linux-toradex.git/arch/s390/include/asm/uaccess.h, branch v4.4.97

s390/uaccess: get_user() should zero on failure (again)

2017-04-12T10:38:34+00:00

commit d09c5373e8e4eaaa09233552cbf75dc4c4f21203 upstream.

Commit fd2d2b191fe7 ("s390: get_user() should zero on failure")
intended to fix s390's get_user() implementation which did not zero
the target operand if the read from user space faulted. Unfortunately
the patch has no effect: the corresponding inline assembly specifies
that the operand is only written to ("=") and the previous value is
discarded.

Therefore the compiler is free to and actually does omit the zero
initialization.

To fix this simply change the contraint modifier to "+", so the
compiler cannot omit the initialization anymore.

Fixes: c9ca78415ac1 ("s390/uaccess: provide inline variants of get_user/put_user")
Fixes: fd2d2b191fe7 ("s390: get_user() should zero on failure")
Cc: Al Viro 
Signed-off-by: Heiko Carstens 
Signed-off-by: Martin Schwidefsky 
Signed-off-by: Greg Kroah-Hartman

s390: get_user() should zero on failure

2016-09-24T08:07:44+00:00

commit fd2d2b191fe75825c4c7a6f12f3fef35aaed7dd7 upstream.

Signed-off-by: Al Viro 
Signed-off-by: Greg Kroah-Hartman

mm/uaccess, mm/fault: Clarify that uaccess may only sleep if pagefaults are enabled

2015-05-19T06:39:14+00:00

In general, non-atomic variants of user access functions must not sleep
if pagefaults are disabled.

Let's update all relevant comments in uaccess code. This also reflects
the might_sleep() checks in might_fault().

Reviewed-and-tested-by: Thomas Gleixner 
Signed-off-by: David Hildenbrand 
Signed-off-by: Peter Zijlstra (Intel) 
Cc: David.Laight@ACULAB.COM
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: airlied@linux.ie
Cc: akpm@linux-foundation.org
Cc: benh@kernel.crashing.org
Cc: bigeasy@linutronix.de
Cc: borntraeger@de.ibm.com
Cc: daniel.vetter@intel.com
Cc: heiko.carstens@de.ibm.com
Cc: herbert@gondor.apana.org.au
Cc: hocko@suse.cz
Cc: hughd@google.com
Cc: mst@redhat.com
Cc: paulus@samba.org
Cc: ralf@linux-mips.org
Cc: schwidefsky@de.ibm.com
Cc: yang.shi@windriver.com
Link: http://lkml.kernel.org/r/1431359540-32227-4-git-send-email-dahi@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar

s390/maccess: remove potentially broken probe_kernel_write()

2015-03-25T10:49:43+00:00

Remove the s390 architecture implementation of probe_kernel_write() and
instead use a new function s390_kernel_write() to modify kernel text and
data everywhere.

The s390 implementation of probe_kernel_write() was potentially broken
since it modified memory in a read-modify-write fashion, which read four
bytes, modified the requested bytes within those four bytes and wrote
the result back.
If two cpus would modify the same four byte area at different locations
within that area, this could lead to corruption.
Right now the only places which called probe_kernel_write() did run within
stop_machine_run. Therefore the scenario can't happen right now, however
that might change at any time.

To fix this rename probe_kernel_write() to s390_kernel_write() which can
have special semantics, like only call it while running within stop_machine().

Signed-off-by: Heiko Carstens 
Signed-off-by: Martin Schwidefsky

s390/uaccess: provide inline variants of get_user/put_user

2014-05-20T06:58:50+00:00

This shortens the code by ~17k (performace_defconfig, march=z196).
The number of exception table entries however increases from 164
entries to 2500 entries (+~18k).
However the executed code is shorter and also faster since we save
the branches to the out-of-line copy_to/from_user implementations.

Signed-off-by: Heiko Carstens 
Signed-off-by: Martin Schwidefsky

s390/uaccess: rework uaccess code - fix locking issues

2014-04-03T12:31:04+00:00

The current uaccess code uses a page table walk in some circumstances,
e.g. in case of the in atomic futex operations or if running on old
hardware which doesn't support the mvcos instruction.

