[RESEND,v2,0/2] migration/xbzrle: fix two avx512 runtime issues

Message

Matheus Tavares Bernardino March 13, 2023, 6:58 p.m. UTC

This patchset strives to fix two bugs at xvzrle when --enable-avx512 is
used: an out-of-bounds write and an invalid argument to __builtin_ctz().

Those two errors can be seen in the test suite running:

$ ../configure --target-list=aarch64-softmmu --enable-sanitizers --enable-avx512bw
$ make tests/unit/test-xbzrle && ./tests/unit/test-xbzrle

  ==5518==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x62100000b100 at pc 0x561109a7714d bp 0x7ffed712a440 sp 0x7ffed712a430
  WRITE of size 1 at 0x62100000b100 thread T0
      #0 0x561109a7714c in uleb128_encode_small ../util/cutils.c:831
      #1 0x561109b67f6a in xbzrle_encode_buffer_avx512 ../migration/xbzrle.c:275
      #2 0x5611099a7428 in test_encode_decode_overflow ../tests/unit/test-xbzrle.c:153
      #3 0x7fb2fb65a58d  (/lib/x86_64-linux-gnu/libglib-2.0.so.0+0x7a58d)
      #4 0x7fb2fb65a333  (/lib/x86_64-linux-gnu/libglib-2.0.so.0+0x7a333)
      #5 0x7fb2fb65aa79 in g_test_run_suite (/lib/x86_64-linux-gnu/libglib-2.0.so.0+0x7aa79)
      #6 0x7fb2fb65aa94 in g_test_run (/lib/x86_64-linux-gnu/libglib-2.0.so.0+0x7aa94)
      #7 0x5611099a3a23 in main ../tests/unit/test-xbzrle.c:218
      #8 0x7fb2fa78c082 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x24082)
      #9 0x5611099a608d in _start (/qemu/build/tests/unit/test-xbzrle+0x28408d)
  
  0x62100000b100 is located 0 bytes to the right of 4096-byte region [0x62100000a100,0x62100000b100)
  allocated by thread T0 here:
      #0 0x7fb2fb823a06 in __interceptor_calloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cc:153
      #1 0x7fb2fb637ef0 in g_malloc0 (/lib/x86_64-linux-gnu/libglib-2.0.so.0+0x57ef0)
  
  ../migration/xbzrle.c:265: runtime error: passing zero to ctz(), which is not a valid argument

v1: https://lore.kernel.org/qemu-devel/[e-mail]/
(No changes since v1, only rebased on current master)

Matheus Tavares Bernardino (2):
  migration/xbzrle: use ctz64 to avoid undefined result
  migration/xbzrle: fix out-of-bounds write with axv512

 migration/xbzrle.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)