[PATCH 0/2] hw/timer/renesas_tmr: Fix use of uninitialized data

[PATCH 0/2] hw/timer/renesas_tmr: Fix use of uninitialized data

[Peter Maydell]

This patchseries fixes a use-of-uninitialized-data spotted by Coverity
(CID 1429976).

Patch 1 just tweaks some constant names for values of the TCCR.CSS
register field, since patch 2 needs to add some more defines
for the other possible values of the field.

Patch 2 is the bugfix proper; the use-uninitialized happens if the
guest programs TCCR.CSS to values which are either prohibited in
the h/w datasheet, or valid but corresponding to behaviour not
currently implemented by QEMU. (Yes, I could have added LOG_UNIMP
and/or LOG_GUEST_ERROR when the TCCR is written by the guest; it
didn't really seem worth the effort to me.)

thanks
-- PMM

Peter Maydell (2):
  hw/timer/renesas_tmr: Prefix constants for CSS values with CSS_
  hw/timer/renesas_tmr: Fix use of uninitialized data in read_tcnt()

 hw/timer/renesas_tmr.c | 33 ++++++++++++++++++++++-----------
 1 file changed, 22 insertions(+), 11 deletions(-)

-- 
2.20.1

[PATCH 1/2] hw/timer/renesas_tmr: Prefix constants for CSS values with CSS_

[Peter Maydell]

The #defines INTERNAL and CASCADING represent different possible
values for the TCCR.CSS register field; prefix them with CSS_ to make
this more obvious, before we add more defines to represent the
other possible values of the field in the next commit.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 hw/timer/renesas_tmr.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/hw/timer/renesas_tmr.c b/hw/timer/renesas_tmr.c
index e03a8155b2b..22260aaaba5 100644
--- a/hw/timer/renesas_tmr.c
+++ b/hw/timer/renesas_tmr.c
@@ -46,8 +46,8 @@ REG8(TCCR, 10)
   FIELD(TCCR, CSS,   3, 2)
   FIELD(TCCR, TMRIS, 7, 1)
 
-#define INTERNAL  0x01
-#define CASCADING 0x03
+#define CSS_INTERNAL  0x01
+#define CSS_CASCADING 0x03
 #define CCLR_A    0x01
 #define CCLR_B    0x02
 
@@ -72,7 +72,7 @@ static void update_events(RTMRState *tmr, int ch)
         /* event not happened */
         return ;
     }
-    if (FIELD_EX8(tmr->tccr[0], TCCR, CSS) == CASCADING) {
+    if (FIELD_EX8(tmr->tccr[0], TCCR, CSS) == CSS_CASCADING) {
         /* cascading mode */
         if (ch == 1) {
             tmr->next[ch] = none;
@@ -130,7 +130,7 @@ static uint16_t read_tcnt(RTMRState *tmr, unsigned size, int ch)
     if (delta > 0) {
         tmr->tick = now;
 
-        if (FIELD_EX8(tmr->tccr[1], TCCR, CSS) == INTERNAL) {
+        if (FIELD_EX8(tmr->tccr[1], TCCR, CSS) == CSS_INTERNAL) {
             /* timer1 count update */
             elapsed = elapsed_time(tmr, 1, delta);
             if (elapsed >= 0x100) {
@@ -139,11 +139,11 @@ static uint16_t read_tcnt(RTMRState *tmr, unsigned size, int ch)
             tcnt[1] = tmr->tcnt[1] + (elapsed & 0xff);
         }
         switch (FIELD_EX8(tmr->tccr[0], TCCR, CSS)) {
-        case INTERNAL:
+        case CSS_INTERNAL:
             elapsed = elapsed_time(tmr, 0, delta);
             tcnt[0] = tmr->tcnt[0] + elapsed;
             break;
-        case CASCADING:
+        case CSS_CASCADING:
             if (ovf > 0) {
                 tcnt[0] = tmr->tcnt[0] + ovf;
             }
@@ -330,7 +330,7 @@ static uint16_t issue_event(RTMRState *tmr, int ch, int sz,
                 qemu_irq_pulse(tmr->cmia[ch]);
             }
             if (sz == 8 && ch == 0 &&
-                FIELD_EX8(tmr->tccr[1], TCCR, CSS) == CASCADING) {
+                FIELD_EX8(tmr->tccr[1], TCCR, CSS) == CSS_CASCADING) {
                 tmr->tcnt[1]++;
                 timer_events(tmr, 1);
             }
@@ -362,7 +362,7 @@ static void timer_events(RTMRState *tmr, int ch)
     uint16_t tcnt;
 