However it turned out that the page table walk code does not correctly
lock page tables when accessing page table entries.
In other words: a different cpu may invalidate a page table entry while
the current cpu inspects the pte. This may lead to random data corruption.

Adding correct locking however isn't trivial for all uaccess operations.
Especially copy_in_user() is problematic since that requires to hold at
least two locks, but must be protected against ABBA deadlock when a
different cpu also performs a copy_in_user() operation.

So the solution is a different approach where we change address spaces:

User space runs in primary address mode, or access register mode within
vdso code, like it currently already does.

The kernel usually also runs in home space mode, however when accessing
user space the kernel switches to primary or secondary address mode if
the mvcos instruction is not available or if a compare-and-swap (futex)
instruction on a user space address is performed.
KVM however is special, since that requires the kernel to run in home
address space while implicitly accessing user space with the sie
instruction.

So we end up with:

User space:
- runs in primary or access register mode
- cr1 contains the user asce
- cr7 contains the user asce
- cr13 contains the kernel asce

Kernel space:
- runs in home space mode
- cr1 contains the user or kernel asce
  -> the kernel asce is loaded when a uaccess requires primary or
     secondary address mode
- cr7 contains the user or kernel asce, (changed with set_fs())
- cr13 contains the kernel asce

In case of uaccess the kernel changes to:
- primary space mode in case of a uaccess (copy_to_user) and uses
  e.g. the mvcp instruction to access user space. However the kernel
  will stay in home space mode if the mvcos instruction is available
- secondary space mode in case of futex atomic operations, so that the
  instructions come from primary address space and data from secondary
  space

In case of kvm the kernel runs in home space mode, but cr1 gets switched
to contain the gmap asce before the sie instruction gets executed. When
the sie instruction is finished cr1 will be switched back to contain the
user asce.

A context switch between two processes will always load the kernel asce
for the next process in cr1. So the first exit to user space is a bit
more expensive (one extra load control register instruction) than before,
however keeps the code rather simple.

In sum this means there is no need to perform any error prone page table
walks anymore when accessing user space.

The patch seems to be rather large, however it mainly removes the
the page table walk code and restores the previously deleted "standard"
uaccess code, with a couple of changes.

The uaccess without mvcos mode can be enforced with the "uaccess_primary"
kernel parameter.

Reported-by: Christian Borntraeger 
Signed-off-by: Heiko Carstens 
Signed-off-by: Martin Schwidefsky

s390/uaccess: remove copy_from_user_real()

2014-02-24T16:14:00+00:00

There is no user left, so remove it.
It was also potentially broken, since the function didn't clear destination
memory if copy_from_user() failed. Which would allow for information leaks.

Signed-off-by: Heiko Carstens 
Signed-off-by: Martin Schwidefsky

s390/uaccess: consistent types

2014-02-21T07:50:15+00:00

The types 'size_t' and 'unsigned long' have been used randomly for the
uaccess functions. This looks rather confusing.
So let's change all functions to use unsigned long instead and get rid
of size_t in order to have a consistent interface.

The only exception is strncpy_from_user() which uses 'long' since it
may return a signed value (-EFAULT).

Signed-off-by: Heiko Carstens 
Signed-off-by: Martin Schwidefsky

s390/uaccess: get rid of indirect function calls

2014-02-21T07:50:14+00:00

There are only two uaccess variants on s390 left: the version that is used
if the mvcos instruction is available, and the page table walk variant.
So there is no need for expensive indirect function calls.

By default the mvcos variant will be called. If the mvcos instruction is not
available it will call the page table walk variant.

For minimal performance impact the "if (mvcos_is_available)" is implemented
with a jump label, which will be a six byte nop on machines with mvcos.

Signed-off-by: Heiko Carstens 
Signed-off-by: Martin Schwidefsky

s390/uaccess: normalize order of parameters of indirect uaccess function calls

2014-02-21T07:50:13+00:00

For some unknown reason the indirect uaccess functions on s390 implement a
different parameter order than what is usual.

e.g.:

unsigned long copy_to_user(void *to, const void *from, unsigned long n);
vs.
size_t (*copy_to_user)(size_t n, void __user * to, const void *from);

Let's get rid of this confusing parameter reordering.

Signed-off-by: Heiko Carstens 
Signed-off-by: Martin Schwidefsky