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Groups > linux.kernel > #1343551 > unrolled thread

[PATCH v18 0/9] Compile-time stack metadata validation

Started byJosh Poimboeuf <jpoimboe@redhat.com>
First post2016-02-26 00:00 +0100
Last post2016-02-28 08:00 +0100
Articles 10 — 2 participants

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Contents

  [PATCH v18 0/9] Compile-time stack metadata validation Josh Poimboeuf <jpoimboe@redhat.com> - 2016-02-26 00:00 +0100
    [PATCH v18 3/9] x86/xen: Mark xen_cpuid() stack frame as non-standard Josh Poimboeuf <jpoimboe@redhat.com> - 2016-02-26 00:00 +0100
    [PATCH v18 2/9] objtool: Add STACK_FRAME_NON_STANDARD macro Josh Poimboeuf <jpoimboe@redhat.com> - 2016-02-26 00:00 +0100
    [PATCH v18 4/9] bpf: Mark __bpf_prog_run() stack frame as non-standard Josh Poimboeuf <jpoimboe@redhat.com> - 2016-02-26 00:00 +0100
    [PATCH v18 1/9] objtool: Mark non-standard files and directories Josh Poimboeuf <jpoimboe@redhat.com> - 2016-02-26 00:00 +0100
    [PATCH v18 5/9] sched: Mark __schedule() stack frame as non-standard Josh Poimboeuf <jpoimboe@redhat.com> - 2016-02-26 00:00 +0100
    [PATCH v18 8/9] objtool: Add CONFIG_STACK_VALIDATION option Josh Poimboeuf <jpoimboe@redhat.com> - 2016-02-26 00:00 +0100
    Re: [PATCH v18 0/9] Compile-time stack metadata validation Ingo Molnar <mingo@kernel.org> - 2016-02-28 08:00 +0100
      Re: [PATCH v18 0/9] Compile-time stack metadata validation Josh Poimboeuf <jpoimboe@redhat.com> - 2016-02-28 18:10 +0100
    Re: [PATCH v18 0/9] Compile-time stack metadata validation Ingo Molnar <mingo@kernel.org> - 2016-02-28 08:00 +0100

#1343551 — [PATCH v18 0/9] Compile-time stack metadata validation

FromJosh Poimboeuf <jpoimboe@redhat.com>
Date2016-02-26 00:00 +0100
Subject[PATCH v18 0/9] Compile-time stack metadata validation
Message-ID<r6d33-2h5-5@gated-at.bofh.it>
This is v18 of the compile-time stack metadata validation patch set.

It's based on tip:core/objtool.

v17 can be found here:

  https://lkml.kernel.org/r/cover.1456331595.git.jpoimboe@redhat.com

For more information about the motivation behind this patch set, and
more details about what it does, see the patch 7 changelog and
tools/objtool/Documentation/stack-validation.txt.

Patches 1-6 mark various directories, files, and functions as
"non-standard".

Patches 7-9 add objtool and integrate it into the kernel build.

v18:
- include/linux/objtool.h -> include/linux/frame.h
- __objtool_ignore_func -> __func_stack_frame_non_standard
- reword commit messages and comments a bit
- reorder patches

v17:
- __ex_table fix
- rename stacktool -> objtool
- STACKTOOL_IGNORE_FUNCTION -> STACK_FRAME_NON_STANDARD
- 'STACKTOOL := n' -> 'OBJECT_FILES_NON_STANDARD := y'
- updated global_noreturns list

v16:
- fix all allyesconfig warnings, except for staging
- get rid of STACKTOOL_IGNORE_INSN which is no longer needed
- remove several whitelists in favor of automatically whitelisting any
  function with a special instruction like ljmp, lret, or vmrun
- split up stacktool patch into 3 parts as suggested by Ingo
- update the global noreturn function list
- detect noreturn function fallthroughs
- skip weak functions in noreturn call detection logic
- add empty function check to noreturn logic
- allow non-section rela symbols for __ex_table sections
- support rare switch table case with jmpq *[addr](%rip)
- don't warn on frame pointer restore without save
- rearrange patch order a bit

v15:
- restructure code for a new cmdline interface "stacktool check" using
  the new subcommand framework in tools/lib/subcmd
- fix 32 bit build fail (put __sp at end) in paravirt_types.h patch 10
  which was reported by 0day

v14:
- make tools/include/linux/list.h self-sufficient
- create FRAME_OFFSET to allow 32-bit code to be able to access function
  arguments on the stack
- add FRAME_OFFSET usage in crypto patch 14/24: "Create stack frames in
  aesni-intel_asm.S"
- rename "index" -> "idx" to fix build with some compilers

v13:
- LDFLAGS order fix from Chris J Arges
- new warning fix patches from Chris J Arges
- "--frame-pointer" -> "--check-frame-pointer"

