drm/radeon: r6xx/r7xx possible security issue, system ram access

This patch workaround a possible security issue which can allow
user to abuse drm on r6xx/r7xx hw to access any system ram memory.
This patch doesn't break userspace, it detect "valid" old use of
CB_COLOR[0-7]_FRAG & CB_COLOR[0-7]_TILE registers and overwritte
the address these registers are pointing to with the one of the
last color buffer. This workaround will work for old mesa &
xf86-video-ati and any old user which did use similar register
programming pattern as those (we expect that there is no others
user of those ioctl except possibly a malicious one). This patch
add a warning if it detects such usage, warning encourage people
to update their mesa & xf86-video-ati. New userspace will submit
proper relocation.

Fix for xf86-video-ati / mesa (this kernel patch is enough to
prevent abuse, fix for userspace are to set proper cs stream and
avoid kernel warning) :
http://cgit.freedesktop.org/xorg/driver/xf86-video-ati/commit/?id=95d63e408cc88b6934bec84a0b1ef94dfe8bee7b
http://cgit.freedesktop.org/mesa/mesa/commit/?id=46dc6fd3ed5ef96cda53641a97bc68c3bc104a9f

Abusing this register to perform system ram memory is not easy,
here is outline on how it could be achieve. First attacker must
have access to the drm device and be able to submit command stream
throught cs ioctl. Then attacker must build a proper command stream
for r6xx/r7xx hw which will abuse the FRAG or TILE buffer to
overwrite the GPU GART which is in VRAM. To achieve so attacker
as to setup CB_COLOR[0-7]_FRAG or CB_COLOR[0-7]_TILE to point
to the GPU GART, then it has to find a way to write predictable
value into those buffer (with little cleverness i believe this
can be done but this is an hard task). Once attacker have such
program it can overwritte GPU GART to program GPU gart to point
anywhere in system memory. It then can reusse same method as he
used to reprogram GART to overwritte the system ram through the
GART mapping. In the process the attacker has to be carefull to
not overwritte any sensitive area of the GART table, like ring
or IB gart entry as it will more then likely lead to GPU lockup.
Bottom line is that i think it's very hard to use this flaw
to get system ram access but in theory one can achieve so.

Side note: I am not aware of anyone ever using the GPU as an
attack vector, nevertheless we take great care in the opensource
driver to try to detect and forbid malicious use of GPU. I don't
think the closed source driver are as cautious as we are.

Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@linux.ie>

1 files changed, 25 insertions, 0 deletions

diff --git a/drivers/gpu/drm/radeon/r600d.h b/drivers/gpu/drm/radeon/r600d.h
index 05894ed..3048088 100644
--- a/drivers/gpu/drm/radeon/r600d.h
+++ b/drivers/gpu/drm/radeon/r600d.h
@@ -882,4 +882,29 @@
 #define		S_000E60_SOFT_RESET_VMC(x)		(((x) & 1) << 17)
 
 #define R_005480_HDP_MEM_COHERENCY_FLUSH_CNTL		0x5480
+
+#define R_0280E0_CB_COLOR0_FRAG                      0x0280E0
+#define   S_0280E0_BASE_256B(x)                        (((x) & 0xFFFFFFFF) << 0)
+#define   G_0280E0_BASE_256B(x)                        (((x) >> 0) & 0xFFFFFFFF)
+#define   C_0280E0_BASE_256B                           0x00000000
+#define R_0280E4_CB_COLOR1_FRAG                      0x0280E4
+#define R_0280E8_CB_COLOR2_FRAG                      0x0280E8
+#define R_0280EC_CB_COLOR3_FRAG                      0x0280EC
+#define R_0280F0_CB_COLOR4_FRAG                      0x0280F0
+#define R_0280F4_CB_COLOR5_FRAG                      0x0280F4
+#define R_0280F8_CB_COLOR6_FRAG                      0x0280F8
+#define R_0280FC_CB_COLOR7_FRAG                      0x0280FC
+#define R_0280C0_CB_COLOR0_TILE                      0x0280C0
+#define   S_0280C0_BASE_256B(x)                        (((x) & 0xFFFFFFFF) << 0)
+#define   G_0280C0_BASE_256B(x)                        (((x) >> 0) & 0xFFFFFFFF)
+#define   C_0280C0_BASE_256B                           0x00000000
+#define R_0280C4_CB_COLOR1_TILE                      0x0280C4
+#define R_0280C8_CB_COLOR2_TILE                      0x0280C8
+#define R_0280CC_CB_COLOR3_TILE                      0x0280CC
+#define R_0280D0_CB_COLOR4_TILE                      0x0280D0
+#define R_0280D4_CB_COLOR5_TILE                      0x0280D4
+#define R_0280D8_CB_COLOR6_TILE                      0x0280D8
+#define R_0280DC_CB_COLOR7_TILE                      0x0280DC
+
+
 #endif