[PULL 3/5] linux-user/elfload: munmap proper address in pgd_find_hole_fallback

[Laurent Vivier <laurent@vivier.eu>]

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>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20210131061849.12615-1-vfazio@xes-inc.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
---
 linux-user/elfload.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 140a9716324d..174ee7bad677 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -2209,7 +2209,7 @@ static uintptr_t pgd_find_hole_fallback(uintptr_t guest_size, uintptr_t brk,
             void * mmap_start = mmap((void *) align_start, guest_size,
                                      PROT_NONE, flags, -1, 0);
             if (mmap_start != MAP_FAILED) {
-                munmap((void *) align_start, guest_size);
+                munmap(mmap_start, guest_size);
                 if (MAP_FIXED_NOREPLACE != 0 ||
                     mmap_start == (void *) align_start) {
                     return (uintptr_t) mmap_start + offset;
-- 
2.29.2