Ensure the address limit is a user-mode segment before returning to
user-mode. Otherwise a process can corrupt kernel-mode memory and
elevate privileges [1].

The set_fs function sets the TIF_SETFS flag to force a slow path on
return. In the slow path, the address limit is checked to be USER_DS if
needed.

The TIF_SETFS flag is added to _TIF_WORK_MASK shifting _TIF_SYSCALL_WORK
for arm instruction immediate support. The global work mask is too big
to used on a single instruction so adapt ret_fast_syscall.

[1] https://bugs.chromium.org/p/project-zero/issues/detail?id=990Signed-off-by: NThomas Garnier <thgarnie@google.com>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: kernel-hardening@lists.openwall.com
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Pratyush Anand <panand@redhat.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Will Drewry <wad@chromium.org>
Cc: linux-api@vger.kernel.org
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Link: http://lkml.kernel.org/r/20170615011203.144108-2-thgarnie@google.com

Remove the #if statement which caused trouble for kernels that support
both ARMv6 and ARMv7.  Older architectures do not implement these bits,
so it should be safe to always clear them.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

When a kernel is built covering ARMv6 to ARMv7, we omit to clear the
IT state when entering a signal handler.  This can cause the first
few instructions to be conditionally executed depending on the parent
context.

In any case, the original test for >= ARMv7 is broken - ARMv6 can have
Thumb-2 support as well, and an ARMv6T2 specific build would omit this
code too.

Relax the test back to ARMv6 or greater.  This results in us always
clearing the IT state bits in the PSR, even on CPUs where these bits
are reserved.  However, they're reserved for the IT state, so this
should cause no harm.

Cc: <stable@vger.kernel.org>
Fixes: d71e1352 ("Clear the IT state when invoking a Thumb-2 signal handler")
Acked-by: NTony Lindgren <tony@atomide.com>
Tested-by: NH. Nikolaus Schaller <hns@goldelico.com>
Tested-by: NGrazvydas Ignotas <notasas@gmail.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Make the "fast" syscall return path fast again.  The addition of IRQ
tracing and context tracking has made this path grossly inefficient.
We can do much better if these options are enabled if we save the
syscall return code on the stack - we then don't need to save a bunch
of registers around every single callout to C code.
Acked-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

As execution domain support is gone we can remove
signal translation from the signal code and remove
exec_domain from thread_info.
Signed-off-by: NRichard Weinberger <richard@nod.at>

If an attacker can cause a controlled kernel stack overflow, overwriting
the restart block is a very juicy exploit target.  This is because the
restart_block is held in the same memory allocation as the kernel stack.

Moving the restart block to struct task_struct prevents this exploit by
making the restart_block harder to locate.

Note that there are other fields in thread_info that are also easy
targets, at least on some architectures.

It's also a decent simplification, since the restart code is more or less
identical on all architectures.

[james.hogan@imgtec.com: metag: align thread_info::supervisor_stack]
Signed-off-by: NAndy Lutomirski <luto@amacapital.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: David Miller <davem@davemloft.net>
Acked-by: NRichard Weinberger <richard@nod.at>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Haavard Skinnemoen <hskinnemoen@gmail.com>
Cc: Hans-Christian Egtvedt <egtvedt@samfundet.no>
Cc: Steven Miao <realmz6@gmail.com>
Cc: Mark Salter <msalter@redhat.com>
Cc: Aurelien Jacquiot <a-jacquiot@ti.com>
Cc: Mikael Starvik <starvik@axis.com>
Cc: Jesper Nilsson <jesper.nilsson@axis.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Richard Kuo <rkuo@codeaurora.org>
Cc: "Luck, Tony" <tony.luck@intel.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Tested-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Chen Liqin <liqin.linux@gmail.com>
Cc: Lennox Wu <lennox.wu@gmail.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
Cc: Chris Zankel <chris@zankel.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: NJames Hogan <james.hogan@imgtec.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This patch remove clear_thread_flag(TIF_UPROBE) in do_work_pending(),
because uprobe_notify_resume() have do this.
Signed-off-by: NYalin Wang <yalin.wang@sonymobile.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Using Rabin Vincent's ARM uprobes patches as a base, enable uprobes
support on ARM.

