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From 74db251c34369bd32148864b3abea6d6586270dc Mon Sep 17 00:00:00 2001
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From: Gerd Hoffmann <kraxel@redhat.com>
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Date: Fri, 10 Feb 2017 08:30:15 +0100
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Subject: [PATCH 3/3] cirrus: add blit_is_unsafe call to
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cirrus_bitblt_cputovideo
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RH-Author: Gerd Hoffmann <kraxel@redhat.com>
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Message-id: <1486715415-3462-4-git-send-email-kraxel@redhat.com>
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Patchwork-id: 73773
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O-Subject: [virt-devel] [EMBARGOED RHEL-7.4 qemu-kvm PATCH 3/3] cirrus: add blit_is_unsafe call to cirrus_bitblt_cputovideo
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Bugzilla: 1420492
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CVE: CVE-2017-2620/20170221
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RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com>
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RH-Acked-by: Laurent Vivier <lvivier@redhat.com>
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RH-Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
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CIRRUS_BLTMODE_MEMSYSSRC blits do NOT check blit destination
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and blit width, at all. Oops. Fix it.
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Security impact: high.
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The missing blit destination check allows to write to host memory.
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Basically same as CVE-2014-8106 for the other blit variants.
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The missing blit width check allows to overflow cirrus_bltbuf,
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with the attractive target cirrus_srcptr (current cirrus_bltbuf write
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position) being located right after cirrus_bltbuf in CirrusVGAState.
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Due to cirrus emulation writing cirrus_bltbuf bytewise the attacker
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hasn't full control over cirrus_srcptr though, only one byte can be
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changed. Once the first byte has been modified further writes land
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elsewhere.
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Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
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Upstream: TBD (embargoed until Feb 21st)
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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hw/display/cirrus_vga.c | 8 ++++++++
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1 file changed, 8 insertions(+)
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diff --git a/hw/display/cirrus_vga.c b/hw/display/cirrus_vga.c
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index 9a9501f..1b972db 100644
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--- a/hw/display/cirrus_vga.c
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+++ b/hw/display/cirrus_vga.c
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@@ -894,6 +894,10 @@ static int cirrus_bitblt_cputovideo(CirrusVGAState * s)
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{
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int w;
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+ if (blit_is_unsafe(s, true)) {
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+ return 0;
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+ }
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+
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s->cirrus_blt_mode &= ~CIRRUS_BLTMODE_MEMSYSSRC;
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s->cirrus_srcptr = &s->cirrus_bltbuf[0];
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s->cirrus_srcptr_end = &s->cirrus_bltbuf[0];
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@@ -919,6 +923,10 @@ static int cirrus_bitblt_cputovideo(CirrusVGAState * s)
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}
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s->cirrus_srccounter = s->cirrus_blt_srcpitch * s->cirrus_blt_height;
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}
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+
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+ /* the blit_is_unsafe call above should catch this */
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+ assert(s->cirrus_blt_srcpitch <= CIRRUS_BLTBUFSIZE);
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+
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s->cirrus_srcptr = s->cirrus_bltbuf;
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s->cirrus_srcptr_end = s->cirrus_bltbuf + s->cirrus_blt_srcpitch;
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cirrus_update_memory_access(s);
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--
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1.8.3.1
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