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  1. 11 7月, 2006 2 次提交
  3. 03 7月, 2006 1 次提交
  5. 30 6月, 2006 1 次提交
    • C
      [AF_UNIX]: Datagram getpeersec · 877ce7c1
      由 Catherine Zhang 提交于 
      This patch implements an API whereby an application can determine the
label of its peer's Unix datagram sockets via the auxiliary data mechanism of
recvmsg.

Patch purpose:

This patch enables a security-aware application to retrieve the
security context of the peer of a Unix datagram socket.  The application
can then use this security context to determine the security context for
processing on behalf of the peer who sent the packet.

Patch design and implementation:

The design and implementation is very similar to the UDP case for INET
sockets.  Basically we build upon the existing Unix domain socket API for
retrieving user credentials.  Linux offers the API for obtaining user
credentials via ancillary messages (i.e., out of band/control messages
that are bundled together with a normal message).  To retrieve the security
context, the application first indicates to the kernel such desire by
setting the SO_PASSSEC option via getsockopt.  Then the application
retrieves the security context using the auxiliary data mechanism.

An example server application for Unix datagram socket should look like this:

toggle = 1;
toggle_len = sizeof(toggle);

setsockopt(sockfd, SOL_SOCKET, SO_PASSSEC, &toggle, &toggle_len);
recvmsg(sockfd, &msg_hdr, 0);
if (msg_hdr.msg_controllen > sizeof(struct cmsghdr)) {
    cmsg_hdr = CMSG_FIRSTHDR(&msg_hdr);
    if (cmsg_hdr->cmsg_len <= CMSG_LEN(sizeof(scontext)) &&
        cmsg_hdr->cmsg_level == SOL_SOCKET &&
        cmsg_hdr->cmsg_type == SCM_SECURITY) {
        memcpy(&scontext, CMSG_DATA(cmsg_hdr), sizeof(scontext));
    }
}

sock_setsockopt is enhanced with a new socket option SOCK_PASSSEC to allow
a server socket to receive security context of the peer.

Testing:

We have tested the patch by setting up Unix datagram client and server
applications.  We verified that the server can retrieve the security context
using the auxiliary data mechanism of recvmsg.
Signed-off-by: NCatherine Zhang <cxzhang@watson.ibm.com>
Acked-by: NAcked-by: James Morris <jmorris@namei.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      877ce7c1
  7. 23 6月, 2006 9 次提交
  9. 18 6月, 2006 1 次提交
  11. 29 4月, 2006 1 次提交
  13. 26 4月, 2006 1 次提交
  15. 11 4月, 2006 2 次提交
  17. 28 3月, 2006 3 次提交
    • I
      [PATCH] lightweight robust futexes updates · 8f17d3a5
      由 Ingo Molnar 提交于 
      - fix: initialize the robust list(s) to NULL in copy_process.

- doc update

- cleanup: rename _inuser to _inatomic

- __user cleanups and other small cleanups
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: Andi Kleen <ak@muc.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      8f17d3a5
    • I
      [PATCH] lightweight robust futexes: arch defaults · e9056f13
      由 Ingo Molnar 提交于 
      This patchset provides a new (written from scratch) implementation of robust
futexes, called "lightweight robust futexes".  We believe this new
implementation is faster and simpler than the vma-based robust futex solutions
presented before, and we'd like this patchset to be adopted in the upstream
kernel.  This is version 1 of the patchset.

  Background
  ----------

What are robust futexes?  To answer that, we first need to understand what
futexes are: normal futexes are special types of locks that in the
noncontended case can be acquired/released from userspace without having to
enter the kernel.

A futex is in essence a user-space address, e.g.  a 32-bit lock variable
field.  If userspace notices contention (the lock is already owned and someone
else wants to grab it too) then the lock is marked with a value that says
"there's a waiter pending", and the sys_futex(FUTEX_WAIT) syscall is used to
wait for the other guy to release it.  The kernel creates a 'futex queue'
internally, so that it can later on match up the waiter with the waker -
without them having to know about each other.  When the owner thread releases
the futex, it notices (via the variable value) that there were waiter(s)
pending, and does the sys_futex(FUTEX_WAKE) syscall to wake them up.  Once all
waiters have taken and released the lock, the futex is again back to
'uncontended' state, and there's no in-kernel state associated with it.  The
kernel completely forgets that there ever was a futex at that address.  This
method makes futexes very lightweight and scalable.

