Re: [Qemu-devel] [PATCH 14/18] linux-user: Use __get_user() and __put_user() to handle structs in do_fcntl()

[Laurent Vivier]

Le 06/06/2016 à 20:58, Peter Maydell a écrit :
> Use the __get_user() and __put_user() to handle reading and writing the
> guest structures in do_ioctl(). This has two benefits:
>  * avoids possible errors due to misaligned guest pointers
>  * correctly sign extends signed fields (like l_start in struct flock)
>    which might be different sizes between guest and host
> 
> To do this we abstract out into copy_from/to_user functions. We
> also standardize on always using host flock64 and the F_GETLK64
> etc flock commands, as this means we always have 64 bit offsets
> whether the host is 64-bit or 32-bit and we don't need to support
> conversion to both host struct flock and struct flock64.
> 
> In passing we fix errors in converting l_type from the host to
> the target (where we were doing a byteswap of the host value
> before trying to do the convert-bitmasks operation rather than
> otherwise, and inexplicably shifting left by 1).

I  think the ">> 1" is coming from:

43f238d Support fcntl F_GETLK64, F_SETLK64, F_SETLKW64

to convert arm to x86, and should have been removed then in:

2ba7f73 alpha-linux-user: Translate fcntl l_type

So yes, the ">> 1" is wrong. I don't understand how it can work.

> 
> Signed-off-by: Peter Maydell <address@hidden>
> ---
>  linux-user/syscall.c | 280 
> +++++++++++++++++++++++++++++----------------------
>  1 file changed, 157 insertions(+), 123 deletions(-)
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 4cf67c8..f3a487e 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -4894,11 +4894,11 @@ static int target_to_host_fcntl_cmd(int cmd)
>       case TARGET_F_SETFL:
>              return cmd;
>          case TARGET_F_GETLK:
> -         return F_GETLK;
> -     case TARGET_F_SETLK:
> -         return F_SETLK;
> -     case TARGET_F_SETLKW:
> -         return F_SETLKW;
> +            return F_GETLK64;
> +        case TARGET_F_SETLK:
> +            return F_SETLK64;
> +        case TARGET_F_SETLKW:
> +            return F_SETLKW64;
>       case TARGET_F_GETOWN:
>           return F_GETOWN;
>       case TARGET_F_SETOWN:

I see no reason to have this in this patch.

