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[PATCH v2] ati-vga: check mm_index before recursive call

P J P posted 1 patch 5 years, 8 months ago
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git fetch https://github.com/patchew-project/qemu tags/patchew/20200603185522.1173354-1-ppandit@redhat.com
hw/display/ati.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
[PATCH v2] ati-vga: check mm_index before recursive call
Posted by P J P 5 years, 8 months ago 
From: Prasad J Pandit <pjp@fedoraproject.org>

While accessing VGA registers via ati_mm_read/write routines,
a guest may set 's->regs.mm_index' such that it leads to infinite
recursion. Check mm_index value to avoid it.

Reported-by: Ren Ding <rding@gatech.edu>
Reported-by: Hanqing Zhao <hanqing@gatech.edu>
Reported-by: Yi Ren <c4tren@gmail.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 hw/display/ati.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Update v2: add check before recursive call
  -> https://lists.gnu.org/archive/html/qemu-devel/2020-06/msg00781.html

diff --git a/hw/display/ati.c b/hw/display/ati.c
index 065f197678..bda4a2d816 100644
--- a/hw/display/ati.c
+++ b/hw/display/ati.c
@@ -285,7 +285,7 @@ static uint64_t ati_mm_read(void *opaque, hwaddr addr, unsigned int size)
             if (idx <= s->vga.vram_size - size) {
                 val = ldn_le_p(s->vga.vram_ptr + idx, size);
             }
-        } else {
+        } else if (s->regs.mm_index > MM_DATA + 3) {
             val = ati_mm_read(s, s->regs.mm_index + addr - MM_DATA, size);
         }
         break;
@@ -520,7 +520,7 @@ static void ati_mm_write(void *opaque, hwaddr addr,
             if (idx <= s->vga.vram_size - size) {
                 stn_le_p(s->vga.vram_ptr + idx, size, data);
             }
-        } else {
+        } else if (s->regs.mm_index > MM_DATA + 3) {
             ati_mm_write(s, s->regs.mm_index + addr - MM_DATA, data, size);
         }
         break;
-- 
2.26.2
Re: [PATCH v2] ati-vga: check mm_index before recursive call
Posted by Philippe Mathieu-Daudé 5 years, 8 months ago 
On 6/3/20 8:55 PM, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
> 
> While accessing VGA registers via ati_mm_read/write routines,
> a guest may set 's->regs.mm_index' such that it leads to infinite
> recursion. Check mm_index value to avoid it.
> 
> Reported-by: Ren Ding <rding@gatech.edu>
> Reported-by: Hanqing Zhao <hanqing@gatech.edu>
> Reported-by: Yi Ren <c4tren@gmail.com>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  hw/display/ati.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> Update v2: add check before recursive call
>   -> https://lists.gnu.org/archive/html/qemu-devel/2020-06/msg00781.html
> 
> diff --git a/hw/display/ati.c b/hw/display/ati.c
> index 065f197678..bda4a2d816 100644
> --- a/hw/display/ati.c
> +++ b/hw/display/ati.c
> @@ -285,7 +285,7 @@ static uint64_t ati_mm_read(void *opaque, hwaddr addr, unsigned int size)
>              if (idx <= s->vga.vram_size - size) {
>                  val = ldn_le_p(s->vga.vram_ptr + idx, size);
>              }
> -        } else {
> +        } else if (s->regs.mm_index > MM_DATA + 3) {
>              val = ati_mm_read(s, s->regs.mm_index + addr - MM_DATA, size);

We usually log unexpected guest accesses with:

           } else {
               qemu_log_mask(LOG_GUEST_ERROR, ...

>          }
>          break;
> @@ -520,7 +520,7 @@ static void ati_mm_write(void *opaque, hwaddr addr,
>              if (idx <= s->vga.vram_size - size) {
>                  stn_le_p(s->vga.vram_ptr + idx, size, data);
>              }
> -        } else {
> +        } else if (s->regs.mm_index > MM_DATA + 3) {
>              ati_mm_write(s, s->regs.mm_index + addr - MM_DATA, data, size);

Ditto:

           } else {
               qemu_log_mask(LOG_GUEST_ERROR, ...

>          }
>          break;
>
Re: [PATCH v2] ati-vga: check mm_index before recursive call
Posted by BALATON Zoltan 5 years, 8 months ago 
On Thu, 4 Jun 2020, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
>
> While accessing VGA registers via ati_mm_read/write routines,
> a guest may set 's->regs.mm_index' such that it leads to infinite
> recursion. Check mm_index value to avoid it.
>
> Reported-by: Ren Ding <rding@gatech.edu>
> Reported-by: Hanqing Zhao <hanqing@gatech.edu>
> Reported-by: Yi Ren <c4tren@gmail.com>

Suggested-by: BALATON Zoltan <balaton@eik.bme.hu>

therefore I think this should work but someone else should give 
Reviewed-by to cross check this.