"Robustness" is about dealing with crashes while holding a lock: if a process
exits prematurely while holding a pthread_mutex_t lock that is also shared
with some other process (e.g.  yum segfaults while holding a pthread_mutex_t,
or yum is kill -9-ed), then waiters for that lock need to be notified that the
last owner of the lock exited in some irregular way.

To solve such types of problems, "robust mutex" userspace APIs were created:
pthread_mutex_lock() returns an error value if the owner exits prematurely -
and the new owner can decide whether the data protected by the lock can be
recovered safely.

There is a big conceptual problem with futex based mutexes though: it is the
kernel that destroys the owner task (e.g.  due to a SEGFAULT), but the kernel
cannot help with the cleanup: if there is no 'futex queue' (and in most cases
there is none, futexes being fast lightweight locks) then the kernel has no
information to clean up after the held lock!  Userspace has no chance to clean
up after the lock either - userspace is the one that crashes, so it has no
opportunity to clean up.  Catch-22.

In practice, when e.g.  yum is kill -9-ed (or segfaults), a system reboot is
needed to release that futex based lock.  This is one of the leading
bugreports against yum.

To solve this problem, 'Robust Futex' patches were created and presented on
lkml: the one written by Todd Kneisel and David Singleton is the most advanced
at the moment.  These patches all tried to extend the futex abstraction by
registering futex-based locks in the kernel - and thus give the kernel a
chance to clean up.

E.g.  in David Singleton's robust-futex-6.patch, there are 3 new syscall
variants to sys_futex(): FUTEX_REGISTER, FUTEX_DEREGISTER and FUTEX_RECOVER.
The kernel attaches such robust futexes to vmas (via
vma->vm_file->f_mapping->robust_head), and at do_exit() time, all vmas are
searched to see whether they have a robust_head set.

Lots of work went into the vma-based robust-futex patch, and recently it has
improved significantly, but unfortunately it still has two fundamental
problems left:

 - they have quite complex locking and race scenarios.  The vma-based
   patches had been pending for years, but they are still not completely
   reliable.

 - they have to scan _every_ vma at sys_exit() time, per thread!

The second disadvantage is a real killer: pthread_exit() takes around 1
microsecond on Linux, but with thousands (or tens of thousands) of vmas every
pthread_exit() takes a millisecond or more, also totally destroying the CPU's
L1 and L2 caches!

This is very much noticeable even for normal process sys_exit_group() calls:
the kernel has to do the vma scanning unconditionally!  (this is because the
kernel has no knowledge about how many robust futexes there are to be cleaned
up, because a robust futex might have been registered in another task, and the
futex variable might have been simply mmap()-ed into this process's address
space).

This huge overhead forced the creation of CONFIG_FUTEX_ROBUST, but worse than
that: the overhead makes robust futexes impractical for any type of generic
Linux distribution.

So it became clear to us, something had to be done.  Last week, when Thomas
Gleixner tried to fix up the vma-based robust futex patch in the -rt tree, he
found a handful of new races and we were talking about it and were analyzing
the situation.  At that point a fundamentally different solution occured to
me.  This patchset (written in the past couple of days) implements that new
solution.  Be warned though - the patchset does things we normally dont do in
Linux, so some might find the approach disturbing.  Parental advice
recommended ;-)

  New approach to robust futexes
  ------------------------------

At the heart of this new approach there is a per-thread private list of robust
locks that userspace is holding (maintained by glibc) - which userspace list
is registered with the kernel via a new syscall [this registration happens at
most once per thread lifetime].  At do_exit() time, the kernel checks this
user-space list: are there any robust futex locks to be cleaned up?

In the common case, at do_exit() time, there is no list registered, so the
cost of robust futexes is just a simple current->robust_list != NULL
comparison.  If the thread has registered a list, then normally the list is
empty.  If the thread/process crashed or terminated in some incorrect way then
the list might be non-empty: in this case the kernel carefully walks the list
[not trusting it], and marks all locks that are owned by this thread with the
FUTEX_OWNER_DEAD bit, and wakes up one waiter (if any).