     tmr->tcnt[ch] = read_tcnt(tmr, 1, ch);
-    if (FIELD_EX8(tmr->tccr[0], TCCR, CSS) != CASCADING) {
+    if (FIELD_EX8(tmr->tccr[0], TCCR, CSS) != CSS_CASCADING) {
         tmr->tcnt[ch] = issue_event(tmr, ch, 8,
                                     tmr->tcnt[ch],
                                     tmr->tcora[ch],
-- 
2.20.1

[PATCH 2/2] hw/timer/renesas_tmr: Fix use of uninitialized data in read_tcnt()

[Peter Maydell]

The read_tcnt() function calculates the TCNT register values for the
two channels of the timer module; it sets these up in the local
tcnt[] array, and eventually returns either one or both of them,
depending on whether the access is 8 or 16 bits.  However, not all of
the code paths through this function set both elements of this array:
if the guest has programmed the TCCR.CSS register fields to values
which are either documented as not to be used or which QEMU does not
implement, then the function will return uninitialized data.  (This
was spotted by Coverity.)

Add the missing CSS cases to this code, so that we return a
consistent value instead of uninitialized data, and so the code
structure indicates what's happening.

Fixes: CID 1429976
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 hw/timer/renesas_tmr.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/hw/timer/renesas_tmr.c b/hw/timer/renesas_tmr.c
index 22260aaaba5..eed39917fec 100644
--- a/hw/timer/renesas_tmr.c
+++ b/hw/timer/renesas_tmr.c
@@ -46,7 +46,9 @@ REG8(TCCR, 10)
   FIELD(TCCR, CSS,   3, 2)
   FIELD(TCCR, TMRIS, 7, 1)
 
+#define CSS_EXTERNAL  0x00
 #define CSS_INTERNAL  0x01
+#define CSS_INVALID   0x02
 #define CSS_CASCADING 0x03
 #define CCLR_A    0x01
 #define CCLR_B    0x02
@@ -130,13 +132,20 @@ static uint16_t read_tcnt(RTMRState *tmr, unsigned size, int ch)
     if (delta > 0) {
         tmr->tick = now;
 
-        if (FIELD_EX8(tmr->tccr[1], TCCR, CSS) == CSS_INTERNAL) {
+        switch (FIELD_EX8(tmr->tccr[1], TCCR, CSS)) {
+        case CSS_INTERNAL:
             /* timer1 count update */
             elapsed = elapsed_time(tmr, 1, delta);
             if (elapsed >= 0x100) {
                 ovf = elapsed >> 8;
             }
             tcnt[1] = tmr->tcnt[1] + (elapsed & 0xff);
+            break;
+        case CSS_INVALID: /* guest error to have set this */
+        case CSS_EXTERNAL: /* QEMU doesn't implement these */
+        case CSS_CASCADING:
+            tcnt[1] = tmr->tcnt[1];
+            break;
         }
         switch (FIELD_EX8(tmr->tccr[0], TCCR, CSS)) {
         case CSS_INTERNAL:
@@ -144,9 +153,11 @@ static uint16_t read_tcnt(RTMRState *tmr, unsigned size, int ch)
             tcnt[0] = tmr->tcnt[0] + elapsed;
             break;
         case CSS_CASCADING:
-            if (ovf > 0) {
-                tcnt[0] = tmr->tcnt[0] + ovf;
-            }
+            tcnt[0] = tmr->tcnt[0] + ovf;
+            break;
+        case CSS_INVALID: /* guest error to have set this */
+        case CSS_EXTERNAL: /* QEMU doesn't implement this */
+            tcnt[0] = tmr->tcnt[0];
             break;
         }
     } else {
-- 
2.20.1

Re: [PATCH 1/2] hw/timer/renesas_tmr: Prefix constants for CSS values with CSS_

[Philippe Mathieu-Daudé]

On 2/19/21 11:32 PM, Peter Maydell wrote:
> The #defines INTERNAL and CASCADING represent different possible
> values for the TCCR.CSS register field; prefix them with CSS_ to make
> this more obvious, before we add more defines to represent the
> other possible values of the field in the next commit.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  hw/timer/renesas_tmr.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

Re: [PATCH 2/2] hw/timer/renesas_tmr: Fix use of uninitialized data in read_tcnt()

[Philippe Mathieu-Daudé]

On 2/19/21 11:32 PM, Peter Maydell wrote:
> The read_tcnt() function calculates the TCNT register values for the
> two channels of the timer module; it sets these up in the local
> tcnt[] array, and eventually returns either one or both of them,
> depending on whether the access is 8 or 16 bits.  However, not all of
> the code paths through this function set both elements of this array:
> if the guest has programmed the TCCR.CSS register fields to values
> which are either documented as not to be used or which QEMU does not
> implement, then the function will return uninitialized data.  (This
> was spotted by Coverity.)
> 
> Add the missing CSS cases to this code, so that we return a
> consistent value instead of uninitialized data, and so the code
> structure indicates what's happening.
> 
> Fixes: CID 1429976
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  hw/timer/renesas_tmr.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/timer/renesas_tmr.c b/hw/timer/renesas_tmr.c
> index 22260aaaba5..eed39917fec 100644
> --- a/hw/timer/renesas_tmr.c
> +++ b/hw/timer/renesas_tmr.c
> @@ -46,7 +46,9 @@ REG8(TCCR, 10)
>    FIELD(TCCR, CSS,   3, 2)
>    FIELD(TCCR, TMRIS, 7, 1)
>  
> +#define CSS_EXTERNAL  0x00
>  #define CSS_INTERNAL  0x01
> +#define CSS_INVALID   0x02
>  #define CSS_CASCADING 0x03
>  #define CCLR_A    0x01
>  #define CCLR_B    0x02
> @@ -130,13 +132,20 @@ static uint16_t read_tcnt(RTMRState *tmr, unsigned size, int ch)
>      if (delta > 0) {
>          tmr->tick = now;
>  
> -        if (FIELD_EX8(tmr->tccr[1], TCCR, CSS) == CSS_INTERNAL) {
> +        switch (FIELD_EX8(tmr->tccr[1], TCCR, CSS)) {
> +        case CSS_INTERNAL:
>              /* timer1 count update */
>              elapsed = elapsed_time(tmr, 1, delta);
>              if (elapsed >= 0x100) {
>                  ovf = elapsed >> 8;
>              }
>              tcnt[1] = tmr->tcnt[1] + (elapsed & 0xff);
> +            break;
> +        case CSS_INVALID: /* guest error to have set this */
> +        case CSS_EXTERNAL: /* QEMU doesn't implement these */
> +        case CSS_CASCADING:
> +            tcnt[1] = tmr->tcnt[1];
> +            break;
>          }
>          switch (FIELD_EX8(tmr->tccr[0], TCCR, CSS)) {
>          case CSS_INTERNAL:
> @@ -144,9 +153,11 @@ static uint16_t read_tcnt(RTMRState *tmr, unsigned size, int ch)
>              tcnt[0] = tmr->tcnt[0] + elapsed;
>              break;
>          case CSS_CASCADING:
> -            if (ovf > 0) {
> -                tcnt[0] = tmr->tcnt[0] + ovf;
> -            }
> +            tcnt[0] = tmr->tcnt[0] + ovf;
> +            break;
> +        case CSS_INVALID: /* guest error to have set this */
> +        case CSS_EXTERNAL: /* QEMU doesn't implement this */
> +            tcnt[0] = tmr->tcnt[0];
>              break;
>          }

Elegant nice fix :)

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>