linux-stable.git/kernel, branch v4.9.151

mm, devm_memremap_pages: kill mapping "System RAM" support

2019-01-13T09:03:51+00:00

commit 06489cfbd915ff36c8e36df27f1c2dc60f97ca56 upstream.

Given the fact that devm_memremap_pages() requires a percpu_ref that is
torn down by devm_memremap_pages_release() the current support for mapping
RAM is broken.

Support for remapping "System RAM" has been broken since the beginning and
there is no existing user of this this code path, so just kill the support
and make it an explicit error.

This cleanup also simplifies a follow-on patch to fix the error path when
setting a devm release action for devm_memremap_pages_release() fails.

Link: http://lkml.kernel.org/r/154275557997.76910.14689813630968180480.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams 
Reviewed-by: "Jérôme Glisse" 
Reviewed-by: Christoph Hellwig 
Reviewed-by: Logan Gunthorpe 
Cc: Balbir Singh 
Cc: Michal Hocko 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

mm, devm_memremap_pages: mark devm_memremap_pages() EXPORT_SYMBOL_GPL

2019-01-13T09:03:51+00:00

commit 808153e1187fa77ac7d7dad261ff476888dcf398 upstream.

devm_memremap_pages() is a facility that can create struct page entries
for any arbitrary range and give drivers the ability to subvert core
aspects of page management.

Specifically the facility is tightly integrated with the kernel's memory
hotplug functionality.  It injects an altmap argument deep into the
architecture specific vmemmap implementation to allow allocating from
specific reserved pages, and it has Linux specific assumptions about page
structure reference counting relative to get_user_pages() and
get_user_pages_fast().  It was an oversight and a mistake that this was
not marked EXPORT_SYMBOL_GPL from the outset.

Again, devm_memremap_pagex() exposes and relies upon core kernel internal
assumptions and will continue to evolve along with 'struct page', memory
hotplug, and support for new memory types / topologies.  Only an in-kernel
GPL-only driver is expected to keep up with this ongoing evolution.  This
interface, and functionality derived from this interface, is not suitable
for kernel-external drivers.

Link: http://lkml.kernel.org/r/154275557457.76910.16923571232582744134.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams 
Reviewed-by: Christoph Hellwig 
Acked-by: Michal Hocko 
Cc: "Jérôme Glisse" 
Cc: Balbir Singh 
Cc: Logan Gunthorpe 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

fork: record start_time late

2019-01-13T09:03:51+00:00

commit 7b55851367136b1efd84d98fea81ba57a98304cf upstream.

This changes the fork(2) syscall to record the process start_time after
initializing the basic task structure but still before making the new
process visible to user-space.

Technically, we could record the start_time anytime during fork(2).  But
this might lead to scenarios where a start_time is recorded long before
a process becomes visible to user-space.  For instance, with
userfaultfd(2) and TLS, user-space can delay the execution of fork(2)
for an indefinite amount of time (and will, if this causes network
access, or similar).

By recording the start_time late, it much closer reflects the point in
time where the process becomes live and can be observed by other
processes.

Lastly, this makes it much harder for user-space to predict and control
the start_time they get assigned.  Previously, user-space could fork a
process and stall it in copy_thread_tls() before its pid is allocated,
but after its start_time is recorded.  This can be misused to later-on
cycle through PIDs and resume the stalled fork(2) yielding a process
that has the same pid and start_time as a process that existed before.
This can be used to circumvent security systems that identify processes
by their pid+start_time combination.

Even though user-space was always aware that start_time recording is
flaky (but several projects are known to still rely on start_time-based
identification), changing the start_time to be recorded late will help
mitigate existing attacks and make it much harder for user-space to
control the start_time a process gets assigned.

Reported-by: Jann Horn 
Signed-off-by: Tom Gundersen 
Signed-off-by: David Herrmann 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

panic: avoid deadlocks in re-entrant console drivers

2018-12-29T12:40:16+00:00

commit c7c3f05e341a9a2bd1a92993d4f996cfd6e7348e upstream.

From printk()/serial console point of view panic() is special, because
it may force CPU to re-enter printk() or/and serial console driver.
Therefore, some of serial consoles drivers are re-entrant. E.g. 8250:

serial8250_console_write()
{
	if (port->sysrq)
		locked = 0;
	else if (oops_in_progress)
		locked = spin_trylock_irqsave(&port->lock, flags);
	else
		spin_lock_irqsave(&port->lock, flags);
	...
}

panic() does set oops_in_progress via bust_spinlocks(1), so in theory
we should be able to re-enter serial console driver from panic():

	CPU0
	
	uart_console_write()
	serial8250_console_write()		// if (oops_in_progress)
						//    spin_trylock_irqsave()
	call_console_drivers()
	console_unlock()
	console_flush_on_panic()
	bust_spinlocks(1)			// oops_in_progress++
	panic()
	
	spin_lock_irqsave(&port->lock, flags)   // spin_lock_irqsave()
	serial8250_console_write()
	call_console_drivers()
	console_unlock()
	printk()
	...