The list is guaranteed to be private and per-thread, so it's lockless.  There
is one race possible though: since adding to and removing from the list is
done after the futex is acquired by glibc, there is a few instructions window
for the thread (or process) to die there, leaving the futex hung.  To protect
against this possibility, userspace (glibc) also maintains a simple per-thread
'list_op_pending' field, to allow the kernel to clean up if the thread dies
after acquiring the lock, but just before it could have added itself to the
list.  Glibc sets this list_op_pending field before it tries to acquire the
futex, and clears it after the list-add (or list-remove) has finished.

That's all that is needed - all the rest of robust-futex cleanup is done in
userspace [just like with the previous patches].

Ulrich Drepper has implemented the necessary glibc support for this new
mechanism, which fully enables robust mutexes.  (Ulrich plans to commit these
changes to glibc-HEAD later today.)

Key differences of this userspace-list based approach, compared to the vma
based method:

 - it's much, much faster: at thread exit time, there's no need to loop
   over every vma (!), which the VM-based method has to do.  Only a very
   simple 'is the list empty' op is done.

 - no VM changes are needed - 'struct address_space' is left alone.

 - no registration of individual locks is needed: robust mutexes dont need
   any extra per-lock syscalls.  Robust mutexes thus become a very lightweight
   primitive - so they dont force the application designer to do a hard choice
   between performance and robustness - robust mutexes are just as fast.

 - no per-lock kernel allocation happens.

 - no resource limits are needed.

 - no kernel-space recovery call (FUTEX_RECOVER) is needed.

 - the implementation and the locking is "obvious", and there are no
   interactions with the VM.

  Performance
  -----------

I have benchmarked the time needed for the kernel to process a list of 1
million (!) held locks, using the new method [on a 2GHz CPU]:

 - with FUTEX_WAIT set [contended mutex]: 130 msecs
 - without FUTEX_WAIT set [uncontended mutex]: 30 msecs

I have also measured an approach where glibc does the lock notification [which
it currently does for !pshared robust mutexes], and that took 256 msecs -
clearly slower, due to the 1 million FUTEX_WAKE syscalls userspace had to do.

(1 million held locks are unheard of - we expect at most a handful of locks to
be held at a time.  Nevertheless it's nice to know that this approach scales
nicely.)

  Implementation details
  ----------------------

The patch adds two new syscalls: one to register the userspace list, and one
to query the registered list pointer:

 asmlinkage long
 sys_set_robust_list(struct robust_list_head __user *head,
                     size_t len);

 asmlinkage long
 sys_get_robust_list(int pid, struct robust_list_head __user **head_ptr,
                     size_t __user *len_ptr);

List registration is very fast: the pointer is simply stored in
current->robust_list.  [Note that in the future, if robust futexes become
widespread, we could extend sys_clone() to register a robust-list head for new
threads, without the need of another syscall.]

So there is virtually zero overhead for tasks not using robust futexes, and
even for robust futex users, there is only one extra syscall per thread
lifetime, and the cleanup operation, if it happens, is fast and
straightforward.  The kernel doesnt have any internal distinction between
robust and normal futexes.

If a futex is found to be held at exit time, the kernel sets the highest bit
of the futex word:

	#define FUTEX_OWNER_DIED        0x40000000

and wakes up the next futex waiter (if any). User-space does the rest of
the cleanup.

Otherwise, robust futexes are acquired by glibc by putting the TID into the
futex field atomically.  Waiters set the FUTEX_WAITERS bit:

	#define FUTEX_WAITERS           0x80000000

and the remaining bits are for the TID.

  Testing, architecture support
  -----------------------------

I've tested the new syscalls on x86 and x86_64, and have made sure the parsing
of the userspace list is robust [ ;-) ] even if the list is deliberately
corrupted.

i386 and x86_64 syscalls are wired up at the moment, and Ulrich has tested the
new glibc code (on x86_64 and i386), and it works for his robust-mutex
testcases.

All other architectures should build just fine too - but they wont have the
new syscalls yet.

Architectures need to implement the new futex_atomic_cmpxchg_inuser() inline
function before writing up the syscalls (that function returns -ENOSYS right
now).

