semid_ds.sem_otime = kernel_semid64_ds.sem_otime +
> + * ((long long)kernel_semid64_ds.sem_otime_high << 32)
> + *
> + * Pad space is left for 2 miscellaneous 32-bit values
> */
> struct semid64_ds {
> struct ipc64_perm sem_perm; /* permissions .. see ipc.h */
> +#if __BITS_PER_LONG == 64
> __kernel_time_t sem_otime; /* last semop time */
> -#if __BITS_PER_LONG != 64
> - unsigned long __unused1;
> -#endif
> __kernel_time_t sem_ctime; /* last change time */
> -#if __BITS_PER_LONG != 64
> - unsigned long __unused2;
> +#else
> + unsigned long sem_otime; /* last semop time */
> + unsigned long sem_otime_high;
> + unsigned long sem_ctime; /* last change time */
> + unsigned long sem_ctime_high;
> #endif
> unsigned long sem_nsems; /* no. of semaphores in array */
> unsigned long __unused3;
> diff --git a/include/uapi/asm-generic/shmbuf.h b/include/uapi/asm-generic/shmbuf.h
> index 2b6c3bb97f97..602f1b5b462b 100644
> --- a/include/uapi/asm-generic/shmbuf.h
> +++ b/include/uapi/asm-generic/shmbuf.h
> @@ -19,24 +19,23 @@
> *
> *
> * Pad space is left for:
> - * - 64-bit time_t to solve y2038 problem
> * - 2 miscellaneous 32-bit values
> */
>
> struct shmid64_ds {
> struct ipc64_perm shm_perm; /* operation perms */
> size_t shm_segsz; /* size of segment (bytes) */
> +#if __BITS_PER_LONG == 64
> __kernel_time_t shm_atime; /* last attach time */
> -#if __BITS_PER_LONG != 64
> - unsigned long __unused1;
> -#endif
> __kernel_time_t shm_dtime; /* last detach time */
> -#if __BITS_PER_LONG != 64
> - unsigned long __unused2;
> -#endif
> __kernel_time_t shm_ctime; /* last change time */
> -#if __BITS_PER_LONG != 64
> - unsigned long __unused3;
> +#else
> + unsigned long shm_atime; /* last attach time */
> + unsigned long shm_atime_high;
> + unsigned long shm_dtime; /* last detach time */
> + unsigned long shm_dtime_high;
> + unsigned long shm_ctime; /* last change time */
> + unsigned long shm_ctime_high;
> #endif
> __kernel_pid_t shm_cpid; /* pid of creator */
> __kernel_pid_t shm_lpid; /* pid of last operator */