Fix STM32F2XX USART data register readout

[PATCH] Fix STM32F2XX USART data register readout

Posted by Olivier Hériveaux 2 years, 5 months ago

Fix issue where the data register may be overwritten by next character
reception before being read and returned.

Signed-off-by: Olivier Hériveaux <olivier.heriveaux@ledger.fr>
---
 hw/char/stm32f2xx_usart.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/hw/char/stm32f2xx_usart.c b/hw/char/stm32f2xx_usart.c
index 8df0832424..fde67f4f03 100644
--- a/hw/char/stm32f2xx_usart.c
+++ b/hw/char/stm32f2xx_usart.c
@@ -103,10 +103,11 @@ static uint64_t stm32f2xx_usart_read(void *opaque, hwaddr addr,
         return retvalue;
     case USART_DR:
         DB_PRINT("Value: 0x%" PRIx32 ", %c\n", s->usart_dr, (char) s->usart_dr);
+        retvalue = s->usart_dr & 0x3FF;
         s->usart_sr &= ~USART_SR_RXNE;
         qemu_chr_fe_accept_input(&s->chr);
         qemu_set_irq(s->irq, 0);
-        return s->usart_dr & 0x3FF;
+        return retvalue;
     case USART_BRR:
         return s->usart_brr;
     case USART_CR1:
-- 
2.17.1


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Re: [PATCH] Fix STM32F2XX USART data register readout

Posted by Peter Maydell 2 years, 5 months ago

On Sun, 28 Nov 2021 at 12:07, Olivier Hériveaux
<olivier.heriveaux@ledger.fr> wrote:
>
> Fix issue where the data register may be overwritten by next character
> reception before being read and returned.
>
> Signed-off-by: Olivier Hériveaux <olivier.heriveaux@ledger.fr>
> ---
>  hw/char/stm32f2xx_usart.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/hw/char/stm32f2xx_usart.c b/hw/char/stm32f2xx_usart.c
> index 8df0832424..fde67f4f03 100644
> --- a/hw/char/stm32f2xx_usart.c
> +++ b/hw/char/stm32f2xx_usart.c
> @@ -103,10 +103,11 @@ static uint64_t stm32f2xx_usart_read(void *opaque, hwaddr addr,
>          return retvalue;
>      case USART_DR:
>          DB_PRINT("Value: 0x%" PRIx32 ", %c\n", s->usart_dr, (char) s->usart_dr);
> +        retvalue = s->usart_dr & 0x3FF;
>          s->usart_sr &= ~USART_SR_RXNE;
>          qemu_chr_fe_accept_input(&s->chr);
>          qemu_set_irq(s->irq, 0);
> -        return s->usart_dr & 0x3FF;
> +        return retvalue;
>      case USART_BRR:
>          return s->usart_brr;
>      case USART_CR1:
> --
> 2.17.1

The bug happens because qemu_chr_fe_accept_input() can cause
stm32f2xx_usart_receive() to be called, right ?

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

I'll put this in my list of patches to take via target-arm.next for the
7.0 release.

thanks
-- PMM

Re: [PATCH] Fix STM32F2XX USART data register readout

Posted by Olivier Heriveaux 2 years, 5 months ago

If I understand correctly (I'm not a QEmu internals expert), yes this is
what happens.
Maybe stm32f2xx_usart_can_receive() is also called but since the
USART_SR_RXNE flag is reset before the USART_DR is read, it does not
prevent reading the next character.