This patch:

Add placeholder futex_atomic_cmpxchg_inuser() implementations to every
architecture that supports futexes.  It returns -ENOSYS.
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NArjan van de Ven <arjan@infradead.org>
Acked-by: NUlrich Drepper <drepper@redhat.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      e9056f13
    • K
      [PATCH] unify pfn_to_page: FRV pfn_to_page · 5cdac7ca
      由 KAMEZAWA Hiroyuki 提交于 
      FRV can use generic funcs.
Signed-off-by: NKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      5cdac7ca
  19. 27 3月, 2006 2 次提交
  21. 26 3月, 2006 1 次提交
    • D
      [PATCH] POLLRDHUP/EPOLLRDHUP handling for half-closed devices notifications · f348d70a
      由 Davide Libenzi 提交于 
      Implement the half-closed devices notifiation, by adding a new POLLRDHUP
(and its alias EPOLLRDHUP) bit to the existing poll/select sets.  Since the
existing POLLHUP handling, that does not report correctly half-closed
devices, was feared to be changed, this implementation leaves the current
POLLHUP reporting unchanged and simply add a new bit that is set in the few
places where it makes sense.  The same thing was discussed and conceptually
agreed quite some time ago:

http://lkml.org/lkml/2003/7/12/116

Since this new event bit is added to the existing Linux poll infrastruture,
even the existing poll/select system calls will be able to use it.  As far
as the existing POLLHUP handling, the patch leaves it as is.  The
pollrdhup-2.6.16.rc5-0.10.diff defines the POLLRDHUP for all the existing
archs and sets the bit in the six relevant files.  The other attached diff
is the simple change required to sys/epoll.h to add the EPOLLRDHUP
definition.

There is "a stupid program" to test POLLRDHUP delivery here:

 http://www.xmailserver.org/pollrdhup-test.c

It tests poll(2), but since the delivery is same epoll(2) will work equally.
Signed-off-by: NDavide Libenzi <davidel@xmailserver.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      f348d70a
  23. 16 2月, 2006 1 次提交
  25. 15 2月, 2006 3 次提交
    • D
      [PATCH] FRV: Use virtual interrupt disablement · 28baebae
      由 David Howells 提交于 
      Make the FRV arch use virtual interrupt disablement because accesses to the
processor status register (PSR) are relatively slow and because we will
soon have the need to deal with multiple interrupt controls at the same
time (separate h/w and inter-core interrupts).

The way this is done is to dedicate one of the four integer condition code
registers (ICC2) to maintaining a virtual interrupt disablement state
whilst inside the kernel.  This uses the ICC2.Z flag (Zero) to indicate
whether the interrupts are virtually disabled and the ICC2.C flag (Carry)
to indicate whether the interrupts are physically disabled.

ICC2.Z is set to indicate interrupts are virtually disabled.  ICC2.C is set
to indicate interrupts are physically enabled.  Under normal running
conditions Z==0 and C==1.

Disabling interrupts with local_irq_disable() doesn't then actually
physically disable interrupts - it merely sets ICC2.Z to 1.  Should an
interrupt then happen, the exception prologue will note ICC2.Z is set and
branch out of line using one instruction (an unlikely BEQ).  Here it will
physically disable interrupts and clear ICC2.C.

When it comes time to enable interrupts (local_irq_enable()), this simply
clears the ICC2.Z flag and invokes a trap #2 if both Z and C flags are
clear (the HI integer condition).  This can be done with the TIHI
conditional trap instruction.

The trap then physically reenables interrupts and sets ICC2.C again.  Upon
returning the interrupt will be taken as interrupts will then be enabled.
Note that whilst processing the trap, the whole exceptions system is
disabled, and so an interrupt can't happen till it returns.

If no pending interrupt had happened, ICC2.C would still be set, the HI
condition would not be fulfilled, and no trap will happen.

Saving interrupts (local_irq_save) is simply a matter of pulling the ICC2.Z
flag out of the CCR register, shifting it down and masking it off.  This
gives a result of 0 if interrupts were enabled and 1 if they weren't.

Restoring interrupts (local_irq_restore) is then a matter of taking the
saved value mentioned previously and XOR'ing it against 1.  If it was one,
the result will be zero, and if it was zero the result will be non-zero.
This result is then used to affect the ICC2.Z flag directly (it is a
condition code flag after all).  An XOR instruction does not affect the
Carry flag, and so that bit of state is unchanged.  The two flags can then
be sampled to see if they're both zero using the trap (TIHI) as for the
unconditional reenablement (local_irq_enable).

