linux.git/arch/x86/kernel/entry_64.S, branch master

x86/asm/entry: Move entry_64.S and entry_32.S to arch/x86/entry/

2015-06-03T16:51:28+00:00

Create a new directory hierarchy for the low level x86 entry code:

    arch/x86/entry/*

This will host all the low level glue that is currently scattered
all across arch/x86/.

Start with entry_64.S and entry_32.S.

Cc: Borislav Petkov 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Thomas Gleixner 
Cc: Andy Lutomirski 
Cc: Denys Vlasenko 
Cc: Brian Gerst 
Cc: Peter Zijlstra 
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar

x86/asm/entry/64: Fold identical code paths

2015-06-02T08:10:09+00:00

retint_kernel doesn't require %rcx to be pointing to thread info
(anymore?), and the code on the two alternative paths is - not
really surprisingly - identical.

Signed-off-by: Jan Beulich 
Cc: Andy Lutomirski 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/556C664F020000780007FB64@mail.emea.novell.com
Signed-off-by: Ingo Molnar

x86/debug: Remove perpetually broken, unmaintainable dwarf annotations

2015-06-02T05:57:48+00:00

So the dwarf2 annotations in low level assembly code have
become an increasing hindrance: unreadable, messy macros
mixed into some of the most security sensitive code paths
of the Linux kernel.

These debug info annotations don't even buy the upstream
kernel anything: dwarf driven stack unwinding has caused
problems in the past so it's out of tree, and the upstream
kernel only uses the much more robust framepointers based
stack unwinding method.

In addition to that there's a steady, slow bitrot going
on with these annotations, requiring frequent fixups.
There's no tooling and no functionality upstream that
keeps it correct.

So burn down the sick forest, allowing new, healthier growth:

   27 files changed, 350 insertions(+), 1101 deletions(-)

Someone who has the willingness and time to do this
properly can attempt to reintroduce dwarf debuginfo in x86
assembly code plus dwarf unwinding from first principles,
with the following conditions:

 - it should be maximally readable, and maximally low-key to
   'ordinary' code reading and maintenance.

 - find a build time method to insert dwarf annotations
   automatically in the most common cases, for pop/push
   instructions that manipulate the stack pointer. This could
   be done for example via a preprocessing step that just
   looks for common patterns - plus special annotations for
   the few cases where we want to depart from the default.
   We have hundreds of CFI annotations, so automating most of
   that makes sense.

 - it should come with build tooling checks that ensure that
   CFI annotations are sensible. We've seen such efforts from
   the framepointer side, and there's no reason it couldn't be
   done on the dwarf side.

Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: Frédéric Weisbecker 
Cc: Jan Beulich 
Cc: Josh Poimboeuf 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar

x86/asm/entry/64: Use shorter MOVs from segment registers

2015-05-17T05:57:54+00:00

The "movw %ds,%cx" instruction needs a 0x66 prefix, while
"movl %ds,%ecx" does not.

The difference is that latter form (on 64-bit CPUs)
overwrites the entire %ecx, not only its lower half.

But subsequent code doesn't depend on the value of upper
half of %ecx, so we can safely use the shorter instruction.

The new code is also faster than the old one - now we don't
depend on the old value of %ecx, but this code fragment is
not performance-critical so it does not matter much.

Signed-off-by: Denys Vlasenko 
Cc: Alexei Starovoitov 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Frederic Weisbecker 
Cc: H. Peter Anvin 
Cc: Kees Cook 
Cc: Linus Torvalds 
Cc: Oleg Nesterov 
Cc: Peter Zijlstra 
Cc: Steven Rostedt 
Cc: Thomas Gleixner 
Cc: Will Drewry 
Link: http://lkml.kernel.org/r/1431722346-26585-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar

x86/entry: Define 'cpu_current_top_of_stack' for 64-bit code

2015-05-08T11:50:02+00:00

32-bit code has PER_CPU_VAR(cpu_current_top_of_stack).
64-bit code uses somewhat more obscure: PER_CPU_VAR(cpu_tss + TSS_sp0).

Define the 'cpu_current_top_of_stack' macro on CONFIG_X86_64
as well so that the PER_CPU_VAR(cpu_current_top_of_stack)
expression can be used in both 32-bit and 64-bit code.