v12:
- rename "stackvalidate" -> "stacktool"
- move from scripts/ to tools/:
  - makefile rework
  - make a copy of the x86 insn code (and warn if the code diverges)
  - use tools/include/linux/list.h
- move warning macros to a new warn.h file
- change wording: "stack validation" -> "stack metadata validation"

v11:
- attempt to answer the "why" question better in the documentation and
  commit message
- s/FP_SAVE/FRAME_BEGIN/ in documentation

v10:
- add scripts/mod to directory ignores
- remove circular dependencies for ignored objects which are built
  before stackvalidate
- fix CONFIG_MODVERSIONS incompatibility

v9:
- rename FRAME/ENDFRAME -> FRAME_BEGIN/FRAME_END
- fix jump table issue for when the original instruction is a jump
- drop paravirt thunk alignment patch
- add maintainers to CC for proposed warning fixes

v8:
- add proposed fixes for warnings
- fix all memory leaks
- process ignores earlier and add more ignore checks
- always assume POPCNT alternative is enabled
- drop hweight inline asm fix
- drop __schedule() ignore patch
- change .Ltemp_\@ to .Lstackvalidate_ignore_\@ in asm macro
- fix CONFIG_* checks in asm macros
- add C versions of ignore macros and frame macros
- change ";" to "\n" in C macros
- add ifdef CONFIG_STACK_VALIDATION checks in C ignore macros
- use numbered label in C ignore macro
- add missing break in switch case statement in arch-x86.c

v7:
- sibling call support
- document proposed solution for inline asm() frame pointer issues
- say "kernel entry/exit" instead of "context switch"
- clarify the checking of switch statement jump tables
- discard __stackvalidate_ignore_* sections in linker script
- use .Ltemp_\@ to get a unique label instead of static 3-digit number
- change STACKVALIDATE_IGNORE_FUNC variable to a static
- move STACKVALIDATE_IGNORE_INSN to arch-specific .h file

v6:
- rename asmvalidate -> stackvalidate (again)
- gcc-generated object file support
- recursive branch state analysis
- external jump support
- fixup/exception table support
- jump label support
- switch statement jump table support
- added documentation
- detection of "noreturn" dead end functions
- added a Kbuild mechanism for skipping files and dirs
- moved frame pointer macros to arch/x86/include/asm/frame.h
- moved ignore macros to include/linux/stackvalidate.h

v5:
- stackvalidate -> asmvalidate
- frame pointers only required for non-leaf functions
- check for the use of the FP_SAVE/RESTORE macros instead of manually
  analyzing code to detect frame pointer usage
- additional checks to ensure each function doesn't leave its boundaries
- make the macros simpler and more flexible
- support for analyzing ALTERNATIVE macros
- simplified the arch interfaces in scripts/asmvalidate/arch.h
- fixed some asmvalidate warnings
- rebased onto latest tip asm cleanups
- many more small changes

v4:
- Changed the default to CONFIG_STACK_VALIDATION=n, until all the asm
  code can get cleaned up.
- Fixed a stackvalidate error path exit code issue found by Michal
  Marek.

v3:
- Added a patch to make the push/pop CFI macros arch-independent, as
  suggested by H. Peter Anvin

v2:
- Fixed memory leaks reported by Petr Mladek

Cc: linux-kernel@vger.kernel.org
Cc: live-patching@vger.kernel.org
Cc: Michal Marek <mmarek@suse.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Pedro Alves <palves@redhat.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Bernd Petrovitsch <bernd@petrovitsch.priv.at>
Cc: Chris J Arges <chris.j.arges@canonical.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>

Josh Poimboeuf (9):
  objtool: Mark non-standard files and directories
  objtool: Add STACK_FRAME_NON_STANDARD macro
  x86/xen: Mark xen_cpuid() stack frame as non-standard
  bpf: Mark __bpf_prog_run() stack frame as non-standard
  sched: Mark __schedule() stack frame as non-standard
  x86/kprobes: Mark kretprobe_trampoline() stack frame as non-standard
  objtool: Compile-time stack metadata validation
  objtool: Add CONFIG_STACK_VALIDATION option
  objtool: Enable stack metadata validation on x86_64

