[PATCH v3 8/8] hw/display/artist: Prevent out of VRAM buffer accesses

[Helge Deller]

Simplify bounds checks by changing some parameters like row or column
numbers to become unsigned instead of signed.
With that we can check if the calculated offset is bigger than the size
of the VRAM region and bail out if not.

Reported-by: LLVM libFuzzer
Buglink: https://bugs.launchpad.net/qemu/+bug/1880326
Signed-off-by: Helge Deller <deller@gmx.de>
---
 hw/display/artist.c | 59 +++++++++++++++++++++++++++------------------
 1 file changed, 36 insertions(+), 23 deletions(-)

diff --git a/hw/display/artist.c b/hw/display/artist.c
index 47de17b9e9..c2fa097020 100644
--- a/hw/display/artist.c
+++ b/hw/display/artist.c
@@ -203,12 +203,12 @@ static int16_t artist_get_y(uint32_t reg)
 }

 static void artist_invalidate_lines(struct vram_buffer *buf,
-                                    int starty, int height)
+                                    unsigned int starty, unsigned int height)
 {
-    int start = starty * buf->width;
-    int size = height * buf->width;
+    unsigned int start = starty * buf->width;
+    unsigned int size = height * buf->width;

-    if (start + size <= buf->size) {
+    if (start + size < buf->size) {
         memory_region_set_dirty(&buf->mr, start, size);
     }
 }
@@ -274,15 +274,15 @@ static artist_rop_t artist_get_op(ARTISTState *s)
 }

 static void artist_rop8(ARTISTState *s, struct vram_buffer *buf,
-                        int offset, uint8_t val)
+                        unsigned int offset, uint8_t val)
 {
     const artist_rop_t op = artist_get_op(s);
     uint8_t plane_mask;
     uint8_t *dst;

-    if (offset < 0 || offset >= buf->size) {
+    if (offset >= buf->size) {
         qemu_log_mask(LOG_GUEST_ERROR,
-                      "rop8 offset:%d bufsize:%u\n", offset, buf->size);
+                      "rop8 offset:%u bufsize:%u\n", offset, buf->size);
         return;
     }
     dst = buf->data + offset;
@@ -464,12 +464,14 @@ static void vram_bit_write(ARTISTState *s, int posx, int 
posy, bool incr_x,
     }
 }

-static void block_move(ARTISTState *s, int source_x, int source_y, int dest_x,
-                       int dest_y, int width, int height)
+static void block_move(ARTISTState *s,
+                       unsigned int source_x, unsigned int source_y,
+                       unsigned int dest_x,   unsigned int dest_y,
+                       unsigned int width,    unsigned int height)
 {
     struct vram_buffer *buf;
     int line, endline, lineincr, startcolumn, endcolumn, columnincr, column;
-    uint32_t dst, src;
+    unsigned int dst, src;

     trace_artist_block_move(source_x, source_y, dest_x, dest_y, width, height);

@@ -481,6 +483,12 @@ static void block_move(ARTISTState *s, int source_x, int 
source_y, int dest_x,
     }

     buf = &s->vram_buffer[ARTIST_BUFFER_AP];
+    if (height > buf->height) {
+        height = buf->height;
+    }
+    if (width > buf->width) {
+        width = buf->width;
+    }

     if (dest_y > source_y) {
         /* move down */
@@ -507,24 +515,27 @@ static void block_move(ARTISTState *s, int source_x, int 
source_y, int dest_x,
     }

     for ( ; line != endline; line += lineincr) {
-        src = source_x + ((line + source_y) * buf->width);
-        dst = dest_x + ((line + dest_y) * buf->width);
+        src = source_x + ((line + source_y) * buf->width) + startcolumn;
+        dst = dest_x + ((line + dest_y) * buf->width) + startcolumn;

         for (column = startcolumn; column != endcolumn; column += columnincr) {
-            if (dst + column > buf->size || src + column > buf->size) {
+            if (dst > buf->size || src > buf->size) {
                 continue;
             }
-            artist_rop8(s, buf, dst + column, buf->data[src + column]);
+            artist_rop8(s, buf, dst, buf->data[src]);
+            src += columnincr;
+            dst += columnincr;
         }
     }

     artist_invalidate_lines(buf, dest_y, height);
 }

-static void fill_window(ARTISTState *s, int startx, int starty,
-                        int width, int height)
+static void fill_window(ARTISTState *s,
+                        unsigned int startx, unsigned int starty,
+                        unsigned int width,  unsigned int height)
 {
-    uint32_t offset;
+    unsigned int offset;
     uint8_t color = artist_get_color(s);
     struct vram_buffer *buf;
     int x, y;
@@ -561,7 +572,9 @@ static void fill_window(ARTISTState *s, int startx, int 
starty,
     artist_invalidate_lines(buf, starty, height);
 }

-static void draw_line(ARTISTState *s, int x1, int y1, int x2, int y2,
+static void draw_line(ARTISTState *s,
+                      unsigned int x1, unsigned int y1,
+                      unsigned int x2, unsigned int y2,
                       bool update_start, int skip_pix, int max_pix)
 {
     struct vram_buffer *buf = &s->vram_buffer[ARTIST_BUFFER_AP];
@@ -636,7 +649,7 @@ static void draw_line(ARTISTState *s, int x1, int y1, int 
x2, int y2,
     color = artist_get_color(s);

     do {
-        int ofs;
+        unsigned int ofs;

         if (c1) {
             ofs = x * s->width + y;
@@ -768,9 +781,9 @@ static void font_write16(ARTISTState *s, uint16_t val)
     uint16_t mask;
     int i;

-    int startx = artist_get_x(s->vram_start);
-    int starty = artist_get_y(s->vram_start) + s->font_write_pos_y;
-    int offset = starty * s->width + startx;
+    unsigned int startx = artist_get_x(s->vram_start);
+    unsigned int starty = artist_get_y(s->vram_start) + s->font_write_pos_y;
+    unsigned int offset = starty * s->width + startx;

     buf = &s->vram_buffer[ARTIST_BUFFER_AP];

@@ -1138,7 +1151,7 @@ static void artist_vram_write(void *opaque, hwaddr addr, 
uint64_t val,
     struct vram_buffer *buf;
     int posy = (addr >> 11) & 0x3ff;
     int posx = addr & 0x7ff;
-    uint32_t offset;
+    unsigned int offset;
     trace_artist_vram_write(size, addr, val);

     if (s->cmap_bm_access) {
--
2.21.3