> @@ -4949,12 +4949,134 @@ static const bitmask_transtbl flock_tbl[] = {
>      { 0, 0, 0, 0 }
>  };
>  
> -static abi_long do_fcntl(int fd, int cmd, abi_ulong arg)
> +static inline abi_long copy_from_user_flock(struct flock64 *fl,
> +                                            abi_ulong target_flock_addr)
>  {
> -    struct flock fl;
>      struct target_flock *target_fl;
> +    short l_type;
> +
> +    if (!lock_user_struct(VERIFY_READ, target_fl, target_flock_addr, 1)) {
> +        return -TARGET_EFAULT;
> +    }
> +
> +    __get_user(l_type, &target_fl->l_type);
> +    fl->l_type = target_to_host_bitmask(l_type, flock_tbl);
> +    __get_user(fl->l_whence, &target_fl->l_whence);
> +    __get_user(fl->l_start, &target_fl->l_start);
> +    __get_user(fl->l_len, &target_fl->l_len);
> +    __get_user(fl->l_pid, &target_fl->l_pid);
> +    unlock_user_struct(target_fl, target_flock_addr, 0);
> +    return 0;
> +}
> +
> +static inline abi_long copy_to_user_flock(abi_ulong target_flock_addr,
> +                                          const struct flock64 *fl)
> +{
> +    struct target_flock *target_fl;
> +    short l_type;
> +
> +    if (!lock_user_struct(VERIFY_WRITE, target_fl, target_flock_addr, 0)) {
> +        return -TARGET_EFAULT;
> +    }
> +
> +    l_type = host_to_target_bitmask(fl->l_type, flock_tbl);
> +    __put_user(l_type, &target_fl->l_type);
> +    __put_user(fl->l_whence, &target_fl->l_whence);
> +    __put_user(fl->l_start, &target_fl->l_start);
> +    __put_user(fl->l_len, &target_fl->l_len);
> +    __put_user(fl->l_pid, &target_fl->l_pid);
> +    unlock_user_struct(target_fl, target_flock_addr, 1);
> +    return 0;
> +}
> +
> +typedef abi_long from_flock64_fn(struct flock64 *fl, abi_ulong target_addr);
> +typedef abi_long to_flock64_fn(abi_ulong target_addr, const struct flock64 
> *fl);
> +
> +#ifdef TARGET_ARM
> +static inline abi_long copy_from_user_eabi_flock64(struct flock64 *fl,
> +                                                   abi_ulong 
> target_flock_addr)
> +{
> +    struct target_eabi_flock64 *target_fl;
> +    short l_type;
> +
> +    if (!lock_user_struct(VERIFY_READ, target_fl, target_flock_addr, 1)) {
> +        return -TARGET_EFAULT;
> +    }
> +
> +    __get_user(l_type, &target_fl->l_type);
> +    fl->l_type = target_to_host_bitmask(l_type, flock_tbl);
> +    __get_user(fl->l_whence, &target_fl->l_whence);
> +    __get_user(fl->l_start, &target_fl->l_start);
> +    __get_user(fl->l_len, &target_fl->l_len);
> +    __get_user(fl->l_pid, &target_fl->l_pid);
> +    unlock_user_struct(target_fl, target_flock_addr, 0);
> +    return 0;
> +}
> +
> +static inline abi_long copy_to_user_eabi_flock64(abi_ulong target_flock_addr,
> +                                                 const struct flock64 *fl)
> +{
> +    struct target_eabi_flock64 *target_fl;
> +    short l_type;
> +
> +    if (!lock_user_struct(VERIFY_WRITE, target_fl, target_flock_addr, 0)) {
> +        return -TARGET_EFAULT;
> +    }
> +
> +    l_type = host_to_target_bitmask(fl->l_type, flock_tbl);
> +    __put_user(l_type, &target_fl->l_type);
> +    __put_user(fl->l_whence, &target_fl->l_whence);
> +    __put_user(fl->l_start, &target_fl->l_start);
> +    __put_user(fl->l_len, &target_fl->l_len);
> +    __put_user(fl->l_pid, &target_fl->l_pid);
> +    unlock_user_struct(target_fl, target_flock_addr, 1);
> +    return 0;
> +}
> +#endif
> +
> +static inline abi_long copy_from_user_flock64(struct flock64 *fl,
> +                                              abi_ulong target_flock_addr)
> +{
> +    struct target_flock64 *target_fl;
> +    short l_type;
> +
> +    if (!lock_user_struct(VERIFY_READ, target_fl, target_flock_addr, 1)) {
> +        return -TARGET_EFAULT;
> +    }
> +
> +    __get_user(l_type, &target_fl->l_type);
> +    fl->l_type = target_to_host_bitmask(l_type, flock_tbl);
> +    __get_user(fl->l_whence, &target_fl->l_whence);
> +    __get_user(fl->l_start, &target_fl->l_start);
> +    __get_user(fl->l_len, &target_fl->l_len);
> +    __get_user(fl->l_pid, &target_fl->l_pid);
> +    unlock_user_struct(target_fl, target_flock_addr, 0);
> +    return 0;
> +}
> +
> +static inline abi_long copy_to_user_flock64(abi_ulong target_flock_addr,
> +                                            const struct flock64 *fl)
> +{
> +    struct target_flock64 *target_fl;
> +    short l_type;
> +
> +    if (!lock_user_struct(VERIFY_WRITE, target_fl, target_flock_addr, 0)) {
> +        return -TARGET_EFAULT;
> +    }
> +
> +    l_type = host_to_target_bitmask(fl->l_type, flock_tbl);
> +    __put_user(l_type, &target_fl->l_type);
> +    __put_user(fl->l_whence, &target_fl->l_whence);
> +    __put_user(fl->l_start, &target_fl->l_start);
> +    __put_user(fl->l_len, &target_fl->l_len);
> +    __put_user(fl->l_pid, &target_fl->l_pid);
> +    unlock_user_struct(target_fl, target_flock_addr, 1);
> +    return 0;
> +}
> +
> +static abi_long do_fcntl(int fd, int cmd, abi_ulong arg)
> +{
>      struct flock64 fl64;
> -    struct target_flock64 *target_fl64;
>  #ifdef F_GETOWN_EX
>      struct f_owner_ex fox;
>      struct target_f_owner_ex *target_fox;
> @@ -4967,77 +5089,41 @@ static abi_long do_fcntl(int fd, int cmd, abi_ulong 
> arg)
>  
>      switch(cmd) {
>      case TARGET_F_GETLK:
> -        if (!lock_user_struct(VERIFY_READ, target_fl, arg, 1))
> +        if (copy_from_user_flock(&fl64, arg)) {
>              return -TARGET_EFAULT;

why do you ignore the exact value returned by copy_from_user_flock()?
You should return this value instead of guessing it.

