blob: afaf9162372d1e11430c54253f58d5f49398383e (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
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
|
