linux-user/elfload: do not assume MAP_FIXED_NOREPLACE kernel support

Previously, pgd_find_hole_fallback assumed that if the build host's libc
had MAP_FIXED_NOREPLACE defined that the address returned by mmap would
match the requested address. This is not a safe assumption for Linux
kernels prior to 4.17

Now, we always compare mmap's resultant address with the requested
address and no longer short-circuit based on MAP_FIXED_NOREPLACE.

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: <20210131061930.14554-1-vfazio@xes-inc.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 174ee7bad677ea7d997a72be7590ab6281df48e8..e525901659d4944558506be4fbf9360ca9bf5a62 100644 (file)
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -2210,8 +2210,7 @@ static uintptr_t pgd_find_hole_fallback(uintptr_t guest_size, uintptr_t brk,
                                      PROT_NONE, flags, -1, 0);
             if (mmap_start != MAP_FAILED) {
                 munmap(mmap_start, guest_size);
-                if (MAP_FIXED_NOREPLACE != 0 ||
-                    mmap_start == (void *) align_start) {
+                if (mmap_start == (void *) align_start) {
                     return (uintptr_t) mmap_start + offset;
                 }
             }