> -        fl.l_type =
> -                  target_to_host_bitmask(tswap16(target_fl->l_type), 
> flock_tbl);
> -        fl.l_whence = tswap16(target_fl->l_whence);
> -        fl.l_start = tswapal(target_fl->l_start);
> -        fl.l_len = tswapal(target_fl->l_len);
> -        fl.l_pid = tswap32(target_fl->l_pid);
> -        unlock_user_struct(target_fl, arg, 0);
> -        ret = get_errno(fcntl(fd, host_cmd, &fl));
> +        }
> +        ret = get_errno(fcntl(fd, host_cmd, &fl64));
>          if (ret == 0) {
> -            if (!lock_user_struct(VERIFY_WRITE, target_fl, arg, 0))
> +            if (copy_to_user_flock(arg, &fl64)) {
>                  return -TARGET_EFAULT;
> -            target_fl->l_type =
> -                          host_to_target_bitmask(tswap16(fl.l_type), 
> flock_tbl);
> -            target_fl->l_whence = tswap16(fl.l_whence);
> -            target_fl->l_start = tswapal(fl.l_start);
> -            target_fl->l_len = tswapal(fl.l_len);
> -            target_fl->l_pid = tswap32(fl.l_pid);
> -            unlock_user_struct(target_fl, arg, 1);
> +            }
>          }
>          break;
>  
>      case TARGET_F_SETLK:
>      case TARGET_F_SETLKW:
> -        if (!lock_user_struct(VERIFY_READ, target_fl, arg, 1))
> +        if (copy_from_user_flock(&fl64, arg)) {
>              return -TARGET_EFAULT;

same as above

> -        fl.l_type =
> -                  target_to_host_bitmask(tswap16(target_fl->l_type), 
> flock_tbl);
> -        fl.l_whence = tswap16(target_fl->l_whence);
> -        fl.l_start = tswapal(target_fl->l_start);
> -        fl.l_len = tswapal(target_fl->l_len);
> -        fl.l_pid = tswap32(target_fl->l_pid);
> -        unlock_user_struct(target_fl, arg, 0);
> -        ret = get_errno(fcntl(fd, host_cmd, &fl));
> +        }
> +        ret = get_errno(fcntl(fd, host_cmd, &fl64));
>          break;
>  
>      case TARGET_F_GETLK64:
> -        if (!lock_user_struct(VERIFY_READ, target_fl64, arg, 1))
> +        if (copy_from_user_flock64(&fl64, arg)) {
>              return -TARGET_EFAULT;

same as above

> -        fl64.l_type =
> -           target_to_host_bitmask(tswap16(target_fl64->l_type), flock_tbl) 
> >> 1;

The ">> 1" disappears...

> -        fl64.l_whence = tswap16(target_fl64->l_whence);
> -        fl64.l_start = tswap64(target_fl64->l_start);
> -        fl64.l_len = tswap64(target_fl64->l_len);
> -        fl64.l_pid = tswap32(target_fl64->l_pid);
> -        unlock_user_struct(target_fl64, arg, 0);
> +        }
>          ret = get_errno(fcntl(fd, host_cmd, &fl64));
>          if (ret == 0) {
> -            if (!lock_user_struct(VERIFY_WRITE, target_fl64, arg, 0))
> +            if (copy_to_user_flock64(arg, &fl64)) {
>                  return -TARGET_EFAULT;

same as above

> -            target_fl64->l_type =
> -                   host_to_target_bitmask(tswap16(fl64.l_type), flock_tbl) 
> >> 1;
> -            target_fl64->l_whence = tswap16(fl64.l_whence);
> -            target_fl64->l_start = tswap64(fl64.l_start);
> -            target_fl64->l_len = tswap64(fl64.l_len);
> -            target_fl64->l_pid = tswap32(fl64.l_pid);
> -            unlock_user_struct(target_fl64, arg, 1);
> +            }
>          }
>          break;
>      case TARGET_F_SETLK64:
>      case TARGET_F_SETLKW64:
> -        if (!lock_user_struct(VERIFY_READ, target_fl64, arg, 1))
> +        if (copy_from_user_flock64(&fl64, arg)) {
>              return -TARGET_EFAULT;