 MAINTAINERS                                       |   5 +
 Makefile                                          |   5 +-
 arch/Kconfig                                      |   6 +
 arch/x86/Kconfig                                  |   1 +
 arch/x86/boot/Makefile                            |   3 +-
 arch/x86/boot/compressed/Makefile                 |   3 +-
 arch/x86/entry/Makefile                           |   4 +
 arch/x86/entry/vdso/Makefile                      |   6 +-
 arch/x86/kernel/Makefile                          |  11 +-
 arch/x86/kernel/kprobes/core.c                    |   2 +
 arch/x86/kernel/vmlinux.lds.S                     |   5 +-
 arch/x86/platform/efi/Makefile                    |   2 +
 arch/x86/purgatory/Makefile                       |   2 +
 arch/x86/realmode/Makefile                        |   4 +-
 arch/x86/realmode/rm/Makefile                     |   3 +-
 arch/x86/xen/enlighten.c                          |   3 +-
 drivers/firmware/efi/libstub/Makefile             |   1 +
 include/linux/frame.h                             |  23 +
 kernel/bpf/core.c                                 |   2 +
 kernel/sched/core.c                               |   2 +
 lib/Kconfig.debug                                 |  12 +
 scripts/Makefile.build                            |  39 +-
 scripts/mod/Makefile                              |   2 +
 tools/Makefile                                    |  14 +-
 tools/objtool/.gitignore                          |   2 +
 tools/objtool/Build                               |  13 +
 tools/objtool/Documentation/stack-validation.txt  | 340 ++++++++
 tools/objtool/Makefile                            |  60 ++
 tools/objtool/arch.h                              |  44 +
 tools/objtool/arch/x86/Build                      |  12 +
 tools/objtool/arch/x86/decode.c                   | 172 ++++
 tools/objtool/arch/x86/insn/gen-insn-attr-x86.awk | 387 +++++++++
 tools/objtool/arch/x86/insn/inat.c                |  97 +++
 tools/objtool/arch/x86/insn/inat.h                | 221 +++++
 tools/objtool/arch/x86/insn/inat_types.h          |  29 +
 tools/objtool/arch/x86/insn/insn.c                | 594 +++++++++++++
 tools/objtool/arch/x86/insn/insn.h                | 201 +++++
 tools/objtool/arch/x86/insn/x86-opcode-map.txt    | 984 +++++++++++++++++++++
 tools/objtool/builtin-check.c                     | 993 ++++++++++++++++++++++
 tools/objtool/builtin.h                           |  22 +
 tools/objtool/elf.c                               | 403 +++++++++
 tools/objtool/elf.h                               |  79 ++
 tools/objtool/objtool.c                           | 134 +++
 tools/objtool/special.c                           | 193 +++++
 tools/objtool/special.h                           |  42 +
 tools/objtool/warn.h                              |  60 ++
 46 files changed, 5220 insertions(+), 22 deletions(-)
 create mode 100644 include/linux/frame.h
 create mode 100644 tools/objtool/.gitignore
 create mode 100644 tools/objtool/Build
 create mode 100644 tools/objtool/Documentation/stack-validation.txt
 create mode 100644 tools/objtool/Makefile
 create mode 100644 tools/objtool/arch.h
 create mode 100644 tools/objtool/arch/x86/Build
 create mode 100644 tools/objtool/arch/x86/decode.c
 create mode 100644 tools/objtool/arch/x86/insn/gen-insn-attr-x86.awk
 create mode 100644 tools/objtool/arch/x86/insn/inat.c
 create mode 100644 tools/objtool/arch/x86/insn/inat.h
 create mode 100644 tools/objtool/arch/x86/insn/inat_types.h
 create mode 100644 tools/objtool/arch/x86/insn/insn.c
 create mode 100644 tools/objtool/arch/x86/insn/insn.h
 create mode 100644 tools/objtool/arch/x86/insn/x86-opcode-map.txt
 create mode 100644 tools/objtool/builtin-check.c
 create mode 100644 tools/objtool/builtin.h
 create mode 100644 tools/objtool/elf.c
 create mode 100644 tools/objtool/elf.h
 create mode 100644 tools/objtool/objtool.c
 create mode 100644 tools/objtool/special.c
 create mode 100644 tools/objtool/special.h
 create mode 100644 tools/objtool/warn.h

-- 
2.4.3

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#1343553 — [PATCH v18 3/9] x86/xen: Mark xen_cpuid() stack frame as non-standard

FromJosh Poimboeuf <jpoimboe@redhat.com>
Date2016-02-26 00:00 +0100
Subject[PATCH v18 3/9] x86/xen: Mark xen_cpuid() stack frame as non-standard
Message-ID<r6d34-2h5-15@gated-at.bofh.it>
In reply to#1343551
'objtool check' reports the following false positive warning:

  objtool: arch/x86/xen/enlighten.o: xen_cpuid()+0x41: can't find jump dest instruction at .text+0x108

The warning is due to xen_cpuid()'s use of XEN_EMULATE_PREFIX to insert
some fake instructions which objtool doesn't know how to decode.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
 arch/x86/xen/enlighten.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index d09e4c9..5c45a69 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -32,6 +32,7 @@
 #include <linux/gfp.h>
 #include <linux/memblock.h>
 #include <linux/edd.h>
+#include <linux/frame.h>
 
 #ifdef CONFIG_KEXEC_CORE
 #include <linux/kexec.h>
@@ -351,8 +352,8 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
 	*cx &= maskecx;
 	*cx |= setecx;
 	*dx &= maskedx;
-
 }
+STACK_FRAME_NON_STANDARD(xen_cpuid); /* XEN_EMULATE_PREFIX */
 
 static bool __init xen_check_mwait(void)
 {
-- 
2.4.3

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#1343554 — [PATCH v18 2/9] objtool: Add STACK_FRAME_NON_STANDARD macro