However, this does not happen and we deadlock in serial console on
port->lock spinlock. And the problem is that console_flush_on_panic()
called after bust_spinlocks(0):

void panic(const char *fmt, ...)
{
	bust_spinlocks(1);
	...
	bust_spinlocks(0);
	console_flush_on_panic();
	...
}

bust_spinlocks(0) decrements oops_in_progress, so oops_in_progress
can go back to zero. Thus even re-entrant console drivers will simply
spin on port->lock spinlock. Given that port->lock may already be
locked either by a stopped CPU, or by the very same CPU we execute
panic() on (for instance, NMI panic() on printing CPU) the system
deadlocks and does not reboot.

Fix this by removing bust_spinlocks(0), so oops_in_progress is always
set in panic() now and, thus, re-entrant console drivers will trylock
the port->lock instead of spinning on it forever, when we call them
from console_flush_on_panic().

Link: http://lkml.kernel.org/r/20181025101036.6823-1-sergey.senozhatsky@gmail.com
Cc: Steven Rostedt 
Cc: Daniel Wang 
Cc: Peter Zijlstra 
Cc: Andrew Morton 
Cc: Linus Torvalds 
Cc: Greg Kroah-Hartman 
Cc: Alan Cox 
Cc: Jiri Slaby 
Cc: Peter Feiner 
Cc: linux-serial@vger.kernel.org
Cc: Sergey Senozhatsky 
Cc: stable@vger.kernel.org
Signed-off-by: Sergey Senozhatsky 
Signed-off-by: Petr Mladek 
Signed-off-by: Greg Kroah-Hartman

bpf: check pending signals while verifying programs

2018-12-21T13:11:38+00:00

[ Upstream commit c3494801cd1785e2c25f1a5735fa19ddcf9665da ]

Malicious user space may try to force the verifier to use as much cpu
time and memory as possible. Hence check for pending signals
while verifying the program.
Note that suspend of sys_bpf(PROG_LOAD) syscall will lead to EAGAIN,
since the kernel has to release the resources used for program verification.

Reported-by: Anatoly Trosinenko 
Signed-off-by: Alexei Starovoitov 
Acked-by: Daniel Borkmann 
Acked-by: Edward Cree 
Signed-off-by: Daniel Borkmann 
Signed-off-by: Sasha Levin

locking/qspinlock, x86: Provide liveness guarantee

2018-12-21T13:11:34+00:00

commit 7aa54be2976550f17c11a1c3e3630002dea39303 upstream.

On x86 we cannot do fetch_or() with a single instruction and thus end up
using a cmpxchg loop, this reduces determinism. Replace the fetch_or()
with a composite operation: tas-pending + load.

Using two instructions of course opens a window we previously did not
have. Consider the scenario:

	CPU0		CPU1		CPU2

 1)	lock
	  trylock -> (0,0,1)

 2)			lock
			  trylock /* fail */

 3)	unlock -> (0,0,0)

 4)					lock
					  trylock -> (0,0,1)

 5)			  tas-pending -> (0,1,1)
			  load-val <- (0,1,0) from 3

 6)			  clear-pending-set-locked -> (0,0,1)

			  FAIL: _2_ owners

where 5) is our new composite operation. When we consider each part of
the qspinlock state as a separate variable (as we can when
_Q_PENDING_BITS == 8) then the above is entirely possible, because
tas-pending will only RmW the pending byte, so the later load is able
to observe prior tail and lock state (but not earlier than its own
trylock, which operates on the whole word, due to coherence).

To avoid this we need 2 things:

 - the load must come after the tas-pending (obviously, otherwise it
   can trivially observe prior state).

 - the tas-pending must be a full word RmW instruction, it cannot be an XCHGB for
   example, such that we cannot observe other state prior to setting
   pending.

On x86 we can realize this by using "LOCK BTS m32, r32" for
tas-pending followed by a regular load.

Note that observing later state is not a problem:

 - if we fail to observe a later unlock, we'll simply spin-wait for
   that store to become visible.

 - if we observe a later xchg_tail(), there is no difference from that
   xchg_tail() having taken place before the tas-pending.

