linux-stable.git/arch/um/kernel, branch linux-3.12.y

vm: add VM_FAULT_SIGSEGV handling support

2015-03-12T16:31:25+00:00

commit 33692f27597fcab536d7cbbcc8f52905133e4aa7 upstream.

The core VM already knows about VM_FAULT_SIGBUS, but cannot return a
"you should SIGSEGV" error, because the SIGSEGV case was generally
handled by the caller - usually the architecture fault handler.

That results in lots of duplication - all the architecture fault
handlers end up doing very similar "look up vma, check permissions, do
retries etc" - but it generally works.  However, there are cases where
the VM actually wants to SIGSEGV, and applications _expect_ SIGSEGV.

In particular, when accessing the stack guard page, libsigsegv expects a
SIGSEGV.  And it usually got one, because the stack growth is handled by
that duplicated architecture fault handler.

However, when the generic VM layer started propagating the error return
from the stack expansion in commit fee7e49d4514 ("mm: propagate error
from stack expansion even for guard page"), that now exposed the
existing VM_FAULT_SIGBUS result to user space.  And user space really
expected SIGSEGV, not SIGBUS.

To fix that case, we need to add a VM_FAULT_SIGSEGV, and teach all those
duplicate architecture fault handlers about it.  They all already have
the code to handle SIGSEGV, so it's about just tying that new return
value to the existing code, but it's all a bit annoying.

This is the mindless minimal patch to do this.  A more extensive patch
would be to try to gather up the mostly shared fault handling logic into
one generic helper routine, and long-term we really should do that
cleanup.

Just from this patch, you can generally see that most architectures just
copied (directly or indirectly) the old x86 way of doing things, but in
the meantime that original x86 model has been improved to hold the VM
semaphore for shorter times etc and to handle VM_FAULT_RETRY and other
"newer" things, so it would be a good idea to bring all those
improvements to the generic case and teach other architectures about
them too.

Reported-and-tested-by: Takashi Iwai 
Tested-by: Jan Engelhardt 
Acked-by: Heiko Carstens  # "s390 still compiles and boots"
Cc: linux-arch@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds 
Signed-off-by: Jiri Slaby

uml: check length in exitcode_proc_write()

2013-10-30T19:24:49+00:00

We don't cap the size of buffer from the user so we could write past the
end of the array here.  Only root can write to this file.

Reported-by: Nico Golde 
Reported-by: Fabian Yamaguchi 
Signed-off-by: Dan Carpenter 
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds

arch: mm: pass userspace fault flag to generic fault handler

2013-09-12T22:38:01+00:00

Unlike global OOM handling, memory cgroup code will invoke the OOM killer
in any OOM situation because it has no way of telling faults occuring in
kernel context - which could be handled more gracefully - from
user-triggered faults.

Pass a flag that identifies faults originating in user space from the
architecture-specific fault handlers to generic code so that memcg OOM
handling can be improved.

Signed-off-by: Johannes Weiner 
Reviewed-by: Michal Hocko 
Cc: David Rientjes 
Cc: KAMEZAWA Hiroyuki 
Cc: azurIt 
Cc: KOSAKI Motohiro 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

arch: mm: do not invoke OOM killer on kernel fault OOM

2013-09-12T22:38:01+00:00

Kernel faults are expected to handle OOM conditions gracefully (gup,
uaccess etc.), so they should never invoke the OOM killer.  Reserve this
for faults triggered in user context when it is the only option.

Most architectures already do this, fix up the remaining few.

Signed-off-by: Johannes Weiner 
Reviewed-by: Michal Hocko 
Acked-by: KOSAKI Motohiro 
Cc: David Rientjes 
Cc: KAMEZAWA Hiroyuki 
Cc: azurIt 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

um: Add irq chip um/mask handlers

2013-09-07T08:57:19+00:00

These handlers are not optional and need in our case
dummy implementions to avoid NULL pointer bugs within
the irq core code.

Reported-and-tested-by: Toralf Foester 
Signed-off-by: Richard Weinberger

um: Implement probe_kernel_read()

2013-09-07T08:38:34+00:00

UML needs it's own probe_kernel_read() to handle kernel
mode faults correctly.
The implementation uses mincore() on the host side to detect
whether a page is owned by the UML kernel process.

This fixes also a possible crash when sysrq-t is used.
Starting with 3.10 sysrq-t calls probe_kernel_read() to
read details from the kernel workers. As kernel worker are
completely async pointers may turn NULL while reading them.

Cc: 
Cc: 
Cc:  # 3.10.x
Signed-off-by: Richard Weinberger

um: siginfo cleanup

2013-07-19T09:31:36+00:00

Currently we use both struct siginfo and siginfo_t.
Let's use struct siginfo internally to avoid ongoing
compiler warning. We are allowed to do so because
struct siginfo and siginfo_t are equivalent.

Signed-off-by: Richard Weinberger

um: Mark stub pages mapping with VM_PFNMAP

2013-07-19T08:45:17+00:00

Ensure that a process cannot destroy his stub pages with
using MADV_DONTNEED and friends.

Reported-by: toralf.foerster@gmx.de
Signed-off-by: Richard Weinberger

um: Fix return value of strnlen_user()

2013-07-19T08:45:17+00:00

In case of an error it must not return -EFAULT.
Return 0 like all other archs do.

Reported-by: toralf.foerster@gmx.de
Signed-off-by: Richard Weinberger

mm/um: prepare for removing num_physpages and simplify mem_init()

2013-07-03T23:07:37+00:00

Prepare for removing num_physpages and simplify mem_init().

Signed-off-by: Jiang Liu 
Cc: Jeff Dike 
Cc: Richard Weinberger 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds