Assertion failures in ati_reg_read_offs/ati_reg_write_offs

[Alexander Bulekov]

Hello,
While fuzzing, I found inputs that trigger assertion failures in
ati_reg_read_offs/ati_reg_write_offs

uint32_t extract32(uint32_t, int, int): Assertion `start >= 0 && length > 0 && length <= 32 - start' failed

#3 0x00007ffff6866092 in __GI___assert_fail (assertion=0x555556e760c0 <str> "start >= 0 && length > 0 && length <= 32 - start", file=0x555556e76120 <str> "/home/alxndr/Development/qemu/include/qemu/bitops.h", line=0x12c, function=0x555556e76180 <__PRETTY_FUNCTION__.extract32> "uint32_t extract32(uint32_t, int, int)") at assert.c:101
#4 0x000055555653d8a7 in ati_mm_read (opaque=<optimized out>, addr=0x1a, size=<optimized out>) at /home/alxndr/Development/qemu/include/qemu/log-for-trace.h:29
#5 0x000055555653c825 in ati_mm_read (opaque=<optimized out>, addr=0x4, size=<optimized out>) at /home/alxndr/Development/qemu/hw/display/ati.c:289
#6 0x000055555601446e in memory_region_read_accessor (mr=0x63100004dc20, addr=<optimized out>, value=<optimized out>, size=<optimized out>, shift=<optimized out>, mask=<optimized out>, attrs=...) at /home/alxndr/Development/qemu/memory.c:434
#7 0x0000555556001a70 in access_with_adjusted_size (addr=<optimized out>, value=<optimized out>, size=<optimized out>, access_size_min=<optimized out>, access_size_max=<optimized out>, access_fn=<optimized out>, mr=0x63100004dc20, attrs=...) at /home/alxndr/Development/qemu/memory.c:544
#8 0x0000555556001a70 in memory_region_dispatch_read1 (mr=0x63100004dc20, addr=0x4, pval=<optimized out>, size=0x4, attrs=...) at /home/alxndr/Development/qemu/memory.c:1396

I can reproduce it in qemu 5.0 built with using:
cat << EOF | ~/Development/qemu/build/i386-softmmu/qemu-system-i386 -M pc-q35-5.0 -device ati-vga -nographic -qtest stdio -monitor none -serial none
outl 0xcf8 0x80001018
outl 0xcfc 0xe2000000
outl 0xcf8 0x8000101c
outl 0xcf8 0x80001004
outw 0xcfc 0x7
outl 0xcf8 0x8000fa20
write 0xe2000004 0x1 0x1a
readq 0xe2000000
EOF

Similarly for ati_reg_write_offs:
cat << EOF | ~/Development/qemu/build/i386-softmmu/qemu-system-i386 -M pc-q35-5.0 -device ati-vga -nographic -qtest stdio -monitor none -serial none
outl 0xcf8 0x80001018
outl 0xcfc 0xe2000000
outl 0xcf8 0x8000101c
outl 0xcf8 0x80001004
outw 0xcfc 0x7
outl 0xcf8 0x8000fa20
write 0xe2000000 0x8 0x6a00000000006a00
EOF

I also attached the traces to this launchpad report, in case the formatting is broken:

qemu-system-i386 -M pc-q35-5.0 -device ati-vga -nographic -qtest stdio -monitor none -serial none < attachment

Please let me know if I can provide any further info.
-Alex