[Bug 1875702] [NEW] madvise reports success, but doesn't implement WIPEONFORK.

[Bug 1875702] [NEW] madvise reports success, but doesn't implement WIPEONFORK.

[agl]

Public bug reported:

The implementation of madvise (linux-user/syscall.c:11331, tag
v5.0.0-rc4) always returns zero (i.e. success). However, an application
requesting (at least) MADV_WIPEONFORK may need to know whether the call
was actually successful. If not (because the kernel doesn't support
WIPEONFORK) then it will need to take other measures to provide fork-
safety (such as drawing entropy from the kernel in every case). But, if
the application believes that WIPEONFORK is supported (because madvise
returned zero), but it actually isn't (as in qemu), then it may forego
those protections on the assumption that WIPEONFORK will provide fork-
safety.

Roughly, the comment in qemu that says "This is a hint, so ignoring and
returning success is ok." is no longer accurate in the presence of
MADV_WIPEONFORK.

(This is not purely academic: BoringSSL is planning on acting in this
way. We found the qemu behaviour in pre-release testing and are planning
on making an madvise call with advice=-1 first to test whether unknown
advice values actually produce EINVAL.)

** Affects: qemu
     Importance: Undecided
         Status: New

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Title:
  madvise reports success, but doesn't implement WIPEONFORK.

Status in QEMU:
  New

Bug description:
  The implementation of madvise (linux-user/syscall.c:11331, tag
  v5.0.0-rc4) always returns zero (i.e. success). However, an
  application requesting (at least) MADV_WIPEONFORK may need to know
  whether the call was actually successful. If not (because the kernel
  doesn't support WIPEONFORK) then it will need to take other measures
  to provide fork-safety (such as drawing entropy from the kernel in
  every case). But, if the application believes that WIPEONFORK is
  supported (because madvise returned zero), but it actually isn't (as
  in qemu), then it may forego those protections on the assumption that
  WIPEONFORK will provide fork-safety.

  Roughly, the comment in qemu that says "This is a hint, so ignoring
  and returning success is ok." is no longer accurate in the presence of
  MADV_WIPEONFORK.

  (This is not purely academic: BoringSSL is planning on acting in this
  way. We found the qemu behaviour in pre-release testing and are
  planning on making an madvise call with advice=-1 first to test
  whether unknown advice values actually produce EINVAL.)

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[Bug 1875702] Re: madvise reports success, but doesn't implement WIPEONFORK.

[Laurent Vivier]

** Changed in: qemu
     Assignee: (unassigned) => Laurent Vivier (laurent-vivier)

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Title:
  madvise reports success, but doesn't implement WIPEONFORK.

Status in QEMU:
  New

Bug description:
  The implementation of madvise (linux-user/syscall.c:11331, tag
  v5.0.0-rc4) always returns zero (i.e. success). However, an
  application requesting (at least) MADV_WIPEONFORK may need to know
  whether the call was actually successful. If not (because the kernel
  doesn't support WIPEONFORK) then it will need to take other measures
  to provide fork-safety (such as drawing entropy from the kernel in
  every case). But, if the application believes that WIPEONFORK is
  supported (because madvise returned zero), but it actually isn't (as
  in qemu), then it may forego those protections on the assumption that
  WIPEONFORK will provide fork-safety.

  Roughly, the comment in qemu that says "This is a hint, so ignoring
  and returning success is ok." is no longer accurate in the presence of
  MADV_WIPEONFORK.

  (This is not purely academic: BoringSSL is planning on acting in this
  way. We found the qemu behaviour in pre-release testing and are
  planning on making an madvise call with advice=-1 first to test
  whether unknown advice values actually produce EINVAL.)

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[Bug 1875702] Re: madvise reports success, but doesn't implement WIPEONFORK.

[Thomas Huth]

The QEMU project is currently moving its bug tracking to another system.
For this we need to know which bugs are still valid and which could be
closed already. Thus we are setting older bugs to "Incomplete" now.

If you still think this bug report here is valid, then please switch
the state back to "New" within the next 60 days, otherwise this report
will be marked as "Expired". Or please mark it as "Fix Released" if
the problem has been solved with a newer version of QEMU already.

Thank you and sorry for the inconvenience.


** Changed in: qemu
       Status: New => Incomplete

** Tags added: linux-user

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Title:
  madvise reports success, but doesn't implement WIPEONFORK.