This patch also:

 (1) Modifies the debugging stub (break.S) to handle single-stepping crossing
     into the trap #2 handler and into virtually disabled interrupts.

 (2) Removes superseded fixup pointers from the second instructions in the trap
     tables (there's no a separate fixup table for this).

 (3) Declares the trap #3 vector for use in .org directives in the trap table.

 (4) Moves irq_enter() and irq_exit() in do_IRQ() to avoid problems with
     virtual interrupt handling, and removes the duplicate code that has now
     been folded into irq_exit() (softirq and preemption handling).

 (5) Tells the compiler in the arch Makefile that ICC2 is now reserved.

 (6) Documents the in-kernel ABI, including the virtual interrupts.

 (7) Renames the old irq management functions to different names.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      28baebae
    • D
      [PATCH] FRV: Miscellaneous fixes · 68f624fc
      由 David Howells 提交于 
      Make various alterations and fixes to the FRV arch:

 (1) Resyncs the FRV system call collection with the i386 arch.

 (2) Discards __iounmap() as it's not used.

 (3) Fixes the use of the SWAP/SWAPI instruction to get the arguments the right
     way around in atomic.h, and also to get the asm constraints correct.

 (4) Moves copy_to/from_user_page() to asm/cacheflush.h to be consistent with
     other archs.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      68f624fc
    • M
      [PATCH] madvise MADV_DONTFORK/MADV_DOFORK · f8225661
      由 Michael S. Tsirkin 提交于 
      Currently, copy-on-write may change the physical address of a page even if the
user requested that the page is pinned in memory (either by mlock or by
get_user_pages).  This happens if the process forks meanwhile, and the parent
writes to that page.  As a result, the page is orphaned: in case of
get_user_pages, the application will never see any data hardware DMA's into
this page after the COW.  In case of mlock'd memory, the parent is not getting
the realtime/security benefits of mlock.

In particular, this affects the Infiniband modules which do DMA from and into
user pages all the time.

This patch adds madvise options to control whether memory range is inherited
across fork.  Useful e.g.  for when hardware is doing DMA from/into these
pages.  Could also be useful to an application wanting to speed up its forks
by cutting large areas out of consideration.
Signed-off-by: NMichael S. Tsirkin <mst@mellanox.co.il>
Acked-by: NHugh Dickins <hugh@veritas.com>
Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      f8225661
  27. 04 2月, 2006 1 次提交
  29. 19 1月, 2006 1 次提交
    • D
      [PATCH] Handle TIF_RESTORE_SIGMASK for FRV · a411aee9
      由 David Howells 提交于 
      Handle TIF_RESTORE_SIGMASK as added by David Woodhouse's patch entitled:

        [PATCH] 2/3 Add TIF_RESTORE_SIGMASK support for arch/powerpc
        [PATCH] 3/3 Generic sys_rt_sigsuspend

It does the following:

 (1) Declares TIF_RESTORE_SIGMASK for FRV.

 (2) Invokes it over to do_signal() when TIF_RESTORE_SIGMASK is set.

 (3) Makes do_signal() support TIF_RESTORE_SIGMASK, using the signal mask saved
     in current->saved_sigmask.

 (4) Discards sys_rt_sigsuspend() from the arch, using the generic one instead.

 (5) Makes sys_sigsuspend() save the signal mask and set TIF_RESTORE_SIGMASK
     rather than attempting to fudge the return registers.

 (6) Makes sys_sigsuspend() return -ERESTARTNOHAND rather than looping
     intrinsically.

 (7) Makes setup_frame(), setup_rt_frame() and handle_signal() return 0 or
     -EFAULT rather than true/false to be consistent with the rest of the
      kernel.

Due to the fact do_signal() is then only called from one place:

 (8) Make do_signal() no longer have a return value is it was just being
     ignored; force_sig() takes care of this.

 (9) Discards the old sigmask argument to do_signal() as it's no longer
     necessary.

This patch depends on the FRV signalling patches as well as the
sys_rt_sigsuspend patch.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NDavid Woodhouse <dwmw2@infradead.org>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>
      a411aee9
  31. 13 1月, 2006 1 次提交
  33. 11 1月, 2006 1 次提交
  35. 10 1月, 2006 2 次提交
  37. 09 1月, 2006 5 次提交
  39. 07 1月, 2006 1 次提交