Suggested-by: Will Deacon 
Reported-by: Thomas Gleixner 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Will Deacon 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: andrea.parri@amarulasolutions.com
Cc: longman@redhat.com
Fixes: 59fb586b4a07 ("locking/qspinlock: Remove unbounded cmpxchg() loop from locking slowpath")
Link: https://lkml.kernel.org/r/20181003130957.183726335@infradead.org
Signed-off-by: Ingo Molnar 
[bigeasy: GEN_BINARY_RMWcc macro redo]
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Sasha Levin

locking/qspinlock: Re-order code

2018-12-21T13:11:34+00:00

commit 53bf57fab7321fb42b703056a4c80fc9d986d170 upstream.

Flip the branch condition after atomic_fetch_or_acquire(_Q_PENDING_VAL)
such that we loose the indent. This also result in a more natural code
flow IMO.

Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Will Deacon 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: andrea.parri@amarulasolutions.com
Cc: longman@redhat.com
Link: https://lkml.kernel.org/r/20181003130257.156322446@infradead.org
Signed-off-by: Ingo Molnar 
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Sasha Levin

locking/qspinlock: Kill cmpxchg() loop when claiming lock from head of queue

2018-12-21T13:11:34+00:00

commit c61da58d8a9ba9238250a548f00826eaf44af0f7 upstream.

When a queued locker reaches the head of the queue, it claims the lock
by setting _Q_LOCKED_VAL in the lockword. If there isn't contention, it
must also clear the tail as part of this operation so that subsequent
lockers can avoid taking the slowpath altogether.

Currently this is expressed as a cmpxchg() loop that practically only
runs up to two iterations. This is confusing to the reader and unhelpful
to the compiler. Rewrite the cmpxchg() loop without the loop, so that a
failed cmpxchg() implies that there is contention and we just need to
write to _Q_LOCKED_VAL without considering the rest of the lockword.

Signed-off-by: Will Deacon 
Acked-by: Peter Zijlstra (Intel) 
Acked-by: Waiman Long 
Cc: Linus Torvalds 
Cc: Thomas Gleixner 
Cc: boqun.feng@gmail.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1524738868-31318-7-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Sasha Levin

locking/qspinlock: Remove duplicate clear_pending() function from PV code

2018-12-21T13:11:34+00:00

commit 3bea9adc96842b8a7345c7fb202c16ae9c8d5b25 upstream.

The native clear_pending() function is identical to the PV version, so the
latter can simply be removed.

This fixes the build for systems with >= 16K CPUs using the PV lock implementation.

Reported-by: Waiman Long 
Signed-off-by: Will Deacon 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: boqun.feng@gmail.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/20180427101619.GB21705@arm.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Sasha Levin

locking/qspinlock: Remove unbounded cmpxchg() loop from locking slowpath

2018-12-21T13:11:33+00:00

commit 59fb586b4a07b4e1a0ee577140ab4842ba451acd upstream.

The qspinlock locking slowpath utilises a "pending" bit as a simple form
of an embedded test-and-set lock that can avoid the overhead of explicit
queuing in cases where the lock is held but uncontended. This bit is
managed using a cmpxchg() loop which tries to transition the uncontended
lock word from (0,0,0) -> (0,0,1) or (0,0,1) -> (0,1,1).

Unfortunately, the cmpxchg() loop is unbounded and lockers can be starved
indefinitely if the lock word is seen to oscillate between unlocked
(0,0,0) and locked (0,0,1). This could happen if concurrent lockers are
able to take the lock in the cmpxchg() loop without queuing and pass it
around amongst themselves.

This patch fixes the problem by unconditionally setting _Q_PENDING_VAL
using atomic_fetch_or, and then inspecting the old value to see whether
we need to spin on the current lock owner, or whether we now effectively
hold the lock. The tricky scenario is when concurrent lockers end up
queuing on the lock and the lock becomes available, causing us to see
a lockword of (n,0,0). With pending now set, simply queuing could lead
to deadlock as the head of the queue may not have observed the pending
flag being cleared. Conversely, if the head of the queue did observe
pending being cleared, then it could transition the lock from (n,0,0) ->
(0,0,1) meaning that any attempt to "undo" our setting of the pending
bit could race with a concurrent locker trying to set it.

We handle this race by preserving the pending bit when taking the lock
after reaching the head of the queue and leaving the tail entry intact
if we saw pending set, because we know that the tail is going to be
updated shortly.

Signed-off-by: Will Deacon 
Acked-by: Peter Zijlstra (Intel) 
Acked-by: Waiman Long 
Cc: Linus Torvalds 
Cc: Thomas Gleixner 
Cc: boqun.feng@gmail.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1524738868-31318-6-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Sasha Levin