linux-toradex.git/arch/x86/include/asm, branch v4.4.35

Fix potential infoleak in older kernels

2016-11-10T15:36:34+00:00

Not upstream as it is not needed there.

So a patch something like this might be a safe way to fix the
potential infoleak in older kernels.

THIS IS UNTESTED. It's a very obvious patch, though, so if it compiles
it probably works. It just initializes the output variable with 0 in
the inline asm description, instead of doing it in the exception
handler.

It will generate slightly worse code (a few unnecessary ALU
operations), but it doesn't have any interactions with the exception
handler implementation.


Signed-off-by: Greg Kroah-Hartman

Revert "fix minor infoleak in get_user_ex()"

2016-11-01T01:56:26+00:00

This reverts commit 9d25c78ec01c402dc56272693c44ef9d72ecdd2e which is
1c109fabbd51863475cd12ac206bdd249aee35af upstream

Cc: Al Viro 
Cc: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

Revert "x86/mm: Expand the exception table logic to allow new handling options"

2016-11-01T01:56:26+00:00

This reverts commit fcf5e5198b447969ed2a56ec335dae3c695a6b46 which is
548acf19234dbda5a52d5a8e7e205af46e9da840 upstream.

Cc: Tony Luck 
Cc: Borislav Petkov 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

x86/mm: Expand the exception table logic to allow new handling options

2016-10-31T10:14:00+00:00

commit 548acf19234dbda5a52d5a8e7e205af46e9da840 upstream.

Huge amounts of help from  Andy Lutomirski and Borislav Petkov to
produce this. Andy provided the inspiration to add classes to the
exception table with a clever bit-squeezing trick, Boris pointed
out how much cleaner it would all be if we just had a new field.

Linus Torvalds blessed the expansion with:

  ' I'd rather not be clever in order to save just a tiny amount of space
    in the exception table, which isn't really criticial for anybody. '

The third field is another relative function pointer, this one to a
handler that executes the actions.

We start out with three handlers:

 1: Legacy - just jumps the to fixup IP
 2: Fault - provide the trap number in %ax to the fixup code
 3: Cleaned up legacy for the uaccess error hack

Signed-off-by: Tony Luck 
Reviewed-by: Borislav Petkov 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/f6af78fcbd348cf4939875cfda9c19689b5e50b8.1455732970.git.tony.luck@intel.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

x86/init: Fix cr4_init_shadow() on CR4-less machines

2016-10-07T13:23:40+00:00

commit e1bfc11c5a6f40222a698a818dc269113245820e upstream.

cr4_init_shadow() will panic on 486-like machines without CR4.  Fix
it using __read_cr4_safe().

Reported-by: david@saggiorato.net
Signed-off-by: Andy Lutomirski 
Reviewed-by: Borislav Petkov 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Josh Poimboeuf 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Fixes: 1e02ce4cccdc ("x86: Store a per-cpu shadow copy of CR4")
Link: http://lkml.kernel.org/r/43a20f81fb504013bf613913dc25574b45336a61.1475091074.git.luto@kernel.org
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

fix minor infoleak in get_user_ex()

2016-09-24T08:07:43+00:00

commit 1c109fabbd51863475cd12ac206bdd249aee35af upstream.

get_user_ex(x, ptr) should zero x on failure.  It's not a lot of a leak
(at most we are leaking uninitialized 64bit value off the kernel stack,
and in a fairly constrained situation, at that), but the fix is trivial,
so...

Signed-off-by: Al Viro 
[ This sat in different branch from the uaccess fixes since mid-August ]
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

x86/mm: Disable preemption during CR3 read+write

2016-09-07T06:32:35+00:00

commit 5cf0791da5c162ebc14b01eb01631cfa7ed4fa6e upstream.

There's a subtle preemption race on UP kernels:

Usually current->mm (and therefore mm->pgd) stays the same during the
lifetime of a task so it does not matter if a task gets preempted during
the read and write of the CR3.

