linux-stable.git/arch/x86/kernel/process_32.c, branch linux-4.9.y

sched/x86: Save [ER]FLAGS on context switch

2019-05-21T16:48:56+00:00

commit 6690e86be83ac75832e461c141055b5d601c0a6d upstream.

Effectively reverts commit:

  2c7577a75837 ("sched/x86_64: Don't save flags on context switch")

Specifically because SMAP uses FLAGS.AC which invalidates the claim
that the kernel has clean flags.

In particular; while preemption from interrupt return is fine (the
IRET frame on the exception stack contains FLAGS) it breaks any code
that does synchonous scheduling, including preempt_enable().

This has become a significant issue ever since commit:

  5b24a7a2aa20 ("Add 'unsafe' user access functions for batched accesses")

provided for means of having 'normal' C code between STAC / CLAC,
exposing the FLAGS.AC state. So far this hasn't led to trouble,
however fix it before it comes apart.

Reported-by: Julien Thierry 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Josh Poimboeuf 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: stable@kernel.org
Fixes: 5b24a7a2aa20 ("Add 'unsafe' user access functions for batched accesses")
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

x86/process: Consolidate and simplify switch_to_xtra() code

2019-05-14T17:19:38+00:00

commit ff16701a29cba3aafa0bd1656d766813b2d0a811 upstream.

Move the conditional invocation of __switch_to_xtra() into an inline
function so the logic can be shared between 32 and 64 bit.

Remove the handthrough of the TSS pointer and retrieve the pointer directly
in the bitmap handling function. Use this_cpu_ptr() instead of the
per_cpu() indirection.

This is a preparatory change so integration of conditional indirect branch
speculation optimization happens only in one place.

Signed-off-by: Thomas Gleixner 
Reviewed-by: Ingo Molnar 
Cc: Peter Zijlstra 
Cc: Andy Lutomirski 
Cc: Linus Torvalds 
Cc: Jiri Kosina 
Cc: Tom Lendacky 
Cc: Josh Poimboeuf 
Cc: Andrea Arcangeli 
Cc: David Woodhouse 
Cc: Tim Chen 
Cc: Andi Kleen 
Cc: Dave Hansen 
Cc: Casey Schaufler 
Cc: Asit Mallick 
Cc: Arjan van de Ven 
Cc: Jon Masters 
Cc: Waiman Long 
Cc: Greg KH 
Cc: Dave Stewart 
Cc: Kees Cook 
Link: https://lkml.kernel.org/r/20181125185005.280855518@linutronix.de
[bwh: Backported to 4.9:
 - Use cpu_tss instead of cpu_tss_rw
 - __switch_to() still uses the tss variable, so don't delete it
 - Adjust context]
Signed-off-by: Ben Hutchings 
Signed-off-by: Greg Kroah-Hartman

x86/asm: Get rid of __read_cr4_safe()

2016-09-30T10:40:12+00:00

We use __read_cr4() vs __read_cr4_safe() inconsistently.  On
CR4-less CPUs, all CR4 bits are effectively clear, so we can make
the code simpler and more robust by making __read_cr4() always fix
up faults on 32-bit kernels.

This may fix some bugs on old 486-like CPUs, but I don't have any
easy way to test that.

Signed-off-by: Andy Lutomirski 
Cc: Brian Gerst 
Cc: Borislav Petkov 
Cc: david@saggiorato.net
Link: http://lkml.kernel.org/r/ea647033d357d9ce2ad2bbde5a631045f5052fb6.1475178370.git.luto@kernel.org
Signed-off-by: Thomas Gleixner

sched/x86: Fix thread_saved_pc()

2016-08-24T10:31:51+00:00

thread_saved_pc() was using a completely bogus method to get the return
address.  Since switch_to() was previously inlined, there was no sane way
to know where on the stack the return address was stored.  Now with the
frame of a sleeping thread well defined, this can be implemented correctly.