same as above

> -        fl64.l_type =
> -           target_to_host_bitmask(tswap16(target_fl64->l_type), flock_tbl) 
> >> 1;
> -        fl64.l_whence = tswap16(target_fl64->l_whence);
> -        fl64.l_start = tswap64(target_fl64->l_start);
> -        fl64.l_len = tswap64(target_fl64->l_len);
> -        fl64.l_pid = tswap32(target_fl64->l_pid);
> -        unlock_user_struct(target_fl64, arg, 0);
> +        }
>          ret = get_errno(fcntl(fd, host_cmd, &fl64));
>          break;
>  
> @@ -9485,9 +9571,14 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
> arg1,
>      {
>       int cmd;
>       struct flock64 fl;
> -     struct target_flock64 *target_fl;
> +        from_flock64_fn *copyfrom = copy_from_user_flock64;
> +        to_flock64_fn *copyto = copy_to_user_flock64;
> +
>  #ifdef TARGET_ARM
> -     struct target_eabi_flock64 *target_efl;
> +        if (((CPUARMState *)cpu_env)->eabi) {
> +            copyfrom = copy_from_user_eabi_flock64;
> +            copyto = copy_to_user_eabi_flock64;
> +        }
>  #endif
>  
>       cmd = target_to_host_fcntl_cmd(arg2);
> @@ -9498,78 +9589,21 @@ abi_long do_syscall(void *cpu_env, int num, abi_long 
> arg1,
>  
>          switch(arg2) {
>          case TARGET_F_GETLK64:
> -#ifdef TARGET_ARM
> -            if (((CPUARMState *)cpu_env)->eabi) {
> -                if (!lock_user_struct(VERIFY_READ, target_efl, arg3, 1)) 
> -                    goto efault;
> -                fl.l_type = tswap16(target_efl->l_type);
> -                fl.l_whence = tswap16(target_efl->l_whence);
> -                fl.l_start = tswap64(target_efl->l_start);
> -                fl.l_len = tswap64(target_efl->l_len);
> -                fl.l_pid = tswap32(target_efl->l_pid);
> -                unlock_user_struct(target_efl, arg3, 0);
> -            } else
> -#endif
> -            {
> -                if (!lock_user_struct(VERIFY_READ, target_fl, arg3, 1)) 
> -                    goto efault;
> -                fl.l_type = tswap16(target_fl->l_type);
> -                fl.l_whence = tswap16(target_fl->l_whence);
> -                fl.l_start = tswap64(target_fl->l_start);
> -                fl.l_len = tswap64(target_fl->l_len);
> -                fl.l_pid = tswap32(target_fl->l_pid);
> -                unlock_user_struct(target_fl, arg3, 0);
> +            if (copyfrom(&fl, arg3)) {
> +                goto efault;
>              }
>              ret = get_errno(fcntl(arg1, cmd, &fl));
>           if (ret == 0) {
> -#ifdef TARGET_ARM
> -                if (((CPUARMState *)cpu_env)->eabi) {
> -                    if (!lock_user_struct(VERIFY_WRITE, target_efl, arg3, 
> 0)) 
> -                        goto efault;
> -                    target_efl->l_type = tswap16(fl.l_type);
> -                    target_efl->l_whence = tswap16(fl.l_whence);
> -                    target_efl->l_start = tswap64(fl.l_start);
> -                    target_efl->l_len = tswap64(fl.l_len);
> -                    target_efl->l_pid = tswap32(fl.l_pid);
> -                    unlock_user_struct(target_efl, arg3, 1);
> -                } else
> -#endif
> -                {
> -                    if (!lock_user_struct(VERIFY_WRITE, target_fl, arg3, 0)) 
> -                        goto efault;
> -                    target_fl->l_type = tswap16(fl.l_type);
> -                    target_fl->l_whence = tswap16(fl.l_whence);
> -                    target_fl->l_start = tswap64(fl.l_start);
> -                    target_fl->l_len = tswap64(fl.l_len);
> -                    target_fl->l_pid = tswap32(fl.l_pid);
> -                    unlock_user_struct(target_fl, arg3, 1);
> +                if (copyto(arg3, &fl)) {
> +                    goto efault;
>                  }
>           }
>           break;
>  
>          case TARGET_F_SETLK64:
>          case TARGET_F_SETLKW64:
> -#ifdef TARGET_ARM
> -            if (((CPUARMState *)cpu_env)->eabi) {
> -                if (!lock_user_struct(VERIFY_READ, target_efl, arg3, 1)) 
> -                    goto efault;
> -                fl.l_type = tswap16(target_efl->l_type);
> -                fl.l_whence = tswap16(target_efl->l_whence);
> -                fl.l_start = tswap64(target_efl->l_start);
> -                fl.l_len = tswap64(target_efl->l_len);
> -                fl.l_pid = tswap32(target_efl->l_pid);
> -                unlock_user_struct(target_efl, arg3, 0);
> -            } else
> -#endif
> -            {
> -                if (!lock_user_struct(VERIFY_READ, target_fl, arg3, 1)) 
> -                    goto efault;
> -                fl.l_type = tswap16(target_fl->l_type);
> -                fl.l_whence = tswap16(target_fl->l_whence);
> -                fl.l_start = tswap64(target_fl->l_start);
> -                fl.l_len = tswap64(target_fl->l_len);
> -                fl.l_pid = tswap32(target_fl->l_pid);
> -                unlock_user_struct(target_fl, arg3, 0);
> +            if (copyfrom(&fl, arg3)) {
> +                goto efault;
>              }
>              ret = get_errno(fcntl(arg1, cmd, &fl));
>           break;
>