Caveats:

 - Thumb is not supported
Signed-off-by: NRabin Vincent <rabin@rab.in>
Signed-off-by: NDavid A. Long <dave.long@linaro.org>

The ARM architecture reference specifies that the IT state bits in the
PSR must be all zeros in ARM mode or behavior is unspecified.  On the
Qualcomm Snapdragon S4/Krait architecture CPUs the processor continues
to consider the IT state bits while in ARM mode.  This makes it so
that some instructions are skipped by the CPU.
Signed-off-by: NT.J. Purtell <tj@mobisocial.us>
[rmk+kernel@arm.linux.org.uk: fixed whitespace formatting in patch]
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

In case of BE8 kernel data is in BE order whereas code stays in LE
order. Move sigreturn_codes to separate .S file and use proper
assembler mnemonics for these code snippets. In this case compiler
will take care of proper instructions byteswaps for BE8 case.
Change assumes that sufficiently Thumb-capable tools are used to
build kernel.

Problem was discovered during ltp testing of BE system: all rt_sig*
tests failed. Tested against the same tests in both BE and LE modes.
Signed-off-by: NVictor Kamensky <victor.kamensky@linaro.org>
Reviewed-by: NDave Martin <Dave.Martin@arm.com>
Signed-off-by: NBen Dooks <ben.dooks@codethink.co.uk>

Olof reports that noMMU builds error out with:

arch/arm/kernel/signal.c: In function 'setup_return':
arch/arm/kernel/signal.c:413:25: error: 'mm_context_t' has no member named 'sigpage'

This shows one of the evilnesses of IS_ENABLED().  Get rid of it here
and replace it with #ifdef's - and as no noMMU platform can make use
of sigpage, depend on CONIFG_MMU not CONFIG_ARM_MPU.
Reported-by: NOlof Johansson <olof@lixom.net>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Unfortunately, I never committed the fix to a nasty oops which can
occur as a result of that commit:

------------[ cut here ]------------
kernel BUG at /home/olof/work/batch/include/linux/mm.h:414!
Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM
Modules linked in:
CPU: 0 PID: 490 Comm: killall5 Not tainted 3.11.0-rc3-00288-gabe03080 #53
task: e90acac0 ti: e9be8000 task.ti: e9be8000
PC is at special_mapping_fault+0xa4/0xc4
LR is at __do_fault+0x68/0x48c

This doesn't show up unless you do quite a bit of testing; a simple
boot test does not do this, so all my nightly tests were passing fine.

The reason for this is that install_special_mapping() expects the
page array to stick around, and as this was only inserting one page
which was stored on the kernel stack, that's why this was blowing up.
Reported-by: NOlof Johansson <olof@lixom.net>
Tested-by: NOlof Johansson <olof@lixom.net>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Move the signal handlers into a VDSO page rather than keeping them in
the vectors page.  This allows us to place them randomly within this
page, and also map the page at a random location within userspace
further protecting these code fragments from ROP attacks.  The new
VDSO page is also poisoned in the same way as the vector page.
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Without an MMU it is possible for userspace programs to start executing code
in places that they have no business executing. The MPU allows some level of
protection against this.

This patch protects the vectors page from access by userspace processes.
Userspace tasks that dereference a null pointer are already protected by an
svc at 0x0 that kills them. However when tasks use an offset from a null
pointer (eg a function in a null struct) they miss this carefully placed svc
and enter the exception vectors in user mode, ending up in the kernel.

This patch causes programs that do this to receive a SEGV instead of happily
entering the kernel in user-mode, and hence avoid a 'Bad Mode' panic.

As part of this change it is necessary to make sigreturn happen via the
stack when there is not an sa_restorer function. This change is invisible to
userspace, and irrelevant to code compiled using a uClibc toolchain, which
always uses an sa_restorer function.

