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linux-user: Fix MAP_FIXED_NOREPLACE on old kernels

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The man page states:
> Note that older kernels which do not recognize the MAP_FIXED_NOREPLACE
> flag will typically (upon detecting a collision with a preexisting
> mapping) fall back to a “non-MAP_FIXED” type of behavior: they will
> return an address that is different from the requested address.
> Therefore, backward-compatible software should check the returned
> address against the requested address.
https://man7.org/linux/man-pages/man2/mmap.2.html

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Message-Id: <20230802071754.14876-3-akihiko.odaki@daynix.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Akihiko Odaki 2023-08-02 16:17:48 +09:00 committed by Richard Henderson
parent c3dd50da0f
commit ddcdd8c48f
1 changed files with 17 additions and 5 deletions
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22
linux-user/mmap.c
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@ -263,7 +263,11 @@ static bool mmap_frag(abi_ulong real_start, abi_ulong start, abi_ulong last,
void *p = mmap(host_start, qemu_host_page_size,
target_to_host_prot(prot),
flags | MAP_ANONYMOUS, -1, 0);
if (p == MAP_FAILED) {
if (p != host_start) {
if (p != MAP_FAILED) {
munmap(p, qemu_host_page_size);
errno = EEXIST;
}
return false;
}
prot_old = prot;
@ -687,17 +691,25 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int target_prot,
/* map the middle (easier) */
if (real_start < real_last) {
void *p;
void *p, *want_p;
off_t offset1;
size_t len1;
if (flags & MAP_ANONYMOUS) {
offset1 = 0;
} else {
offset1 = offset + real_start - start;
}
p = mmap(g2h_untagged(real_start), real_last - real_start + 1,
target_to_host_prot(target_prot), flags, fd, offset1);
if (p == MAP_FAILED) {
len1 = real_last - real_start + 1;
want_p = g2h_untagged(real_start);
p = mmap(want_p, len1, target_to_host_prot(target_prot),
flags, fd, offset1);
if (p != want_p) {
if (p != MAP_FAILED) {
munmap(p, len1);
errno = EEXIST;
}
goto fail;
}
passthrough_start = real_start;