FromJosh Poimboeuf <jpoimboe@redhat.com>
Date2016-02-26 00:00 +0100
Subject[PATCH v18 2/9] objtool: Add STACK_FRAME_NON_STANDARD macro
Message-ID<r6d34-2h5-19@gated-at.bofh.it>
In reply to#1343551
Add a new macro, STACK_FRAME_NON_STANDARD, which is used to denote a
function which does something unusual related to its stack frame.  Use
of the macro prevents objtool from emitting a false positive warning.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 arch/x86/kernel/vmlinux.lds.S |  5 ++++-
 include/linux/frame.h         | 23 +++++++++++++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)
 create mode 100644 include/linux/frame.h

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 92dc211..13fa0ad 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -343,7 +343,10 @@ SECTIONS
 
 	/* Sections to be discarded */
 	DISCARDS
-	/DISCARD/ : { *(.eh_frame) }
+	/DISCARD/ : {
+		*(.eh_frame)
+		*(__func_stack_frame_non_standard)
+	}
 }
 
 
diff --git a/include/linux/frame.h b/include/linux/frame.h
new file mode 100644
index 0000000..e6baaba
--- /dev/null
+++ b/include/linux/frame.h
@@ -0,0 +1,23 @@
+#ifndef _LINUX_FRAME_H
+#define _LINUX_FRAME_H
+
+#ifdef CONFIG_STACK_VALIDATION
+/*
+ * This macro marks the given function's stack frame as "non-standard", which
+ * tells objtool to ignore the function when doing stack metadata validation.
+ * It should only be used in special cases where you're 100% sure it won't
+ * affect the reliability of frame pointers and kernel stack traces.
+ *
+ * For more information, see tools/objtool/Documentation/stack-validation.txt.
+ */
+#define STACK_FRAME_NON_STANDARD(func) \
+	static void __used __section(__func_stack_frame_non_standard) \
+		*__func_stack_frame_non_standard_##func = func
+
+#else /* !CONFIG_STACK_VALIDATION */
+
+#define STACK_FRAME_NON_STANDARD(func)
+
+#endif /* CONFIG_STACK_VALIDATION */
+
+#endif /* _LINUX_FRAME_H */
-- 
2.4.3

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#1343556 — [PATCH v18 4/9] bpf: Mark __bpf_prog_run() stack frame as non-standard

FromJosh Poimboeuf <jpoimboe@redhat.com>
Date2016-02-26 00:00 +0100
Subject[PATCH v18 4/9] bpf: Mark __bpf_prog_run() stack frame as non-standard
Message-ID<r6d34-2h5-25@gated-at.bofh.it>
In reply to#1343551
objtool reports the following false positive warnings:

  objtool: kernel/bpf/core.o: __bpf_prog_run()+0x5c: sibling call from callable instruction with changed frame pointer
  objtool: kernel/bpf/core.o: __bpf_prog_run()+0x60: function has unreachable instruction
  objtool: kernel/bpf/core.o: __bpf_prog_run()+0x64: function has unreachable instruction
  [...]

It's confused by the following dynamic jump instruction in
__bpf_prog_run()::

  jmp     *(%r12,%rax,8)

which corresponds to the following line in the C code:

  goto *jumptable[insn->code];

There's no way for objtool to deterministically find all possible
branch targets for a dynamic jump, so it can't verify this code.

In this case the jumps all stay within the function, and there's nothing
unusual going on related to the stack, so we can whitelist the function.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Cc: netdev@vger.kernel.org
---
 kernel/bpf/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 972d9a8..be0abf6 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -27,6 +27,7 @@
 #include <linux/random.h>
 #include <linux/moduleloader.h>
 #include <linux/bpf.h>
+#include <linux/frame.h>
 
 #include <asm/unaligned.h>
 
@@ -649,6 +650,7 @@ load_byte:
 		WARN_RATELIMIT(1, "unknown opcode %02x\n", insn->code);
 		return 0;
 }
+STACK_FRAME_NON_STANDARD(__bpf_prog_run); /* jump table */
 
 bool bpf_prog_array_compatible(struct bpf_array *array,
 			       const struct bpf_prog *fp)
-- 
2.4.3

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#1343557 — [PATCH v18 1/9] objtool: Mark non-standard files and directories

FromJosh Poimboeuf <jpoimboe@redhat.com>
Date2016-02-26 00:00 +0100
Subject[PATCH v18 1/9] objtool: Mark non-standard files and directories
Message-ID<r6d34-2h5-23@gated-at.bofh.it>
In reply to#1343551
Code which runs outside the kernel's normal mode of operation often does
unusual things which can cause a static analysis tool like objtool to
emit false positive warnings:

- boot image
- vdso image
- relocation
- realmode
- efi
- head
- purgatory
- modpost

Set OBJECT_FILES_NON_STANDARD for their related files and directories,
which will tell objtool to skip checking them.  It's ok to skip them
because they don't affect runtime stack traces.