Status in QEMU:
  Incomplete

Bug description:
  The implementation of madvise (linux-user/syscall.c:11331, tag
  v5.0.0-rc4) always returns zero (i.e. success). However, an
  application requesting (at least) MADV_WIPEONFORK may need to know
  whether the call was actually successful. If not (because the kernel
  doesn't support WIPEONFORK) then it will need to take other measures
  to provide fork-safety (such as drawing entropy from the kernel in
  every case). But, if the application believes that WIPEONFORK is
  supported (because madvise returned zero), but it actually isn't (as
  in qemu), then it may forego those protections on the assumption that
  WIPEONFORK will provide fork-safety.

  Roughly, the comment in qemu that says "This is a hint, so ignoring
  and returning success is ok." is no longer accurate in the presence of
  MADV_WIPEONFORK.

  (This is not purely academic: BoringSSL is planning on acting in this
  way. We found the qemu behaviour in pre-release testing and are
  planning on making an madvise call with advice=-1 first to test
  whether unknown advice values actually produce EINVAL.)

To manage notifications about this bug go to:
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[Bug 1875702] Re: madvise reports success, but doesn't implement WIPEONFORK.

[Peter Maydell]

Still relevant. See also bug #1926521 -- MADV_DONTNEED is another
madvise() value that can't be ignored as "just a hint".


** Changed in: qemu
       Status: Incomplete => Confirmed

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https://bugs.launchpad.net/bugs/1875702

Title:
  madvise reports success, but doesn't implement WIPEONFORK.

Status in QEMU:
  Confirmed

Bug description:
  The implementation of madvise (linux-user/syscall.c:11331, tag
  v5.0.0-rc4) always returns zero (i.e. success). However, an
  application requesting (at least) MADV_WIPEONFORK may need to know
  whether the call was actually successful. If not (because the kernel
  doesn't support WIPEONFORK) then it will need to take other measures
  to provide fork-safety (such as drawing entropy from the kernel in
  every case). But, if the application believes that WIPEONFORK is
  supported (because madvise returned zero), but it actually isn't (as
  in qemu), then it may forego those protections on the assumption that
  WIPEONFORK will provide fork-safety.

  Roughly, the comment in qemu that says "This is a hint, so ignoring
  and returning success is ok." is no longer accurate in the presence of
  MADV_WIPEONFORK.

  (This is not purely academic: BoringSSL is planning on acting in this
  way. We found the qemu behaviour in pre-release testing and are
  planning on making an madvise call with advice=-1 first to test
  whether unknown advice values actually produce EINVAL.)

To manage notifications about this bug go to:
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[Bug 1875702] Re: madvise reports success, but doesn't implement WIPEONFORK.

[Thomas Huth]

This is an automated cleanup. This bug report has been moved to QEMU's
new bug tracker on gitlab.com and thus gets marked as 'expired' now.
Please continue with the discussion here:

 https://gitlab.com/qemu-project/qemu/-/issues/343


** Changed in: qemu
       Status: Confirmed => Expired

** Changed in: qemu
     Assignee: Laurent Vivier (laurent-vivier) => (unassigned)

** Bug watch added: gitlab.com/qemu-project/qemu/-/issues #343
   https://gitlab.com/qemu-project/qemu/-/issues/343

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1875702

Title:
  madvise reports success, but doesn't implement WIPEONFORK.

Status in QEMU:
  Expired

Bug description:
  The implementation of madvise (linux-user/syscall.c:11331, tag
  v5.0.0-rc4) always returns zero (i.e. success). However, an
  application requesting (at least) MADV_WIPEONFORK may need to know
  whether the call was actually successful. If not (because the kernel
  doesn't support WIPEONFORK) then it will need to take other measures
  to provide fork-safety (such as drawing entropy from the kernel in
  every case). But, if the application believes that WIPEONFORK is
  supported (because madvise returned zero), but it actually isn't (as
  in qemu), then it may forego those protections on the assumption that
  WIPEONFORK will provide fork-safety.

  Roughly, the comment in qemu that says "This is a hint, so ignoring
  and returning success is ok." is no longer accurate in the presence of
  MADV_WIPEONFORK.

  (This is not purely academic: BoringSSL is planning on acting in this
  way. We found the qemu behaviour in pre-release testing and are
  planning on making an madvise call with advice=-1 first to test
  whether unknown advice values actually produce EINVAL.)

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1875702/+subscriptions