Re: [PATCH] linux-user: Use signed lengths in uaccess.c

[Laurent Vivier <laurent@vivier.eu>]

Le 15/03/2021 à 21:40, Richard Henderson a écrit :
> Partially revert 09f679b62dff, but only for the length arguments.
> Instead of reverting to long, use ssize_t.  Reinstate the > 0 check
> in unlock_user.
> 
> Fixes: 09f679b62dff
> Reported-by: Coverity (CID 1446711)
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  linux-user/qemu.h    | 15 +++++++++------
>  linux-user/uaccess.c | 12 ++++++------
>  2 files changed, 15 insertions(+), 12 deletions(-)
> 
> diff --git a/linux-user/qemu.h b/linux-user/qemu.h
> index 52c981710b..74e06e7121 100644
> --- a/linux-user/qemu.h
> +++ b/linux-user/qemu.h
> @@ -627,8 +627,8 @@ static inline bool access_ok(CPUState *cpu, int type,
>   * buffers between the target and host.  These internally perform
>   * locking/unlocking of the memory.
>   */
> -int copy_from_user(void *hptr, abi_ulong gaddr, size_t len);
> -int copy_to_user(abi_ulong gaddr, void *hptr, size_t len);
> +int copy_from_user(void *hptr, abi_ulong gaddr, ssize_t len);
> +int copy_to_user(abi_ulong gaddr, void *hptr, ssize_t len);
>  
>  /* Functions for accessing guest memory.  The tget and tput functions
>     read/write single values, byteswapping as necessary.  The lock_user function
> @@ -638,16 +638,19 @@ int copy_to_user(abi_ulong gaddr, void *hptr, size_t len);
>  
>  /* Lock an area of guest memory into the host.  If copy is true then the
>     host area will have the same contents as the guest.  */
> -void *lock_user(int type, abi_ulong guest_addr, size_t len, bool copy);
> +void *lock_user(int type, abi_ulong guest_addr, ssize_t len, bool copy);
>  
>  /* Unlock an area of guest memory.  The first LEN bytes must be
>     flushed back to guest memory. host_ptr = NULL is explicitly
>     allowed and does nothing. */
>  #ifndef DEBUG_REMAP
> -static inline void unlock_user(void *host_ptr, abi_ulong guest_addr, size_t len)
> -{ }
> +static inline void unlock_user(void *host_ptr, abi_ulong guest_addr,
> +                               ssize_t len)
> +{
> +    /* no-op */
> +}
>  #else
> -void unlock_user(void *host_ptr, abi_ulong guest_addr, long len);
> +void unlock_user(void *host_ptr, abi_ulong guest_addr, ssize_t len);
>  #endif
>  
>  /* Return the length of a string in target memory or -TARGET_EFAULT if
> diff --git a/linux-user/uaccess.c b/linux-user/uaccess.c
> index c696913016..82b833b8f1 100644
> --- a/linux-user/uaccess.c
> +++ b/linux-user/uaccess.c
> @@ -4,7 +4,7 @@
>  
>  #include "qemu.h"
>  
> -void *lock_user(int type, abi_ulong guest_addr, size_t len, bool copy)
> +void *lock_user(int type, abi_ulong guest_addr, ssize_t len, bool copy)
>  {
>      void *host_addr;
>  
> @@ -24,7 +24,7 @@ void *lock_user(int type, abi_ulong guest_addr, size_t len, bool copy)
>  }
>  
>  #ifdef DEBUG_REMAP
> -void unlock_user(void *host_ptr, abi_ulong guest_addr, size_t len);
> +void unlock_user(void *host_ptr, abi_ulong guest_addr, ssize_t len);

The semicolon has been added by 687ca797893c ("linux-user: Move lock_user et al out of line")
perhaps it's time to remove it?

Reviewed-by: Laurent Vivier <laurent@vivier.eu>