Also skip the following code which does the right thing with respect to
frame pointers, but is too "special" to be validated by a tool:

- entry
- mcount

Also skip the test_nx module because it modifies its exception handling
table at runtime, which objtool can't understand.  Fortunately it's
just a test module so it doesn't matter much.

Currently objtool is the only user of OBJECT_FILES_NON_STANDARD, but it
might eventually be useful for other tools.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 arch/x86/boot/Makefile                |  3 ++-
 arch/x86/boot/compressed/Makefile     |  3 ++-
 arch/x86/entry/Makefile               |  4 ++++
 arch/x86/entry/vdso/Makefile          |  6 ++++--
 arch/x86/kernel/Makefile              | 11 ++++++++---
 arch/x86/platform/efi/Makefile        |  2 ++
 arch/x86/purgatory/Makefile           |  2 ++
 arch/x86/realmode/Makefile            |  4 +++-
 arch/x86/realmode/rm/Makefile         |  3 ++-
 drivers/firmware/efi/libstub/Makefile |  1 +
 scripts/mod/Makefile                  |  2 ++
 11 files changed, 32 insertions(+), 9 deletions(-)

diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
index bbe1a62..0bf6749 100644
--- a/arch/x86/boot/Makefile
+++ b/arch/x86/boot/Makefile
@@ -9,7 +9,8 @@
 # Changed by many, many contributors over the years.
 #
 
-KASAN_SANITIZE := n
+KASAN_SANITIZE			:= n
+OBJECT_FILES_NON_STANDARD	:= y
 
 # If you want to preset the SVGA mode, uncomment the next line and
 # set SVGA_MODE to whatever number you want.
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index f9ce75d..5e1d26e 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -16,7 +16,8 @@
 #	(see scripts/Makefile.lib size_append)
 #	compressed vmlinux.bin.all + u32 size of vmlinux.bin.all
 
-KASAN_SANITIZE := n
+KASAN_SANITIZE			:= n
+OBJECT_FILES_NON_STANDARD	:= y
 
 targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \
 	vmlinux.bin.xz vmlinux.bin.lzo vmlinux.bin.lz4
diff --git a/arch/x86/entry/Makefile b/arch/x86/entry/Makefile
index bd55ded..fe91c25 100644
--- a/arch/x86/entry/Makefile
+++ b/arch/x86/entry/Makefile
@@ -1,6 +1,10 @@
 #
 # Makefile for the x86 low level entry code
 #
+
+OBJECT_FILES_NON_STANDARD_entry_$(BITS).o   := y
+OBJECT_FILES_NON_STANDARD_entry_64_compat.o := y
+
 obj-y				:= entry_$(BITS).o thunk_$(BITS).o syscall_$(BITS).o
 obj-y				+= common.o
 
diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
index c854541..f9fb859 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -3,8 +3,9 @@
 #
 
 KBUILD_CFLAGS += $(DISABLE_LTO)
-KASAN_SANITIZE := n
-UBSAN_SANITIZE := n
+KASAN_SANITIZE			:= n
+UBSAN_SANITIZE			:= n
+OBJECT_FILES_NON_STANDARD	:= y
 
 VDSO64-$(CONFIG_X86_64)		:= y
 VDSOX32-$(CONFIG_X86_X32_ABI)	:= y
@@ -16,6 +17,7 @@ vobjs-y := vdso-note.o vclock_gettime.o vgetcpu.o
 
 # files to link into kernel
 obj-y				+= vma.o
+OBJECT_FILES_NON_STANDARD_vma.o	:= n
 
 # vDSO images to build
 vdso_img-$(VDSO64-y)		+= 64
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index b1b78ff..d5fb087 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -16,9 +16,14 @@ CFLAGS_REMOVE_ftrace.o = -pg
 CFLAGS_REMOVE_early_printk.o = -pg
 endif
 
-KASAN_SANITIZE_head$(BITS).o := n
-KASAN_SANITIZE_dumpstack.o := n
-KASAN_SANITIZE_dumpstack_$(BITS).o := n
+KASAN_SANITIZE_head$(BITS).o				:= n
+KASAN_SANITIZE_dumpstack.o				:= n
+KASAN_SANITIZE_dumpstack_$(BITS).o			:= n
+
+OBJECT_FILES_NON_STANDARD_head_$(BITS).o		:= y
+OBJECT_FILES_NON_STANDARD_relocate_kernel_$(BITS).o	:= y
+OBJECT_FILES_NON_STANDARD_mcount_$(BITS).o		:= y
+OBJECT_FILES_NON_STANDARD_test_nx.o			:= y
 
 CFLAGS_irq.o := -I$(src)/../include/asm/trace
 
diff --git a/arch/x86/platform/efi/Makefile b/arch/x86/platform/efi/Makefile
index 2846aaa..066619b 100644
--- a/arch/x86/platform/efi/Makefile
+++ b/arch/x86/platform/efi/Makefile
@@ -1,3 +1,5 @@
+OBJECT_FILES_NON_STANDARD_efi_thunk_$(BITS).o := y
+
 obj-$(CONFIG_EFI) 		+= quirks.o efi.o efi_$(BITS).o efi_stub_$(BITS).o
 obj-$(CONFIG_ACPI_BGRT) += efi-bgrt.o
 obj-$(CONFIG_EARLY_PRINTK_EFI)	+= early_printk.o
diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
index 2c835e3..92e3e1d 100644
--- a/arch/x86/purgatory/Makefile
+++ b/arch/x86/purgatory/Makefile
@@ -1,3 +1,5 @@
+OBJECT_FILES_NON_STANDARD := y
+
 purgatory-y := purgatory.o stack.o setup-x86_$(BITS).o sha256.o entry64.o string.o
 
 targets += $(purgatory-y)
diff --git a/arch/x86/realmode/Makefile b/arch/x86/realmode/Makefile
index e02c2c6..682c895 100644
--- a/arch/x86/realmode/Makefile
+++ b/arch/x86/realmode/Makefile
@@ -6,7 +6,9 @@
 # for more details.
 #
 #
-KASAN_SANITIZE := n
+KASAN_SANITIZE			:= n
+OBJECT_FILES_NON_STANDARD	:= y
+
 subdir- := rm
 
 obj-y += init.o
diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile
index 3e75fcf..053abe7b0 100644
--- a/arch/x86/realmode/rm/Makefile
+++ b/arch/x86/realmode/rm/Makefile
@@ -6,7 +6,8 @@
 # for more details.
 #
 #
-KASAN_SANITIZE := n
+KASAN_SANITIZE			:= n
+OBJECT_FILES_NON_STANDARD	:= y
 
 always := realmode.bin realmode.relocs
 
diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
index aaf9c0b..68fa977 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -23,6 +23,7 @@ KBUILD_CFLAGS			:= $(cflags-y) -DDISABLE_BRANCH_PROFILING \
 GCOV_PROFILE			:= n
 KASAN_SANITIZE			:= n
 UBSAN_SANITIZE			:= n
+OBJECT_FILES_NON_STANDARD	:= y
 
 lib-y				:= efi-stub-helper.o
 
diff --git a/scripts/mod/Makefile b/scripts/mod/Makefile
index c11212f..19d9bca 100644
--- a/scripts/mod/Makefile
+++ b/scripts/mod/Makefile
@@ -1,3 +1,5 @@
+OBJECT_FILES_NON_STANDARD := y
+
 hostprogs-y	:= modpost mk_elfconfig
 always		:= $(hostprogs-y) empty.o
 
-- 
2.4.3

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#1343559 — [PATCH v18 5/9] sched: Mark __schedule() stack frame as non-standard

FromJosh Poimboeuf <jpoimboe@redhat.com>
Date2016-02-26 00:00 +0100
Subject[PATCH v18 5/9] sched: Mark __schedule() stack frame as non-standard
Message-ID<r6d34-2h5-27@gated-at.bofh.it>
In reply to#1343551
objtool reports the following warnings for __schedule():

  objtool: kernel/sched/core.o: __schedule()+0x3c0: duplicate frame pointer save
  objtool: kernel/sched/core.o: __schedule()+0x3fd: sibling call from callable instruction with changed frame pointer
  objtool: kernel/sched/core.o: __schedule()+0x40a: call without frame pointer save/setup
  objtool: kernel/sched/core.o: __schedule()+0x7fd: frame pointer state mismatch
  objtool: kernel/sched/core.o: __schedule()+0x421: frame pointer state mismatch

Basically it's confused by two unusual attributes of the switch_to()
macro:

1. It saves prev's frame pointer to the old stack and restores next's
   frame pointer from the new stack.

2. For new tasks it jumps directly to ret_from_fork.

Eventually it would probably be a good idea to clean up the
ret_from_fork hack so that new tasks are created with a valid initial
stack, as suggested by Andy:

  https://lkml.kernel.org/r/CALCETrWsqCw4L1qKO9j9L5F+4ED4viuLQTFc=n1pKBZfFPQUFg@mail.gmail.com

Then __schedule() could return normally into the new code and objtool
hopefully wouldn't have a problem anymore.

In the meantime, mark its stack frame as non-standard so we can have a
baseline with no objtool warnings.  The marker also serves as a reminder
that this code could be improved a bit.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 kernel/sched/core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9503d59..641043d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -74,6 +74,7 @@
 #include <linux/binfmts.h>
 #include <linux/context_tracking.h>
 #include <linux/compiler.h>
+#include <linux/frame.h>
 
 #include <asm/switch_to.h>
 #include <asm/tlb.h>
@@ -3288,6 +3289,7 @@ static void __sched notrace __schedule(bool preempt)
 
 	balance_callback(rq);
 }
+STACK_FRAME_NON_STANDARD(__schedule); /* switch_to() */
 
 static inline void sched_submit_work(struct task_struct *tsk)
 {
-- 
2.4.3

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#1343560 — [PATCH v18 8/9] objtool: Add CONFIG_STACK_VALIDATION option

FromJosh Poimboeuf <jpoimboe@redhat.com>
Date2016-02-26 00:00 +0100
Subject[PATCH v18 8/9] objtool: Add CONFIG_STACK_VALIDATION option
Message-ID<r6d34-2h5-31@gated-at.bofh.it>
In reply to#1343551
Add a CONFIG_STACK_VALIDATION option which will run "objtool check" for
each .o file to ensure the validity of its stack metadata.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 Makefile               |  5 ++++-
 arch/Kconfig           |  6 ++++++
 lib/Kconfig.debug      | 12 ++++++++++++
 scripts/Makefile.build | 39 +++++++++++++++++++++++++++++++++++----
 4 files changed, 57 insertions(+), 5 deletions(-)

diff --git a/Makefile b/Makefile
index fbe1b92..62be03b 100644
--- a/Makefile
+++ b/Makefile
@@ -993,7 +993,10 @@ prepare0: archprepare FORCE
 	$(Q)$(MAKE) $(build)=.
 
 # All the preparing..
-prepare: prepare0
+prepare: prepare0 prepare-objtool
+
+PHONY += prepare-objtool
+prepare-objtool: $(if $(CONFIG_STACK_VALIDATION), tools/objtool FORCE)
 
 # Generate some files
 # ---------------------------------------------------------------------------
diff --git a/arch/Kconfig b/arch/Kconfig
index f6b649d..81869a5 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -583,6 +583,12 @@ config HAVE_COPY_THREAD_TLS
 	  normal C parameter passing, rather than extracting the syscall
 	  argument from pt_regs.
 
+config HAVE_STACK_VALIDATION
+	bool
+	help
+	  Architecture supports the 'objtool check' host tool command, which
+	  performs compile-time stack metadata validation.
+
 #
 # ABI hall of shame
 #
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 8bfd1ac..8552656 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -342,6 +342,18 @@ config FRAME_POINTER
 	  larger and slower, but it gives very useful debugging information
 	  in case of kernel bugs. (precise oopses/stacktraces/warnings)
 
+config STACK_VALIDATION
+	bool "Compile-time stack metadata validation"
+	depends on HAVE_STACK_VALIDATION
+	default n
+	help
+	  Add compile-time checks to validate stack metadata, including frame
+	  pointers (if CONFIG_FRAME_POINTER is enabled).  This helps ensure
+	  that runtime stack traces are more reliable.
+
+	  For more information, see
+	  tools/objtool/Documentation/stack-validation.txt.
+
 config DEBUG_FORCE_WEAK_PER_CPU
 	bool "Force weak per-cpu definitions"
 	depends on DEBUG_KERNEL
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 2c47f9c..130a452 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -241,10 +241,32 @@ cmd_record_mcount =						\
 	fi;
 endif
 
+ifdef CONFIG_STACK_VALIDATION
+
+__objtool_obj := $(objtree)/tools/objtool/objtool
+
+objtool_args = check
+ifndef CONFIG_FRAME_POINTER
+objtool_args += --no-fp
+endif
+
+# 'OBJECT_FILES_NON_STANDARD := y': skip objtool checking for a directory
+# 'OBJECT_FILES_NON_STANDARD_foo.o := 'y': skip objtool checking for a file
+# 'OBJECT_FILES_NON_STANDARD_foo.o := 'n': override directory skip for a file
+cmd_objtool = $(if $(patsubst y%,, \
+	$(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n), \
+	$(__objtool_obj) $(objtool_args) "$(@)";)
+objtool_obj = $(if $(patsubst y%,, \
+	$(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n), \
+	$(__objtool_obj))
+
+endif # CONFIG_STACK_VALIDATION
+
 define rule_cc_o_c
 	$(call echo-cmd,checksrc) $(cmd_checksrc)			  \
 	$(call echo-cmd,cc_o_c) $(cmd_cc_o_c);				  \
 	$(cmd_modversions)						  \
+	$(cmd_objtool)						  \
 	$(call echo-cmd,record_mcount)					  \
 	$(cmd_record_mcount)						  \
 	scripts/basic/fixdep $(depfile) $@ '$(call make-cmd,cc_o_c)' >    \
@@ -253,14 +275,23 @@ define rule_cc_o_c
 	mv -f $(dot-target).tmp $(dot-target).cmd
 endef
 
