From: Li Qiang <liqiang6-s@360.cn>

When doing bitblt copy in backward mode, we should minus the
blt width first just like the adding in the forward mode. This
can avoid the oob access of the front of vga's vram.

Signed-off-by: Li Qiang <liqiang6-s@360.cn>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 1485938101-26602-1-git-send-email-kraxel@redhat.com
Message-id: 5887254f.863a240a.2c122.5500@mx.google.com

{ kraxel: with backward blits (negative pitch) addr is the topmost
          address, so check it as-is against vram size ]

Cc: qemu-stable@nongnu.org
Cc: P J P <ppandit@redhat.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Wolfgang Bumiller <w.bumiller@proxmox.com>
Fixes: d3532a0db02296e687711b8cdc7791924efccea0 (CVE-2014-8106)
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
---
 hw/display/cirrus_vga.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/hw/display/cirrus_vga.c b/hw/display/cirrus_vga.c
index 7db6409..16f27e8 100644
--- a/hw/display/cirrus_vga.c
+++ b/hw/display/cirrus_vga.c
@@ -274,10 +274,9 @@ static bool blit_region_is_unsafe(struct CirrusVGAState *s,
 {
     if (pitch < 0) {
         int64_t min = addr
-            + ((int64_t)s->cirrus_blt_height-1) * pitch;
-        int32_t max = addr
-            + s->cirrus_blt_width;
-        if (min < 0 || max > s->vga.vram_size) {
+            + ((int64_t)s->cirrus_blt_height - 1) * pitch
+            - s->cirrus_blt_width;
+        if (min < -1 || addr >= s->vga.vram_size) {
             return true;
         }
     } else {
-- 
1.8.3.1

On 02/02/17 09:23, Gerd Hoffmann wrote:
> From: Li Qiang <liqiang6-s@360.cn>
> 
> When doing bitblt copy in backward mode, we should minus the
> blt width first just like the adding in the forward mode. This
> can avoid the oob access of the front of vga's vram.
> 
> Signed-off-by: Li Qiang <liqiang6-s@360.cn>
> Reviewed-by: Laszlo Ersek <lersek@redhat.com>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> Message-id: 1485938101-26602-1-git-send-email-kraxel@redhat.com
> Message-id: 5887254f.863a240a.2c122.5500@mx.google.com
> 
> { kraxel: with backward blits (negative pitch) addr is the topmost
>           address, so check it as-is against vram size ]
> 
> Cc: qemu-stable@nongnu.org
> Cc: P J P <ppandit@redhat.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Wolfgang Bumiller <w.bumiller@proxmox.com>
> Fixes: d3532a0db02296e687711b8cdc7791924efccea0 (CVE-2014-8106)
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
>  hw/display/cirrus_vga.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/display/cirrus_vga.c b/hw/display/cirrus_vga.c
> index 7db6409..16f27e8 100644
> --- a/hw/display/cirrus_vga.c
> +++ b/hw/display/cirrus_vga.c
> @@ -274,10 +274,9 @@ static bool blit_region_is_unsafe(struct CirrusVGAState *s,
>  {
>      if (pitch < 0) {
>          int64_t min = addr
> -            + ((int64_t)s->cirrus_blt_height-1) * pitch;
> -        int32_t max = addr
> -            + s->cirrus_blt_width;
> -        if (min < 0 || max > s->vga.vram_size) {
> +            + ((int64_t)s->cirrus_blt_height - 1) * pitch
> +            - s->cirrus_blt_width;
> +        if (min < -1 || addr >= s->vga.vram_size) {
>              return true;
>          }
>      } else {
> 

My inner pedant wishes to observe that my review concerned the patch as
modified by you, so for complete accuracy, my R-b should be at the
bottom, under your S-o-b.

Not sure if this merits a PULLv2, I just needed to "silence to voices".

Thanks
Laszlo

> > Signed-off-by: Li Qiang <liqiang6-s@360.cn>
> > Reviewed-by: Laszlo Ersek <lersek@redhat.com>
> > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> > Message-id: 1485938101-26602-1-git-send-email-kraxel@redhat.com
> > Message-id: 5887254f.863a240a.2c122.5500@mx.google.com
> > 
> > { kraxel: with backward blits (negative pitch) addr is the topmost
> >           address, so check it as-is against vram size ]
> > 
> > Cc: qemu-stable@nongnu.org
> > Cc: P J P <ppandit@redhat.com>
> > Cc: Laszlo Ersek <lersek@redhat.com>
> > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > Cc: Wolfgang Bumiller <w.bumiller@proxmox.com>
> > Fixes: d3532a0db02296e687711b8cdc7791924efccea0 (CVE-2014-8106)
> > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

> My inner pedant wishes to observe that my review concerned the patch as
> modified by you, so for complete accuracy, my R-b should be at the
> bottom, under your S-o-b.
> 
> Not sure if this merits a PULLv2, I just needed to "silence to voices".

Oops.  The message ids are kinda f*cked up too.  Guess I shouldn't trust
the patches tool too much when it comes to non-trivial patch flows.

I'll respin the pull request.

cheers,
  Gerd