linux-user: Use signed lengths in uaccess.c

Partially revert 09f679b62d, but only for the length arguments.
Instead of reverting to long, use ssize_t.  Reinstate the > 0 check
in unlock_user.

Fixes: 09f679b62d
Reported-by: Coverity (CID 1446711)
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20210315204004.2025219-1-richard.henderson@linaro.org>
[lv: remove superfluous semicolon]
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

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

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)
 {
     void *host_ptr_conv;
 
@@ -35,7 +35,7 @@ void unlock_user(void *host_ptr, abi_ulong guest_addr, size_t len);
     if (host_ptr == host_ptr_conv) {
         return;
     }
-    if (len != 0) {
+    if (len > 0) {
         memcpy(host_ptr_conv, host_ptr, len);
     }
     g_free(host_ptr);
@@ -48,14 +48,14 @@ void *lock_user_string(abi_ulong guest_addr)
     if (len < 0) {
         return NULL;
     }
-    return lock_user(VERIFY_READ, guest_addr, (size_t)len + 1, 1);
+    return lock_user(VERIFY_READ, guest_addr, len + 1, 1);
 }
 
 /* copy_from_user() and copy_to_user() are usually used to copy data
  * 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_from_user(void *hptr, abi_ulong gaddr, ssize_t len)
 {
     int ret = 0;
     void *ghptr = lock_user(VERIFY_READ, gaddr, len, 1);
@@ -69,7 +69,7 @@ int copy_from_user(void *hptr, abi_ulong gaddr, size_t len)
     return ret;
 }
 
-int copy_to_user(abi_ulong gaddr, void *hptr, size_t len)
+int copy_to_user(abi_ulong gaddr, void *hptr, ssize_t len)
 {
     int ret = 0;
     void *ghptr = lock_user(VERIFY_WRITE, gaddr, len, 0);