But then, there is this scenario on x86-UP:

TaskA is in do_exit() and exit_mm() sets current->mm = NULL followed by:

 -> mmput()
 -> exit_mmap()
 -> tlb_finish_mmu()
 -> tlb_flush_mmu()
 -> tlb_flush_mmu_tlbonly()
 -> tlb_flush()
 -> flush_tlb_mm_range()
 -> __flush_tlb_up()
 -> __flush_tlb()
 ->  __native_flush_tlb()

At this point current->mm is NULL but current->active_mm still points to
the "old" mm.

Let's preempt taskA _after_ native_read_cr3() by taskB. TaskB has its
own mm so CR3 has changed.

Now preempt back to taskA. TaskA has no ->mm set so it borrows taskB's
mm and so CR3 remains unchanged. Once taskA gets active it continues
where it was interrupted and that means it writes its old CR3 value
back. Everything is fine because userland won't need its memory
anymore.

Now the fun part:

Let's preempt taskA one more time and get back to taskB. This
time switch_mm() won't do a thing because oldmm (->active_mm)
is the same as mm (as per context_switch()). So we remain
with a bad CR3 / PGD and return to userland.

The next thing that happens is handle_mm_fault() with an address for
the execution of its code in userland. handle_mm_fault() realizes that
it has a PTE with proper rights so it returns doing nothing. But the
CPU looks at the wrong PGD and insists that something is wrong and
faults again. And again. And one more time…

This pagefault circle continues until the scheduler gets tired of it and
puts another task on the CPU. It gets little difficult if the task is a
RT task with a high priority. The system will either freeze or it gets
fixed by the software watchdog thread which usually runs at RT-max prio.
But waiting for the watchdog will increase the latency of the RT task
which is no good.

Fix this by disabling preemption across the critical code section.

Signed-off-by: Sebastian Andrzej Siewior 
Acked-by: Peter Zijlstra (Intel) 
Acked-by: Rik van Riel 
Acked-by: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Josh Poimboeuf 
Cc: Linus Torvalds 
Cc: Mel Gorman 
Cc: Peter Zijlstra 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/1470404259-26290-1-git-send-email-bigeasy@linutronix.de
[ Prettified the changelog. ]
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

x86/xen, pat: Remove PAT table init code from Xen

2016-08-16T07:30:49+00:00

commit 88ba281108ed0c25c9d292b48bd3f272fcb90dd0 upstream.

Xen supports PAT without MTRRs for its guests.  In order to
enable WC attribute, it was necessary for xen_start_kernel()
to call pat_init_cache_modes() to update PAT table before
starting guest kernel.

Now that the kernel initializes PAT table to the BIOS handoff
state when MTRR is disabled, this Xen-specific PAT init code
is no longer necessary.  Delete it from xen_start_kernel().

Also change __init_cache_modes() to a static function since
PAT table should not be tweaked by other modules.

Signed-off-by: Toshi Kani 
Reviewed-by: Thomas Gleixner 
Acked-by: Juergen Gross 
Cc: Andrew Morton 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Konrad Rzeszutek Wilk 
Cc: Linus Torvalds 
Cc: Luis R. Rodriguez 
Cc: Peter Zijlstra 
Cc: Toshi Kani 
Cc: elliott@hpe.com
Cc: paul.gortmaker@windriver.com
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1458769323-24491-7-git-send-email-toshi.kani@hpe.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

x86/mtrr: Fix Xorg crashes in Qemu sessions

2016-08-16T07:30:49+00:00

commit edfe63ec97ed8d4496225f7ba54c9ce4207c5431 upstream.

A Xorg failure on qemu32 was reported as a regression [1] caused by
commit 9cd25aac1f44 ("x86/mm/pat: Emulate PAT when it is disabled").

This patch fixes the Xorg crash.

Negative effects of this regression were the following two failures [2]
in Xorg on QEMU with QEMU CPU model "qemu32" (-cpu qemu32), which were
triggered by the fact that its virtual CPU does not support MTRRs.

 #1. copy_process() failed in the check in reserve_pfn_range()

    copy_process
     copy_mm
      dup_mm
       dup_mmap
        copy_page_range
         track_pfn_copy
          reserve_pfn_range

 A WC map request was tracked as WC in memtype, which set a PTE as
 UC (pgprot) per __cachemode2pte_tbl[].  This led to this error in
 reserve_pfn_range() called from track_pfn_copy(), which obtained
 a pgprot from a PTE.  It converts pgprot to page_cache_mode, which
 does not necessarily result in the original page_cache_mode since
 __cachemode2pte_tbl[] redirects multiple types to UC.

 #2. error path in copy_process() then hit WARN_ON_ONCE in
     untrack_pfn().

     x86/PAT: Xorg:509 map pfn expected mapping type uncached-
     minus for [mem 0xfd000000-0xfdffffff], got write-combining
      Call Trace:
     dump_stack
     warn_slowpath_common
     ? untrack_pfn
     ? untrack_pfn
     warn_slowpath_null
     untrack_pfn
     ? __kunmap_atomic
     unmap_single_vma
     ? pagevec_move_tail_fn
     unmap_vmas
     exit_mmap
     mmput
     copy_process.part.47
     _do_fork
     SyS_clone
     do_syscall_32_irqs_on
     entry_INT80_32

These negative effects are caused by two separate bugs, but they
can be addressed in separate patches.  Fixing the pat_init() issue
described below addresses the root cause, and avoids Xorg to hit
these cases.

When the CPU does not support MTRRs, MTRR does not call pat_init(),
which leaves PAT enabled without initializing PAT.  This pat_init()
issue is a long-standing issue, but manifested as issue #1 (and then
hit issue #2) with the above-mentioned commit because the memtype
now tracks cache attribute with 'page_cache_mode'.

This pat_init() issue existed before the commit, but we used pgprot
in memtype.  Hence, we did not have issue #1 before.  But WC request
resulted in WT in effect because WC pgrot is actually WT when PAT
is not initialized.  This is not how it was designed to work.  When
PAT is set to disable properly, WC is converted to UC.  The use of
WT can result in a system crash if the target range does not support
WT.  Fortunately, nobody ran into such issue before.

To fix this pat_init() issue, PAT code has been enhanced to provide
pat_disable() interface.  Call this interface when MTRRs are disabled.
By setting PAT to disable properly, PAT bypasses the memtype check,
and avoids issue #1.

  [1]: https://lkml.org/lkml/2016/3/3/828
  [2]: https://lkml.org/lkml/2016/3/4/775

Signed-off-by: Toshi Kani 
Reviewed-by: Thomas Gleixner 
Cc: Andrew Morton 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Juergen Gross 
Cc: Linus Torvalds 
Cc: Luis R. Rodriguez 
Cc: Peter Zijlstra 
Cc: Toshi Kani 
Cc: elliott@hpe.com
Cc: konrad.wilk@oracle.com
Cc: paul.gortmaker@windriver.com
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1458769323-24491-5-git-send-email-toshi.kani@hpe.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

x86/mm/pat: Add pat_disable() interface

2016-08-16T07:30:49+00:00

commit 224bb1e5d67ba0f2872c98002d6a6f991ac6fd4a upstream.

In preparation for fixing a regression caused by:

  9cd25aac1f44 ("x86/mm/pat: Emulate PAT when it is disabled")

... PAT needs to provide an interface that prevents the OS from
initializing the PAT MSR.

PAT MSR initialization must be done on all CPUs using the specific
sequence of operations defined in the Intel SDM.  This requires MTRRs
to be enabled since pat_init() is called as part of MTRR init
from mtrr_rendezvous_handler().

Make pat_disable() as the interface that prevents the OS from
initializing the PAT MSR.  MTRR will call this interface when it
cannot provide the SDM-defined sequence to initialize PAT.

This also assures that pat_disable() called from pat_bsp_init()
will set the PAT table properly when CPU does not support PAT.

Signed-off-by: Toshi Kani 
Reviewed-by: Thomas Gleixner 
Cc: Andrew Morton 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Juergen Gross 
Cc: Linus Torvalds 
Cc: Luis R. Rodriguez 
Cc: Peter Zijlstra 
Cc: Robert Elliott 
Cc: Toshi Kani 
Cc: konrad.wilk@oracle.com
Cc: paul.gortmaker@windriver.com
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1458769323-24491-3-git-send-email-toshi.kani@hpe.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman