[PATCH v4 31/53] semihosting: Bound length for semihost_sys_{read, write}

[Richard Henderson <richard.henderson@linaro.org>]

Fixes a minor bug in which a 64-bit guest on a 32-bit host could
truncate the length.  This would only ever cause a problem if
there were no bits set in the low 32, so that it truncates to 0.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 semihosting/syscalls.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/semihosting/syscalls.c b/semihosting/syscalls.c
index 5cb12d6adc..eefbae74f1 100644
--- a/semihosting/syscalls.c
+++ b/semihosting/syscalls.c
@@ -283,6 +283,14 @@ void semihost_sys_close(CPUState *cs, gdb_syscall_complete_cb complete, int fd)
 void semihost_sys_read_gf(CPUState *cs, gdb_syscall_complete_cb complete,
                           GuestFD *gf, target_ulong buf, target_ulong len)
 {
+    /*
+     * Bound length for 64-bit guests on 32-bit hosts, not overlowing ssize_t.
+     * Note the Linux kernel does this with MAX_RW_COUNT, so it's not a bad
+     * idea to do this unconditionally.
+     */
+    if (len > INT32_MAX) {
+        len = INT32_MAX;
+    }
     switch (gf->type) {
     case GuestFDGDB:
         gdb_read(cs, complete, gf, buf, len);
@@ -313,6 +321,14 @@ void semihost_sys_read(CPUState *cs, gdb_syscall_complete_cb complete,
 void semihost_sys_write_gf(CPUState *cs, gdb_syscall_complete_cb complete,
                            GuestFD *gf, target_ulong buf, target_ulong len)
 {
+    /*
+     * Bound length for 64-bit guests on 32-bit hosts, not overlowing ssize_t.
+     * Note the Linux kernel does this with MAX_RW_COUNT, so it's not a bad
+     * idea to do this unconditionally.
+     */
+    if (len > INT32_MAX) {
+        len = INT32_MAX;
+    }
     switch (gf->type) {
     case GuestFDGDB:
         gdb_write(cs, complete, gf, buf, len);
-- 
2.34.1