[Qemu-devel] [PATCH] linux-user: Handle negative values in timespec conversion

[Peter Maydell <peter.maydell@linaro.org>]

In a struct timespec, both fields are signed longs. Converting
them from guest to host with code like
    host_ts->tv_sec = tswapal(target_ts->tv_sec);
mishandles negative values if the guest has 32-bit longs and
the host has 64-bit longs because tswapal()'s return type is
abi_ulong: the assignment will zero-extend into the host long
type rather than sign-extending it.

Make the conversion routines use __get_user() and __set_user()
instead: this automatically picks up the signedness of the
field type and does the correct kind of sign or zero extension.
It also handles the possibility that the target struct is not
sufficiently aligned for the host's requirements.

In particular, this fixes a hang when running the Linux Test Project
mq_timedsend01 and mq_timedreceive01 tests: one of the test cases
sets the timeout to -1 and expects an EINVAL failure, but we were
setting a very long timeout instead.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
I suspect many of the uses of tswap*() in syscall.c should really
be using the get/put user functions instead, but don't propose
to audit them all now.
---
 linux-user/syscall.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 032d338..077175f 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -5137,8 +5137,8 @@ static inline abi_long target_to_host_timespec(struct timespec *host_ts,
 
     if (!lock_user_struct(VERIFY_READ, target_ts, target_addr, 1))
         return -TARGET_EFAULT;
-    host_ts->tv_sec = tswapal(target_ts->tv_sec);
-    host_ts->tv_nsec = tswapal(target_ts->tv_nsec);
+    __get_user(host_ts->tv_sec, &target_ts->tv_sec);
+    __get_user(host_ts->tv_nsec, &target_ts->tv_nsec);
     unlock_user_struct(target_ts, target_addr, 0);
     return 0;
 }
@@ -5150,8 +5150,8 @@ static inline abi_long host_to_target_timespec(abi_ulong target_addr,
 
     if (!lock_user_struct(VERIFY_WRITE, target_ts, target_addr, 0))
         return -TARGET_EFAULT;
-    target_ts->tv_sec = tswapal(host_ts->tv_sec);
-    target_ts->tv_nsec = tswapal(host_ts->tv_nsec);
+    __put_user(host_ts->tv_sec, &target_ts->tv_sec);
+    __put_user(host_ts->tv_nsec, &target_ts->tv_nsec);
     unlock_user_struct(target_ts, target_addr, 1);
     return 0;
 }
-- 
1.9.1