[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[PULL 18/22] linux-user: Add emulation for MADV_WIPEONFORK and MADV_KEEP
From: |
Laurent Vivier |
Subject: |
[PULL 18/22] linux-user: Add emulation for MADV_WIPEONFORK and MADV_KEEPONFORK in madvise() |
Date: |
Sat, 4 Feb 2023 17:08:26 +0100 |
From: Helge Deller <deller@gmx.de>
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>
---
linux-user/mmap.c | 56 ++++++++++++++++++++++++++++++++++++-----------
1 file changed, 43 insertions(+), 13 deletions(-)
diff --git a/linux-user/mmap.c b/linux-user/mmap.c
index 10f5079331c3..28135c9e6aa9 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();
--
2.39.1
- [PULL 17/22] linux-user: Improve strace output of personality() and sysinfo(), (continued)
- [PULL 17/22] linux-user: Improve strace output of personality() and sysinfo(), Laurent Vivier, 2023/02/04
- [PULL 15/22] linux-user: Fix SO_ERROR return code of getsockopt(), Laurent Vivier, 2023/02/04
- [PULL 11/22] Revert "linux-user: fix compat with glibc >= 2.36 sys/mount.h", Laurent Vivier, 2023/02/04
- [PULL 19/22] linux-user: Show 4th argument of rt_sigprocmask() in strace, Laurent Vivier, 2023/02/04
- [PULL 22/22] linux-user: Allow sendmsg() without IOV, Laurent Vivier, 2023/02/04
- [PULL 20/22] linux-user: Enhance strace output for various syscalls, Laurent Vivier, 2023/02/04
- [PULL 09/22] linux-user: add more netlink protocol constants, Laurent Vivier, 2023/02/04
- [PULL 03/22] linux-user/strace: Add output for execveat() syscall, Laurent Vivier, 2023/02/04
- [PULL 04/22] linux-user/syscall: Extract do_execve() from do_syscall1(), Laurent Vivier, 2023/02/04
- [PULL 05/22] linux-user/syscall: Implement execveat(), Laurent Vivier, 2023/02/04
- [PULL 18/22] linux-user: Add emulation for MADV_WIPEONFORK and MADV_KEEPONFORK in madvise(),
Laurent Vivier <=
- [PULL 16/22] linux-user: Fix /proc/cpuinfo output for hppa, Laurent Vivier, 2023/02/04
- [PULL 13/22] linux-user: Improve strace output of getgroups() and setgroups(), Laurent Vivier, 2023/02/04
- [PULL 21/22] linux-user: Implement SOL_ALG encryption support, Laurent Vivier, 2023/02/04
- [PULL 08/22] linux-user: fix strace build w/out munlockall, Laurent Vivier, 2023/02/04
- [PULL 14/22] linux-user: move target_flat.h to target subdirs, Laurent Vivier, 2023/02/04
- [PULL 12/22] linux-user: Add strace output for clock_getres_time64() and futex_time64(), Laurent Vivier, 2023/02/04
- Re: [PULL 00/22] Linux user for 8.0 patches, Peter Maydell, 2023/02/04