From: Vincent Fazio <vfazio@gmail.com>
Previously, if the build host's libc did not define MAP_FIXED_NOREPLACE
or if the running kernel didn't support that flag, it was possible for
pgd_find_hole_fallback to munmap an incorrect address which could lead to
SIGSEGV if the range happened to overlap with the mapped address of the
QEMU binary.
mmap(0x1000, 22261224, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE,
-1, 0) = 0x7f889d331000
munmap(0x1000, 22261224) = 0
--- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_MAPERR, si_addr=0x84b817} ---
++ killed by SIGSEGV +++
Now, always munmap the address returned by mmap.
Fixes: 2667e069e7b5 ("linux-user: don't use MAP_FIXED in
pgd_find_hole_fallback")
Signed-off-by: Vincent Fazio <vfazio@gmail.com>