Best regards,
Olivier Hériveaux

Le lun. 29 nov. 2021 à 11:46, Peter Maydell <peter.maydell@linaro.org> a
écrit :

> On Sun, 28 Nov 2021 at 12:07, Olivier Hériveaux
> <olivier.heriveaux@ledger.fr> wrote:
> >
> > Fix issue where the data register may be overwritten by next character
> > reception before being read and returned.
> >
> > Signed-off-by: Olivier Hériveaux <olivier.heriveaux@ledger.fr>
> > ---
> >  hw/char/stm32f2xx_usart.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/char/stm32f2xx_usart.c b/hw/char/stm32f2xx_usart.c
> > index 8df0832424..fde67f4f03 100644
> > --- a/hw/char/stm32f2xx_usart.c
> > +++ b/hw/char/stm32f2xx_usart.c
> > @@ -103,10 +103,11 @@ static uint64_t stm32f2xx_usart_read(void *opaque,
> hwaddr addr,
> >          return retvalue;
> >      case USART_DR:
> >          DB_PRINT("Value: 0x%" PRIx32 ", %c\n", s->usart_dr, (char)
> s->usart_dr);
> > +        retvalue = s->usart_dr & 0x3FF;
> >          s->usart_sr &= ~USART_SR_RXNE;
> >          qemu_chr_fe_accept_input(&s->chr);
> >          qemu_set_irq(s->irq, 0);
> > -        return s->usart_dr & 0x3FF;
> > +        return retvalue;
> >      case USART_BRR:
> >          return s->usart_brr;
> >      case USART_CR1:
> > --
> > 2.17.1
>
> The bug happens because qemu_chr_fe_accept_input() can cause
> stm32f2xx_usart_receive() to be called, right ?
>
> Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
>
> I'll put this in my list of patches to take via target-arm.next for the
> 7.0 release.
>
> thanks
> -- PMM
>

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Partial or total 
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Re: [PATCH] Fix STM32F2XX USART data register readout

Posted by Alistair Francis 2 years, 5 months ago

On Mon, Nov 29, 2021 at 12:46 AM Olivier Hériveaux
<olivier.heriveaux@ledger.fr> wrote:
>
> Fix issue where the data register may be overwritten by next character
> reception before being read and returned.
>
> Signed-off-by: Olivier Hériveaux <olivier.heriveaux@ledger.fr>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

> ---
>  hw/char/stm32f2xx_usart.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/hw/char/stm32f2xx_usart.c b/hw/char/stm32f2xx_usart.c
> index 8df0832424..fde67f4f03 100644
> --- a/hw/char/stm32f2xx_usart.c
> +++ b/hw/char/stm32f2xx_usart.c
> @@ -103,10 +103,11 @@ static uint64_t stm32f2xx_usart_read(void *opaque, hwaddr addr,
>          return retvalue;
>      case USART_DR:
>          DB_PRINT("Value: 0x%" PRIx32 ", %c\n", s->usart_dr, (char) s->usart_dr);
> +        retvalue = s->usart_dr & 0x3FF;
>          s->usart_sr &= ~USART_SR_RXNE;
>          qemu_chr_fe_accept_input(&s->chr);
>          qemu_set_irq(s->irq, 0);
> -        return s->usart_dr & 0x3FF;
> +        return retvalue;
>      case USART_BRR:
>          return s->usart_brr;
>      case USART_CR1:
> --
> 2.17.1
>
>
> --
>
> Les informations contenues dans ce message électronique ainsi que celles
> contenues dans les documents attachés sont strictement confidentielles et
> sont destinées à l'usage exclusif du (des) destinataire(s) nommé(s).
> Toute
> divulgation, distribution ou reproduction, même partielle, en est
> strictement interdite sauf autorisation écrite et expresse de l’émetteur.
> Si vous recevez ce message par erreur, veuillez le notifier immédiatement à
> son émetteur par retour, et le détruire ainsi que tous les documents qui y
> sont attachés.
>
>
> The information contained in this email and in any
> document enclosed is strictly confidential and is intended solely for the
> use of the individual or entity to which it is addressed.
> Partial or total
> disclosure, distribution or reproduction of its contents is strictly
> prohibited unless expressly approved in writing by the sender.
> If you have
> received this communication in error, please notify us immediately by
> responding to this email, and then delete the message and its attached
> files from your system.
>
>