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authorHelge Deller <deller@gmx.de>2022-12-13 18:03:09 +0100
committerLaurent Vivier <laurent@vivier.eu>2023-02-03 22:55:12 +0100
commit4530deb1fe81152ae2384a56eb7edb5467f894fa (patch)
treec5a55a278ceb04cdf0fc36e44678efc59d944208
parentab6c497e7eb8a9dca45978e5118f5c67bb74ab62 (diff)
linux-user: Add emulation for MADV_WIPEONFORK and MADV_KEEPONFORK in madvise()
Both parameters have a different value on the parisc platform, so first translate the target value into a host value for usage in the native madvise() syscall. Those parameters are often used by security sensitive applications (e.g. tor browser, boringssl, ...) which expect the call to return a proper return code on failure, so return -EINVAL if qemu fails to forward the syscall to the host OS. While touching this code, enhance the comments about MADV_DONTNEED. Tested with testcase of tor browser when running hppa-linux guest on x86-64 host. Signed-off-by: Helge Deller <deller@gmx.de> Acked-by: Ilya Leoshkevich <iii@linux.ibm.com> Reviewed-by: Laurent Vivier <laurent@vivier.eu> Message-Id: <Y5iwTaydU7i66K/i@p100> Signed-off-by: Laurent Vivier <laurent@vivier.eu>
-rw-r--r--linux-user/mmap.c56
1 files changed, 43 insertions, 13 deletions
diff --git a/linux-user/mmap.c b/linux-user/mmap.c
index 10f5079331..28135c9e6a 100644
--- a/linux-user/mmap.c
+++ b/linux-user/mmap.c
@@ -857,7 +857,7 @@ abi_long target_mremap(abi_ulong old_addr, abi_ulong old_size,
return new_addr;
}
-static bool can_passthrough_madv_dontneed(abi_ulong start, abi_ulong end)
+static bool can_passthrough_madvise(abi_ulong start, abi_ulong end)
{
ulong addr;
@@ -901,23 +901,53 @@ abi_long target_madvise(abi_ulong start, abi_ulong len_in, int advice)
return -TARGET_EINVAL;
}
+ /* Translate for some architectures which have different MADV_xxx values */
+ switch (advice) {
+ case TARGET_MADV_DONTNEED: /* alpha */
+ advice = MADV_DONTNEED;
+ break;
+ case TARGET_MADV_WIPEONFORK: /* parisc */
+ advice = MADV_WIPEONFORK;
+ break;
+ case TARGET_MADV_KEEPONFORK: /* parisc */
+ advice = MADV_KEEPONFORK;
+ break;
+ /* we do not care about the other MADV_xxx values yet */
+ }
+
/*
- * A straight passthrough may not be safe because qemu sometimes turns
- * private file-backed mappings into anonymous mappings.
+ * Most advice values are hints, so ignoring and returning success is ok.
+ *
+ * However, some advice values such as MADV_DONTNEED, MADV_WIPEONFORK and
+ * MADV_KEEPONFORK are not hints and need to be emulated.
*
- * This is a hint, so ignoring and returning success is ok.
+ * A straight passthrough for those may not be safe because qemu sometimes
+ * turns private file-backed mappings into anonymous mappings.
+ * can_passthrough_madvise() helps to check if a passthrough is possible by
+ * comparing mappings that are known to have the same semantics in the host
+ * and the guest. In this case passthrough is safe.
*
- * This breaks MADV_DONTNEED, completely implementing which is quite
- * complicated. However, there is one low-hanging fruit: mappings that are
- * known to have the same semantics in the host and the guest. In this case
- * passthrough is safe, so do it.
+ * We pass through MADV_WIPEONFORK and MADV_KEEPONFORK if possible and
+ * return failure if not.
+ *
+ * MADV_DONTNEED is passed through as well, if possible.
+ * If passthrough isn't possible, we nevertheless (wrongly!) return
+ * success, which is broken but some userspace programs fail to work
+ * otherwise. Completely implementing such emulation is quite complicated
+ * though.
*/
mmap_lock();
- if (advice == TARGET_MADV_DONTNEED &&
- can_passthrough_madv_dontneed(start, end)) {
- ret = get_errno(madvise(g2h_untagged(start), len, MADV_DONTNEED));
- if (ret == 0) {
- page_reset_target_data(start, start + len);
+ switch (advice) {
+ case MADV_WIPEONFORK:
+ case MADV_KEEPONFORK:
+ ret = -EINVAL;
+ /* fall through */
+ case MADV_DONTNEED:
+ if (can_passthrough_madvise(start, end)) {
+ ret = get_errno(madvise(g2h_untagged(start), len, advice));
+ if ((advice == MADV_DONTNEED) && (ret == 0)) {
+ page_reset_target_data(start, start + len);
+ }
}
}
mmap_unlock();