[PULL 05/15] hw/audio/hda-codec: fix multiplication overflow

[Michael S. Tsirkin]

From: Volker Rümelin <vr_qemu@t-online.de>

After a relatively short time, there is an multiplication overflow
when multiplying (now - buft_start) with hda_bytes_per_second().
While the uptime now - buft_start only overflows after 2**63 ns
= 292.27 years, this happens hda_bytes_per_second() times faster
with the multiplication. At 44100 samples/s * 2 channels
* 2 bytes/channel = 176400 bytes/s that is 14.52 hours. After the
multiplication overflow the affected audio stream stalls.

Replace the multiplication and following division with muldiv64()
to prevent a multiplication overflow.

Fixes: 280c1e1cdb ("audio/hda: create millisecond timers that handle IO")
Reported-by: M_O_Bz <m_o_bz@163.com>
Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Message-Id: <20231105172552.8405-1-vr_qemu@t-online.de>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/audio/hda-codec.c | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/hw/audio/hda-codec.c b/hw/audio/hda-codec.c
index b9ad1f4c39..f756e419bb 100644
--- a/hw/audio/hda-codec.c
+++ b/hw/audio/hda-codec.c
@@ -22,6 +22,7 @@
 #include "hw/qdev-properties.h"
 #include "intel-hda.h"
 #include "migration/vmstate.h"
+#include "qemu/host-utils.h"
 #include "qemu/module.h"
 #include "intel-hda-defs.h"
 #include "audio/audio.h"
@@ -189,9 +190,9 @@ struct HDAAudioState {
     bool     use_timer;
 };
 
-static inline int64_t hda_bytes_per_second(HDAAudioStream *st)
+static inline uint32_t hda_bytes_per_second(HDAAudioStream *st)
 {
-    return 2LL * st->as.nchannels * st->as.freq;
+    return 2 * (uint32_t)st->as.nchannels * (uint32_t)st->as.freq;
 }
 
 static inline void hda_timer_sync_adjust(HDAAudioStream *st, int64_t 
target_pos)
@@ -222,12 +223,18 @@ static void hda_audio_input_timer(void *opaque)
 
     int64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 
-    int64_t buft_start = st->buft_start;
+    int64_t uptime = now - st->buft_start;
     int64_t wpos = st->wpos;
     int64_t rpos = st->rpos;
+    int64_t wanted_rpos;
 
-    int64_t wanted_rpos = hda_bytes_per_second(st) * (now - buft_start)
-                          / NANOSECONDS_PER_SECOND;
+    if (uptime <= 0) {
+        /* wanted_rpos <= 0 */
+        goto out_timer;
+    }
+
+    wanted_rpos = muldiv64(uptime, hda_bytes_per_second(st),
+                           NANOSECONDS_PER_SECOND);
     wanted_rpos &= -4; /* IMPORTANT! clip to frames */
 
     if (wanted_rpos <= rpos) {
@@ -286,12 +293,18 @@ static void hda_audio_output_timer(void *opaque)
 
     int64_t now = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
 
-    int64_t buft_start = st->buft_start;
+    int64_t uptime = now - st->buft_start;
     int64_t wpos = st->wpos;
     int64_t rpos = st->rpos;
+    int64_t wanted_wpos;
 
-    int64_t wanted_wpos = hda_bytes_per_second(st) * (now - buft_start)
-                          / NANOSECONDS_PER_SECOND;
+    if (uptime <= 0) {
+        /* wanted_wpos <= 0 */
+        goto out_timer;
+    }
+
+    wanted_wpos = muldiv64(uptime, hda_bytes_per_second(st),
+                           NANOSECONDS_PER_SECOND);
     wanted_wpos &= -4; /* IMPORTANT! clip to frames */
 
     if (wanted_wpos <= wpos) {
-- 
MST