1 files changed, 60 insertions, 0 deletions
diff --git a/main/xen/xsa209-0002-cirrus-add-blit_is_unsafe-call-to-cirrus_bitblt_cput.patch b/main/xen/xsa209-0002-cirrus-add-blit_is_unsafe-call-to-cirrus_bitblt_cput.patch
new file mode 100644
index 0000000000..afaf916237
--- /dev/null
+++ b/main/xen/xsa209-0002-cirrus-add-blit_is_unsafe-call-to-cirrus_bitblt_cput.patch
@@ -0,0 +1,60 @@
+From 15268f91fbe75b38a851c458aef74e693d646ea5 Mon Sep 17 00:00:00 2001
+From: Gerd Hoffmann <kraxel@redhat.com>
+Date: Tue, 21 Feb 2017 10:54:59 -0800
+Subject: [PATCH 2/2] cirrus: add blit_is_unsafe call to
+ cirrus_bitblt_cputovideo
+
+CIRRUS_BLTMODE_MEMSYSSRC blits do NOT check blit destination
+and blit width, at all.  Oops.  Fix it.
+
+Security impact: high.
+
+The missing blit destination check allows to write to host memory.
+Basically same as CVE-2014-8106 for the other blit variants.
+
+The missing blit width check allows to overflow cirrus_bltbuf,
+with the attractive target cirrus_srcptr (current cirrus_bltbuf write
+position) being located right after cirrus_bltbuf in CirrusVGAState.
+
+Due to cirrus emulation writing cirrus_bltbuf bytewise the attacker
+hasn't full control over cirrus_srcptr though, only one byte can be
+changed.  Once the first byte has been modified further writes land
+elsewhere.
+
+[ This is CVE-2017-2620 / XSA-209  - Ian Jackson ]
+
+Reported-by: Gerd Hoffmann <ghoffman@redhat.com>
+Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
+---
+ hw/display/cirrus_vga.c | 8 ++++++++
+ 1 file changed, 8 insertions(+)
+
+diff --git a/hw/display/cirrus_vga.c b/hw/display/cirrus_vga.c
+index 34a6900..5901250 100644
+--- a/hw/display/cirrus_vga.c
++++ b/tools/qemu-xen/hw/display/cirrus_vga.c
+@@ -865,6 +865,10 @@ static int cirrus_bitblt_cputovideo(CirrusVGAState * s)
+ {
+     int w;
+ 
++    if (blit_is_unsafe(s, true)) {
++        return 0;
++    }
++
+     s->cirrus_blt_mode &= ~CIRRUS_BLTMODE_MEMSYSSRC;
+     s->cirrus_srcptr = &s->cirrus_bltbuf[0];
+     s->cirrus_srcptr_end = &s->cirrus_bltbuf[0];
+@@ -890,6 +894,10 @@ static int cirrus_bitblt_cputovideo(CirrusVGAState * s)
+ 	}
+         s->cirrus_srccounter = s->cirrus_blt_srcpitch * s->cirrus_blt_height;
+     }
++
++    /* the blit_is_unsafe call above should catch this */
++    assert(s->cirrus_blt_srcpitch <= CIRRUS_BLTBUFSIZE);
++
+     s->cirrus_srcptr = s->cirrus_bltbuf;
+     s->cirrus_srcptr_end = s->cirrus_bltbuf + s->cirrus_blt_srcpitch;
+     cirrus_update_memory_access(s);
+-- 
+2.1.4
+