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* [PATCH 0/3] hw/display/artist: Fix out-of-buffer accesses found while fuzzing
@ 2020-05-23 19:15 Philippe Mathieu-Daudé
  2020-05-23 19:15 ` [PATCH 1/3] hw/display/artist: Check offset in draw_line to avoid buffer over-run Philippe Mathieu-Daudé
                   ` (2 more replies)
  0 siblings, 3 replies; 4+ messages in thread
From: Philippe Mathieu-Daudé @ 2020-05-23 19:15 UTC (permalink / raw)
  To: Helge Deller, qemu-devel, Richard Henderson, Sven Schnelle
  Cc: Alexander Bulekov, Philippe Mathieu-Daudé

Fix various out-of-range buffer access in the artist device
emulation. Bugs found using libFuzzer (docs/devel/fuzzing.txt).

Philippe Mathieu-Daudé (3):
  hw/display/artist: Check offset in draw_line to avoid buffer over-run
  hw/display/artist: Refactor artist_rop8() to avoid buffer over-run
  hw/display/artist: Check offset in block_move to avoid buffer
    over-read

 hw/display/artist.c | 54 +++++++++++++++++++++++++++++++--------------
 1 file changed, 37 insertions(+), 17 deletions(-)

-- 
2.21.3



^ permalink raw reply	[flat|nested] 4+ messages in thread

* [PATCH 1/3] hw/display/artist: Check offset in draw_line to avoid buffer over-run
  2020-05-23 19:15 [PATCH 0/3] hw/display/artist: Fix out-of-buffer accesses found while fuzzing Philippe Mathieu-Daudé
@ 2020-05-23 19:15 ` Philippe Mathieu-Daudé
  2020-05-23 19:15 ` [PATCH 2/3] hw/display/artist: Refactor artist_rop8() " Philippe Mathieu-Daudé
  2020-05-23 19:15 ` [PATCH 3/3] hw/display/artist: Check offset in block_move to avoid buffer over-read Philippe Mathieu-Daudé
  2 siblings, 0 replies; 4+ messages in thread
From: Philippe Mathieu-Daudé @ 2020-05-23 19:15 UTC (permalink / raw)
  To: Helge Deller, qemu-devel, Richard Henderson, Sven Schnelle
  Cc: Alexander Bulekov, Philippe Mathieu-Daudé

Invalid I/O writes can craft an offset out of the vram_buffer
range.

We avoid:

  Program terminated with signal SIGSEGV, Segmentation fault.
  284             *dst &= ~plane_mask;
  (gdb) bt
  #0  0x000055d5dccdc5c0 in artist_rop8 (s=0x55d5defee510, dst=0x7f8e84ed8216 <error: Cannot access memory at address 0x7f8e84ed8216>, val=0 '\000') at hw/display/artist.c:284
  #1  0x000055d5dccdcf83 in fill_window (s=0x55d5defee510, startx=22, starty=5674, width=65, height=5697) at hw/display/artist.c:551
  #2  0x000055d5dccddfb9 in artist_reg_write (opaque=0x55d5defee510, addr=1051140, val=4265537, size=4) at hw/display/artist.c:902
  #3  0x000055d5dcb42a7c in memory_region_write_accessor (mr=0x55d5defeea10, addr=1051140, value=0x7ffe57db08c8, size=4, shift=0, mask=4294967295, attrs=...) at memory.c:483

Reported-by: LLVM libFuzzer
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
 hw/display/artist.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/hw/display/artist.c b/hw/display/artist.c
index 6261bfe65b..3c2550f6db 100644
--- a/hw/display/artist.c
+++ b/hw/display/artist.c
@@ -557,7 +557,7 @@ static void fill_window(ARTISTState *s, int startx, int starty,
 static void draw_line(ARTISTState *s, int x1, int y1, int x2, int y2,
                       bool update_start, int skip_pix, int max_pix)
 {
-    struct vram_buffer *buf;
+    struct vram_buffer *buf = &s->vram_buffer[ARTIST_BUFFER_AP];
     uint8_t color;
     int dx, dy, t, e, x, y, incy, diago, horiz;
     bool c1;
@@ -565,6 +565,12 @@ static void draw_line(ARTISTState *s, int x1, int y1, int x2, int y2,
 
     trace_artist_draw_line(x1, y1, x2, y2);
 
+    if (x1 * y1 >= buf->size || x2 * y2 >= buf->size) {
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "draw_line (%d,%d) (%d,%d)\n", x1, y1, x2, y2);
+        return;
+    }
+
     if (update_start) {
         s->vram_start = (x2 << 16) | y2;
     }
@@ -622,7 +628,6 @@ static void draw_line(ARTISTState *s, int x1, int y1, int x2, int y2,
     x = x1;
     y = y1;
     color = artist_get_color(s);
-    buf = &s->vram_buffer[ARTIST_BUFFER_AP];
 