Signed-off-by: Denys Vlasenko 
Cc: Alexei Starovoitov 
Cc: Andrew Morton 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Frederic Weisbecker 
Cc: H. Peter Anvin 
Cc: Kees Cook 
Cc: Linus Torvalds 
Cc: Oleg Nesterov 
Cc: Peter Zijlstra 
Cc: Steven Rostedt 
Cc: Thomas Gleixner 
Cc: Will Drewry 
Link: http://lkml.kernel.org/r/1429889495-27850-3-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar

x86/entry: Stop using PER_CPU_VAR(kernel_stack)

2015-05-08T11:43:52+00:00

PER_CPU_VAR(kernel_stack) is redundant:

  - On the 64-bit build, we can use PER_CPU_VAR(cpu_tss + TSS_sp0).
  - On the 32-bit build, we can use PER_CPU_VAR(cpu_current_top_of_stack).

PER_CPU_VAR(kernel_stack) will be deleted by a separate change.

Signed-off-by: Denys Vlasenko 
Cc: Alexei Starovoitov 
Cc: Andrew Morton 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Frederic Weisbecker 
Cc: H. Peter Anvin 
Cc: Kees Cook 
Cc: Linus Torvalds 
Cc: Oleg Nesterov 
Cc: Peter Zijlstra 
Cc: Steven Rostedt 
Cc: Thomas Gleixner 
Cc: Will Drewry 
Link: http://lkml.kernel.org/r/1429889495-27850-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar

Merge branch 'linus' into x86/asm, before applying dependent patch

2015-05-08T11:33:33+00:00

Signed-off-by: Ingo Molnar

x86/asm/entry/64: Clean up usage of TEST insns

2015-05-08T09:07:32+00:00

By the nature of TEST operation, it is often possible
to test a narrower part of the operand:

    "testl $3, mem"  -> "testb $3, mem"

This results in shorter insns, because TEST insn has no
sign-entending byte-immediate forms unlike other ALU ops.

   text	   data	    bss	    dec	    hex	filename
  11674	      0	      0	  11674	   2d9a	entry_64.o.before
  11658	      0	      0	  11658	   2d8a	entry_64.o

Changes in object code:

-	f7 84 24 88 00 00 00 03 00 00 00 	testl  $0x3,0x88(%rsp)
+	f6 84 24 88 00 00 00 03	         	testb  $0x3,0x88(%rsp)
-	f7 44 24 68 03 00 00 00          	testl  $0x3,0x68(%rsp)
+	f6 44 24 68 03                  	testb  $0x3,0x68(%rsp)
-	f7 84 24 90 00 00 00 03 00 00 00	testl  $0x3,0x90(%rsp)
+	f6 84 24 90 00 00 00 03         	testb  $0x3,0x90(%rsp)

Signed-off-by: Denys Vlasenko 
Acked-by: Andy Lutomirski 
Cc: Alexei Starovoitov 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Frederic Weisbecker 
Cc: H. Peter Anvin 
Cc: Kees Cook 
Cc: Linus Torvalds 
Cc: Oleg Nesterov 
Cc: Steven Rostedt 
Cc: Thomas Gleixner 
Cc: Will Drewry 
Link: http://lkml.kernel.org/r/1430140912-7960-2-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar

x86/asm/entry/64: Tidy up JZ insns after TESTs

2015-05-08T09:07:31+00:00

After TESTs, use logically correct JZ/JNZ mnemonics instead of
JE/JNE. This doesn't change code.

Signed-off-by: Denys Vlasenko 
Acked-by: Andy Lutomirski 
Cc: Alexei Starovoitov 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Frederic Weisbecker 
Cc: H. Peter Anvin 
Cc: Kees Cook 
Cc: Linus Torvalds 
Cc: Oleg Nesterov 
Cc: Steven Rostedt 
Cc: Thomas Gleixner 
Cc: Will Drewry 
Link: http://lkml.kernel.org/r/1430140912-7960-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar

x86_64, asm: Work around AMD SYSRET SS descriptor attribute issue

2015-04-27T00:57:38+00:00

AMD CPUs don't reinitialize the SS descriptor on SYSRET, so SYSRET with
SS == 0 results in an invalid usermode state in which SS is apparently
equal to __USER_DS but causes #SS if used.

Work around the issue by setting SS to __KERNEL_DS __switch_to, thus
ensuring that SYSRET never happens with SS set to NULL.

This was exposed by a recent vDSO cleanup.

Fixes: e7d6eefaaa44 x86/vdso32/syscall.S: Do not load __USER32_DS to %ss
Signed-off-by: Andy Lutomirski 
Cc: Peter Anvin 
Cc: Borislav Petkov 
Cc: Denys Vlasenko 
Cc: Brian Gerst 
Signed-off-by: Linus Torvalds