| From 74db251c34369bd32148864b3abea6d6586270dc Mon Sep 17 00:00:00 2001 |
| From: Gerd Hoffmann <kraxel@redhat.com> |
| Date: Fri, 10 Feb 2017 08:30:15 +0100 |
| Subject: [PATCH 3/3] cirrus: add blit_is_unsafe call to |
| cirrus_bitblt_cputovideo |
| |
| RH-Author: Gerd Hoffmann <kraxel@redhat.com> |
| Message-id: <1486715415-3462-4-git-send-email-kraxel@redhat.com> |
| Patchwork-id: 73773 |
| O-Subject: [virt-devel] [EMBARGOED RHEL-7.4 qemu-kvm PATCH 3/3] cirrus: add blit_is_unsafe call to cirrus_bitblt_cputovideo |
| Bugzilla: 1420492 |
| CVE: CVE-2017-2620/20170221 |
| RH-Acked-by: Paolo Bonzini <pbonzini@redhat.com> |
| RH-Acked-by: Laurent Vivier <lvivier@redhat.com> |
| RH-Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com> |
| |
| 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. |
| |
| Signed-off-by: Gerd Hoffmann <kraxel@redhat.com> |
| |
| Upstream: TBD (embargoed until Feb 21st) |
| Signed-off-by: Miroslav Rezanina <mrezanin@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 9a9501f..1b972db 100644 |
| |
| |
| @@ -894,6 +894,10 @@ 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]; |
| @@ -919,6 +923,10 @@ 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); |
| -- |
| 1.8.3.1 |
| |