Regards,
BALATON Zoltan

> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
> hw/display/ati.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> Update v2: add check before recursive call
>  -> https://lists.gnu.org/archive/html/qemu-devel/2020-06/msg00781.html
>
> diff --git a/hw/display/ati.c b/hw/display/ati.c
> index 065f197678..bda4a2d816 100644
> --- a/hw/display/ati.c
> +++ b/hw/display/ati.c
> @@ -285,7 +285,7 @@ static uint64_t ati_mm_read(void *opaque, hwaddr addr, unsigned int size)
>             if (idx <= s->vga.vram_size - size) {
>                 val = ldn_le_p(s->vga.vram_ptr + idx, size);
>             }
> -        } else {
> +        } else if (s->regs.mm_index > MM_DATA + 3) {
>             val = ati_mm_read(s, s->regs.mm_index + addr - MM_DATA, size);
>         }
>         break;
> @@ -520,7 +520,7 @@ static void ati_mm_write(void *opaque, hwaddr addr,
>             if (idx <= s->vga.vram_size - size) {
>                 stn_le_p(s->vga.vram_ptr + idx, size, data);
>             }
> -        } else {
> +        } else if (s->regs.mm_index > MM_DATA + 3) {
>             ati_mm_write(s, s->regs.mm_index + addr - MM_DATA, data, size);
>         }
>         break;
>
Re: [PATCH v2] ati-vga: check mm_index before recursive call
Posted by Daniel P. Berrangé 5 years, 8 months ago 
On Thu, Jun 04, 2020 at 12:25:22AM +0530, P J P wrote:
> From: Prasad J Pandit <pjp@fedoraproject.org>
> 
> While accessing VGA registers via ati_mm_read/write routines,
> a guest may set 's->regs.mm_index' such that it leads to infinite
> recursion. Check mm_index value to avoid it.

So this is a denial of service security issue. Is there any CVE
assigned for this ?

> Reported-by: Ren Ding <rding@gatech.edu>
> Reported-by: Hanqing Zhao <hanqing@gatech.edu>
> Reported-by: Yi Ren <c4tren@gmail.com>
> Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
> ---
>  hw/display/ati.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> Update v2: add check before recursive call
>   -> https://lists.gnu.org/archive/html/qemu-devel/2020-06/msg00781.html
> 
> diff --git a/hw/display/ati.c b/hw/display/ati.c
> index 065f197678..bda4a2d816 100644
> --- a/hw/display/ati.c
> +++ b/hw/display/ati.c
> @@ -285,7 +285,7 @@ static uint64_t ati_mm_read(void *opaque, hwaddr addr, unsigned int size)
>              if (idx <= s->vga.vram_size - size) {
>                  val = ldn_le_p(s->vga.vram_ptr + idx, size);
>              }
> -        } else {
> +        } else if (s->regs.mm_index > MM_DATA + 3) {
>              val = ati_mm_read(s, s->regs.mm_index + addr - MM_DATA, size);
>          }
>          break;
> @@ -520,7 +520,7 @@ static void ati_mm_write(void *opaque, hwaddr addr,
>              if (idx <= s->vga.vram_size - size) {
>                  stn_le_p(s->vga.vram_ptr + idx, size, data);
>              }
> -        } else {
> +        } else if (s->regs.mm_index > MM_DATA + 3) {
>              ati_mm_write(s, s->regs.mm_index + addr - MM_DATA, data, size);
>          }
>          break;
> -- 
> 2.26.2
> 
> 

Regards,
Daniel
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Re: [PATCH v2] ati-vga: check mm_index before recursive call
Posted by P J P 5 years, 8 months ago 
+-- On Wed, 3 Jun 2020, Philippe Mathieu-Daudé wrote --+
| > -        } else {
| > +        } else if (s->regs.mm_index > MM_DATA + 3) {
| >              val = ati_mm_read(s, s->regs.mm_index + addr - MM_DATA, size);
| 
| We usually log unexpected guest accesses with:
| 
|            } else {
|                qemu_log_mask(LOG_GUEST_ERROR, ...
| 
| > -        } else {
| > +        } else if (s->regs.mm_index > MM_DATA + 3) {
| >              ati_mm_write(s, s->regs.mm_index + addr - MM_DATA, data, size);
| 
| Ditto:
| 
|            } else {
|                qemu_log_mask(LOG_GUEST_ERROR, ...

+-- On Thu, 4 Jun 2020, Daniel P. Berrangé wrote --+
| On Thu, Jun 04, 2020 at 12:25:22AM +0530, P J P wrote:
| > While accessing VGA registers via ati_mm_read/write routines,
| > a guest may set 's->regs.mm_index' such that it leads to infinite
| > recursion. Check mm_index value to avoid it.
| 
| So this is a denial of service security issue. Is there any CVE
| assigned for this ?

Yes, just sent a revised patch v3 with above changes and CVE-ID.

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
8685 545E B54C 486B C6EB 271E E285 8B5A F050 DE8D

Patchew 2.1-devel-b67e4c2

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