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Linus Torvalds 33692f2759 vm: add VM_FAULT_SIGSEGV handling support 
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 fee7e49d45 ("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 <tiwai@suse.de>
Tested-by: Jan Engelhardt <jengelh@inai.de>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com> # "s390 still compiles and boots"
Cc: linux-arch@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 		2015-01-29 10:51:32 -08:00
..
configs arch/um: make it work with defconfig and x86_64 2013-11-17 11:31:48 +01:00
drivers uml: Fix unsafe pid reference to foreground process group 2014-11-05 16:26:13 -08:00
include Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2014-12-11 14:27:06 -08:00
kernel vm: add VM_FAULT_SIGSEGV handling support 2015-01-29 10:51:32 -08:00
os-Linux Revert "um: Fix wait_stub_done() error handling" 2014-07-20 12:56:34 +02:00
scripts um: Preinclude include/linux/kern_levels.h 2012-09-27 20:20:09 +02:00
sys-ia64 uml: remove useless comments 2009-04-01 08:59:17 -07:00
sys-ppc dump_stack: unify debug information printed by show_regs() 2013-04-30 17:04:02 -07:00
.gitignore um: tell git to ignore generated files 2010-03-06 11:26:28 -08:00
Kconfig.char um: remove used STDIO_CONSOLE Kconfig param 2013-11-17 11:32:27 +01:00
Kconfig.common um: Skip futex_atomic_cmpxchg_inatomic() test 2015-01-04 14:20:26 +01:00
Kconfig.debug lib: consolidate DEBUG_STACK_USAGE option 2011-05-25 08:39:54 -07:00
Kconfig.net arch/um: remove depends on CONFIG_EXPERIMENTAL 2013-01-11 11:38:04 -08:00
Kconfig.rest um: switch to use of drivers/Kconfig 2011-11-02 14:15:41 +01:00
Kconfig.um arch/um: remove depends on CONFIG_EXPERIMENTAL 2013-01-11 11:38:04 -08:00
Makefile um: Fix for relative objtree when generating x86 headers 2014-06-05 17:55:48 +02:00
Makefile-ia64
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Makefile-os-Linux x86, um: get rid of arch/um/os symlink 2008-10-22 22:55:22 -07:00
Makefile-ppc
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Makefile-skas
…