     do {
         if (c1) {
-- 
2.21.3



^ permalink raw reply	[flat|nested] 4+ messages in thread

* [PATCH 2/3] hw/display/artist: Refactor artist_rop8() to avoid buffer over-run
  2020-05-23 19:15 [PATCH 0/3] hw/display/artist: Fix out-of-buffer accesses found while fuzzing Philippe Mathieu-Daudé
  2020-05-23 19:15 ` [PATCH 1/3] hw/display/artist: Check offset in draw_line to avoid buffer over-run Philippe Mathieu-Daudé
@ 2020-05-23 19:15 ` Philippe Mathieu-Daudé
  2020-05-23 19:15 ` [PATCH 3/3] hw/display/artist: Check offset in block_move to avoid buffer over-read Philippe Mathieu-Daudé
  2 siblings, 0 replies; 4+ messages in thread
From: Philippe Mathieu-Daudé @ 2020-05-23 19:15 UTC (permalink / raw)
  To: Helge Deller, qemu-devel, Richard Henderson, Sven Schnelle
  Cc: Alexander Bulekov, Philippe Mathieu-Daudé

Invalid I/O writes can craft an offset out of the vram_buffer
range.
Instead of passing an unsafe pointer to artist_rop8(), pass the
vram_buffer and the offset. We can now check if the offset is
in range before accessing it.

We avoid:

  Program terminated with signal SIGSEGV, Segmentation fault.
  284             *dst &= ~plane_mask;
  (gdb) bt
  #0  0x000056367b2085c0 in artist_rop8 (s=0x56367d38b510, dst=0x7f9f972fffff <error: Cannot access memory at address 0x7f9f972fffff>, val=0 '\000') at hw/display/artist.c:284
  #1  0x000056367b209325 in draw_line (s=0x56367d38b510, x1=-20480, y1=-1, x2=0, y2=17920, update_start=true, skip_pix=-1, max_pix=-1) at hw/display/artist.c:646

Reported-by: LLVM libFuzzer
Buglink: https://bugs.launchpad.net/qemu/+bug/1880326
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
 hw/display/artist.c | 40 +++++++++++++++++++++++++---------------
 1 file changed, 25 insertions(+), 15 deletions(-)

diff --git a/hw/display/artist.c b/hw/display/artist.c
index 3c2550f6db..6f61b85a24 100644
--- a/hw/display/artist.c
+++ b/hw/display/artist.c
@@ -273,11 +273,20 @@ static artist_rop_t artist_get_op(ARTISTState *s)
     return (s->image_bitmap_op >> 8) & 0xf;
 }
 
-static void artist_rop8(ARTISTState *s, uint8_t *dst, uint8_t val)
+static void artist_rop8(ARTISTState *s, struct vram_buffer *buf,
+                        int offset, uint8_t val)
 {
-
     const artist_rop_t op = artist_get_op(s);
-    uint8_t plane_mask = s->plane_mask & 0xff;
+    uint8_t plane_mask;
+    uint8_t *dst;
+
+    if (offset < 0 || offset >= buf->size) {
+        qemu_log_mask(LOG_GUEST_ERROR,
+                      "rop8 offset:%d bufsize:%u\n", offset, buf->size);
+        return;
+    }
+    dst = buf->data + offset;
+    plane_mask = s->plane_mask & 0xff;
 
     switch (op) {
     case ARTIST_ROP_CLEAR:
@@ -381,7 +390,7 @@ static void vram_bit_write(ARTISTState *s, int posx, int posy, bool incr_x,
         }
 
         for (i = 0; i < pix_count; i++) {
-            artist_rop8(s, p + offset + pix_count - 1 - i,
+            artist_rop8(s, buf, offset + pix_count - 1 - i,
                         (data & 1) ? (s->plane_mask >> 24) : 0);
             data >>= 1;
         }
@@ -398,7 +407,7 @@ static void vram_bit_write(ARTISTState *s, int posx, int posy, bool incr_x,
         for (i = 3; i >= 0; i--) {
             if (!(s->image_bitmap_op & 0x20000000) ||
                 s->vram_bitmask & (1 << (28 + i))) {
-                artist_rop8(s, p + offset + 3 - i, data8[ROP8OFF(i)]);
+                artist_rop8(s, buf, offset + 3 - i, data8[ROP8OFF(i)]);
             }
         }
         memory_region_set_dirty(&buf->mr, offset, 3);
@@ -426,10 +435,10 @@ static void vram_bit_write(ARTISTState *s, int posx, int posy, bool incr_x,
             if (!(s->image_bitmap_op & 0x20000000) ||
                 (vram_bitmask & mask)) {
                 if (data & mask) {
-                    artist_rop8(s, p + offset + i, s->fg_color);
+                    artist_rop8(s, buf, offset + i, s->fg_color);
                 } else {
                     if (!(s->image_bitmap_op & 0x10000002)) {
-                        artist_rop8(s, p + offset + i, s->bg_color);
+                        artist_rop8(s, buf, offset + i, s->bg_color);
                     }
                 }
             }
@@ -507,7 +516,7 @@ static void block_move(ARTISTState *s, int source_x, int source_y, int dest_x,
             if (dst + column > buf->size || src + column > buf->size) {
                 continue;
             }
-            artist_rop8(s, buf->data + dst + column, buf->data[src + column]);
+            artist_rop8(s, buf, dst + column, buf->data[src + column]);
         }
     }
 
@@ -548,7 +557,7 @@ static void fill_window(ARTISTState *s, int startx, int starty,
         offset = y * s->width;
 
         for (x = startx; x < startx + width; x++) {
-            artist_rop8(s, buf->data + offset + x, color);
+            artist_rop8(s, buf, offset + x, color);
         }
     }
     artist_invalidate_lines(buf, starty, height);
@@ -561,7 +570,6 @@ static void draw_line(ARTISTState *s, int x1, int y1, int x2, int y2,
     uint8_t color;
     int dx, dy, t, e, x, y, incy, diago, horiz;
     bool c1;
-    uint8_t *p;
 
     trace_artist_draw_line(x1, y1, x2, y2);
 
@@ -630,16 +638,18 @@ static void draw_line(ARTISTState *s, int x1, int y1, int x2, int y2,
     color = artist_get_color(s);
 
     do {
+        int ofs;
+
         if (c1) {
-            p = buf->data + x * s->width + y;
+            ofs = x * s->width + y;
         } else {
-            p = buf->data + y * s->width + x;
+            ofs = y * s->width + x;
         }
 
         if (skip_pix > 0) {
             skip_pix--;
         } else {
-            artist_rop8(s, p, color);
+            artist_rop8(s, buf, ofs, color);
         }
 
         if (e > 0) {
@@ -773,10 +783,10 @@ static void font_write16(ARTISTState *s, uint16_t val)
     for (i = 0; i < 16; i++) {
         mask = 1 << (15 - i);
         if (val & mask) {
-            artist_rop8(s, buf->data + offset + i, color);
+            artist_rop8(s, buf, offset + i, color);
         } else {
             if (!(s->image_bitmap_op & 0x20000000)) {
-                artist_rop8(s, buf->data + offset + i, s->bg_color);
+                artist_rop8(s, buf, offset + i, s->bg_color);
             }
         }
     }
-- 
2.21.3



^ permalink raw reply	[flat|nested] 4+ messages in thread

* [PATCH 3/3] hw/display/artist: Check offset in block_move to avoid buffer over-read
  2020-05-23 19:15 [PATCH 0/3] hw/display/artist: Fix out-of-buffer accesses found while fuzzing Philippe Mathieu-Daudé
  2020-05-23 19:15 ` [PATCH 1/3] hw/display/artist: Check offset in draw_line to avoid buffer over-run Philippe Mathieu-Daudé
  2020-05-23 19:15 ` [PATCH 2/3] hw/display/artist: Refactor artist_rop8() " Philippe Mathieu-Daudé
@ 2020-05-23 19:15 ` Philippe Mathieu-Daudé
  2 siblings, 0 replies; 4+ messages in thread
From: Philippe Mathieu-Daudé @ 2020-05-23 19:15 UTC (permalink / raw)
  To: Helge Deller, qemu-devel, Richard Henderson, Sven Schnelle
  Cc: Alexander Bulekov, Philippe Mathieu-Daudé

Invalid I/O writes can craft an offset out of the vram_buffer
range.

We avoid:

  Program terminated with signal SIGSEGV, Segmentation fault.
  519                 artist_rop8(s, buf, dst + column, buf->data[src + column]);
  (gdb) bt
  #0  0x000055fa83b05e0a in block_move (s=0x55fa8647e510, source_x=0, source_y=0, dest_x=255, dest_y=-5, width=22, height=16705) at hw/display/artist.c:519
  #1  0x000055fa83b071da in artist_reg_write (opaque=0x55fa8647e510, addr=1051392, val=16777211, size=4) at hw/display/artist.c:954

Reported-by: LLVM libFuzzer
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
 hw/display/artist.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/hw/display/artist.c b/hw/display/artist.c
index 6f61b85a24..320e3c5050 100644
--- a/hw/display/artist.c
+++ b/hw/display/artist.c
@@ -513,6 +513,11 @@ static void block_move(ARTISTState *s, int source_x, int source_y, int dest_x,
         dst = dest_x + ((line + dest_y) * buf->width);
 
         for (column = startcolumn; column != endcolumn; column += columnincr) {
+            if ((int)src + column < 0 || src + column >= buf->size) {
+                qemu_log_mask(LOG_GUEST_ERROR,
+                              "block_move src:%d column:%d\n", src, column);
+                continue; /* FIXME */
+            }
             if (dst + column > buf->size || src + column > buf->size) {
                 continue;
             }
-- 
2.21.3



^ permalink raw reply	[flat|nested] 4+ messages in thread

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2020-05-23 19:15 [PATCH 0/3] hw/display/artist: Fix out-of-buffer accesses found while fuzzing Philippe Mathieu-Daudé
2020-05-23 19:15 ` [PATCH 1/3] hw/display/artist: Check offset in draw_line to avoid buffer over-run Philippe Mathieu-Daudé
2020-05-23 19:15 ` [PATCH 2/3] hw/display/artist: Refactor artist_rop8() " Philippe Mathieu-Daudé
2020-05-23 19:15 ` [PATCH 3/3] hw/display/artist: Check offset in block_move to avoid buffer over-read Philippe Mathieu-Daudé

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