Because we don't get to remap the vectors in !MMU kuser_helpers are not
in a defined location, and hence aren't usable. This means we don't need to
worry about keeping them accessible from PL0
Signed-off-by: NJonathan Austin <jonathan.austin@arm.com>
Reviewed-by: NWill Deacon <will.deacon@arm.com>
CC: Nicolas Pitre <nico@linaro.org>
CC: Catalin Marinas <catalin.marinas@arm.com>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

This include is no longer needed.
(seems to be a leftover from try_to_freeze())
Signed-off-by: NRichard Weinberger <richard@nod.at>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

just let do_work_pending() return 1 on normal local restarts and
-1 on those that had been caused by ERESTART_RESTARTBLOCK (and 0
is still "all done, sod off to userland now").  And let the asm
glue flip scno to restart_syscall(2) one if it got negative from
us...

[will: resolved conflicts with audit fixes]
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

This reverts commit 3b0c0622.

We no longer require the restart trampoline for syscall restarting.
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

This reverts commit 433e2f30.

Conflicts:

	arch/arm/kernel/ptrace.c

Reintroduce the new syscall restart handling in preparation for further
patches from Al Viro.
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

This reverts commit 6b5c8045.

Conflicts:

	arch/arm/kernel/ptrace.c

The new syscall restarting code can lead to problems if we take an
interrupt in userspace just before restarting the svc instruction. If
a signal is delivered when returning from the interrupt, the
TIF_SYSCALL_RESTARTSYS will remain set and cause any syscalls executed
from the signal handler to be treated as a restart of the previously
interrupted system call. This includes the final sigreturn call, meaning
that we may fail to exit from the signal context. Furthermore, if a
system call made from the signal handler requires a restart via the
restart_block, it is possible to clear the thread flag and fail to
restart the originally interrupted system call.

The right solution to this problem is to perform the restarting in the
kernel, avoiding the possibility of handling a further signal before the
restart is complete. Since we're almost at -rc6, let's revert the new
method for now and aim for in-kernel restarting at a later date.
Acked-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

This reverts commit fa18484d.

We need the restart trampoline back so that we can revert a related
problematic patch 6b5c8045 ("arm: new
way of handling ERESTART_RESTARTBLOCK").
Acked-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

Does block_sigmask() + tracehook_signal_handler();  called when
sigframe has been successfully built.  All architectures converted
to it; block_sigmask() itself is gone now (merged into this one).

I'm still not too happy with the signature, but that's a separate
story (IMO we need a structure that would contain signal number +
siginfo + k_sigaction, so that get_signal_to_deliver() would fill one,
signal_delivered(), handle_signal() and probably setup...frame() -
take one).
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Only 3 out of 63 do not.  Renamed the current variant to __set_current_blocked(),
added set_current_blocked() that will exclude unblockable signals, switched
open-coded instances to it.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

replace boilerplate "should we use ->saved_sigmask or ->blocked?"
with calls of obvious inlined helper...
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

first fruits of ..._restore_sigmask() helpers: now we can take
boilerplate "signal didn't have a handler, clear RESTORE_SIGMASK
and restore the blocked mask from ->saved_mask" into a common
helper.  Open-coded instances switched...
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

guts of saved_sigmask-based sigsuspend/rt_sigsuspend.  Takes
kernel sigset_t *.

Open-coded instances replaced with calling it.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

new "syscall start" flag; handled in syscall_trace() by switching
syscall number to that of syscall_restart(2).  Restarts of that
kind (ERESTART_RESTARTBLOCK) are handled by setting that bit;
syscall number is not modified until the actual call.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

checking in do_signal() is pointless - if we get there with !user_mode(regs)
(and we might), we'll end up looping indefinitely.  Check in work_pending
and break out of the loop if so.
Acked-by: NRussell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

get_signal_to_deliver() will handle it itself
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Acked-by: NRussell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Add calls to tracehook_report_syscall_{entry,exit} and tracehook_signal_handler
Signed-off-by: NSteven Walter <stevenrwalter@gmail.com>
Signed-off-by: NWade Farnsworth <wade_farnsworth@mentor.com>
Reviewed-by: NWill Deacon <will.deacon@arm.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>