hw/display/tcx: Fix out-of-bounds access in tcx_blit_writel

This patch addresses a potential out-of-bounds memory access issue in the
tcx_blit_writel function. It adds bounds checking to ensure that memory
accesses do not exceed the allocated VRAM size. If an out-of-bounds access
is detected, an error is logged using qemu_log_mask.

ASAN log:
==2960379==ERROR: AddressSanitizer: SEGV on unknown address 0x7f524752fd01 (pc 0x7f525c2c4881 bp 0x7ffdaf87bfd0 sp 0x7ffdaf87b788 T0)
==2960379==The signal is caused by a READ memory access.
    #0 0x7f525c2c4881 in memcpy string/../sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S:222
    #1 0x55aa782bd5b1 in __asan_memcpy llvm/compiler-rt/lib/asan/asan_interceptors_memintrinsics.cpp:22:3
    #2 0x55aa7854dedd in tcx_blit_writel hw/display/tcx.c:590:13

Reproducer:
cat << EOF | qemu-system-sparc -display none \
-machine accel=qtest, -m 512M -machine LX -m 256 -qtest stdio
writel 0x562e98c4 0x3d92fd01
EOF

Signed-off-by: Zheyu Ma <[email protected]>
Message-Id: <[email protected]>

hw/display/tcx.c

@@ -33,6 +33,7 @@
 #include "migration/vmstate.h"
 #include "qemu/error-report.h"
 #include "qemu/module.h"
+#include "qemu/log.h"
 #include "qom/object.h"
 
 #define TCX_ROM_FILE "QEMU,tcx.bin"
@@ -577,6 +578,14 @@ static void tcx_blit_writel(void *opaque, hwaddr addr,
         addr = (addr >> 3) & 0xfffff;
         adsr = val & 0xffffff;
         len = ((val >> 24) & 0x1f) + 1;
+
+        if (addr + len > s->vram_size || adsr + len > s->vram_size) {
+            qemu_log_mask(LOG_GUEST_ERROR,
+                          "%s: VRAM access out of bounds. addr: 0x%lx, adsr: 0x%x, len: %u\n",
+                          __func__, addr, adsr, len);
+            return;
+        }
+
         if (adsr == 0xffffff) {
             memset(&s->vram[addr], s->tmpblit, len);
             if (s->depth == 24) {