Signed-off-by: Brian Gerst 
Reviewed-by: Josh Poimboeuf 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/1471106302-10159-7-git-send-email-brgerst@gmail.com
Signed-off-by: Ingo Molnar

sched/x86: Pass kernel thread parameters in 'struct fork_frame'

2016-08-24T10:31:50+00:00

Instead of setting up a fake pt_regs context, put the kernel thread
function pointer and arg into the unused callee-restored registers
of 'struct fork_frame'.

Signed-off-by: Brian Gerst 
Reviewed-by: Josh Poimboeuf 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/1471106302-10159-6-git-send-email-brgerst@gmail.com
Signed-off-by: Ingo Molnar

sched/x86: Rewrite the switch_to() code

2016-08-24T10:31:41+00:00

Move the low-level context switch code to an out-of-line asm stub instead of
using complex inline asm.  This allows constructing a new stack frame for the
child process to make it seamlessly flow to ret_from_fork without an extra
test and branch in __switch_to().  It also improves code generation for
__schedule() by using the C calling convention instead of clobbering all
registers.

Signed-off-by: Brian Gerst 
Reviewed-by: Josh Poimboeuf 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/1471106302-10159-5-git-send-email-brgerst@gmail.com
Signed-off-by: Ingo Molnar

x86/kernel: Audit and remove any unnecessary uses of module.h

2016-07-14T13:06:41+00:00

Historically a lot of these existed because we did not have
a distinction between what was modular code and what was providing
support to modules via EXPORT_SYMBOL and friends.  That changed
when we forked out support for the latter into the export.h file.

This means we should be able to reduce the usage of module.h
in code that is obj-y Makefile or bool Kconfig.  The advantage
in doing so is that module.h itself sources about 15 other headers;
adding significantly to what we feed cpp, and it can obscure what
headers we are effectively using.

Since module.h was the source for init.h (for __init) and for
export.h (for EXPORT_SYMBOL) we consider each obj-y/bool instance
for the presence of either and replace as needed.  Build testing
revealed some implicit header usage that was fixed up accordingly.

Note that some bool/obj-y instances remain since module.h is
the header for some exception table entry stuff, and for things
like __init_or_module (code that is tossed when MODULES=n).

Signed-off-by: Paul Gortmaker 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/20160714001901.31603-4-paul.gortmaker@windriver.com
Signed-off-by: Ingo Molnar

sched/core, sched/x86: Kill thread_info::saved_preempt_count

2015-10-06T15:08:18+00:00

With the introduction of the context switch preempt_count invariant,
and the demise of PREEMPT_ACTIVE, its pointless to save/restore the
per-cpu preemption count, it must always be 2.

Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Thomas Gleixner 
Reviewed-by: Frederic Weisbecker 
Cc: Linus Torvalds 
Cc: Mike Galbraith 
Cc: Peter Zijlstra 
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar

x86/process: Unify 32bit and 64bit implementations of get_wchan()

2015-09-30T19:51:34+00:00

The stack layout and the functionality is identical. Use the 64bit
version for all of x86.

Signed-off-by: Thomas Gleixner 
Reviewed-by: Borislav Petkov 
Reviewed-by: Dmitry Vyukov 
Cc: Andrey Ryabinin 
Cc: Andy Lutomirski 
Cc: Andrey Konovalov 
Cc: Kostya Serebryany 
Cc: Alexander Potapenko 
Cc: kasan-dev 
Cc: Denys Vlasenko 
Cc: Andi Kleen 
Cc: Sasha Levin 
Cc: Wolfram Gloger 
Link: http://lkml.kernel.org/r/20150930083302.779694618@linutronix.de
Signed-off-by: Thomas Gleixner

x86/vm86: Clean up vm86.h includes

2015-07-31T11:31:10+00:00

vm86.h was being implicitly included in alot of places via
processor.h, which in turn got it from math_emu.h.  Break that
chain and explicitly include vm86.h in all files that need it.
Also remove unused vm86 field from math_emu_info.

Signed-off-by: Brian Gerst 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/1438148483-11932-7-git-send-email-brgerst@gmail.com
[ Fixed build failure. ]
Signed-off-by: Ingo Molnar