| Message ID | 20210219223241.16344-3-peter.maydell@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | hw/timer/renesas_tmr: Fix use of uninitialized data | expand |
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>
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 {
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(-) -- 2.20.1