+define rule_as_o_S
+	$(call echo-cmd,as_o_S) $(cmd_as_o_S);				  \
+	$(cmd_objtool)						  \
+	scripts/basic/fixdep $(depfile) $@ '$(call make-cmd,as_o_S)' >    \
+	                                              $(dot-target).tmp;  \
+	rm -f $(depfile);						  \
+	mv -f $(dot-target).tmp $(dot-target).cmd
+endef
+
 # Built-in and composite module parts
-$(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE
+$(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_obj) FORCE
 	$(call cmd,force_checksrc)
 	$(call if_changed_rule,cc_o_c)
 
 # Single-part modules are special since we need to mark them in $(MODVERDIR)
 
-$(single-used-m): $(obj)/%.o: $(src)/%.c $(recordmcount_source) FORCE
+$(single-used-m): $(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_obj) FORCE
 	$(call cmd,force_checksrc)
 	$(call if_changed_rule,cc_o_c)
 	@{ echo $(@:.o=.ko); echo $@; } > $(MODVERDIR)/$(@F:.o=.mod)
@@ -290,8 +321,8 @@ $(obj)/%.s: $(src)/%.S FORCE
 quiet_cmd_as_o_S = AS $(quiet_modtag)  $@
 cmd_as_o_S       = $(CC) $(a_flags) -c -o $@ $<
 
-$(obj)/%.o: $(src)/%.S FORCE
-	$(call if_changed_dep,as_o_S)
+$(obj)/%.o: $(src)/%.S $(objtool_obj) FORCE
+	$(call if_changed_rule,as_o_S)
 
 targets += $(real-objs-y) $(real-objs-m) $(lib-y)
 targets += $(extra-y) $(MAKECMDGOALS) $(always)
-- 
2.4.3

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#1345175

FromIngo Molnar <mingo@kernel.org>
Date2016-02-28 08:00 +0100
Message-ID<r73uG-6XB-1@gated-at.bofh.it>
In reply to#1343551
Another thing I've noticed are _thousands_ of these warnings:

objtool: kernel/sched/core.o: preempt_schedule_irq()+0x20: function has unreachable instruction
objtool: kernel/sched/core.o: preempt_schedule_irq()+0x27: function has unreachable instruction
objtool: kernel/sched/core.o: preempt_schedule_irq()+0x2c: function has unreachable instruction
objtool: kernel/sched/core.o: preempt_schedule_irq()+0x33: function has unreachable instruction
objtool: net/ceph/pagevec.o: ceph_put_page_vector()+0x171: function has unreachable instruction
objtool: net/ceph/pagevec.o: ceph_put_page_vector()+0x178: function has unreachable instruction
objtool: net/ceph/pagevec.o: ceph_put_page_vector()+0x17d: function has unreachable instruction
objtool: net/ceph/pagevec.o: ceph_put_page_vector()+0x184: function has unreachable instruction
objtool: net/ceph/pagevec.o: ceph_get_direct_page_vector()+0xe2: function has unreachable instruction
objtool: net/ceph/pagevec.o: ceph_get_direct_page_vector()+0xe9: function has unreachable instruction
objtool: net/ceph/pagevec.o: ceph_get_direct_page_vector()+0xee: function has unreachable instruction
objtool: net/ceph/pagevec.o: ceph_get_direct_page_vector()+0xf5: function has unreachable instruction
objtool: net/ceph/pagevec.o: zero_user_segment()+0x120: function has unreachable instruction
objtool: net/ceph/pagevec.o: zero_user_segment()+0x127: function has unreachable instruction
objtool: net/ceph/pagevec.o: zero_user_segment()+0x12c: function has unreachable instruction
objtool: net/ceph/pagevec.o: zero_user_segment()+0x133: function has unreachable instruction

that's on an x86-64 allyesconfig kernel, with objtool merged to tip:master, using 
GCC 4.9.2:

  gcc version 4.9.2 20150212 (Red Hat 4.9.2-6) (GCC) 

Also, please prefix such warnings with the standard compiler prefix, something 
like this:

	kernel/sched/core.c: warning: objtool: preempt_schedule_irq()+0x20: function has unreachable instruction

so that scripts/tools monitoring new build warnings can pick them up 
automatically?

Thanks,

	Ingo

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#1345360

FromJosh Poimboeuf <jpoimboe@redhat.com>
Date2016-02-28 18:10 +0100
Message-ID<r7d0Z-5MI-1@gated-at.bofh.it>
In reply to#1345175
On Sun, Feb 28, 2016 at 07:57:29AM +0100, Ingo Molnar wrote:
> 
> Another thing I've noticed are _thousands_ of these warnings:
> 
> objtool: kernel/sched/core.o: preempt_schedule_irq()+0x20: function has unreachable instruction
> objtool: kernel/sched/core.o: preempt_schedule_irq()+0x27: function has unreachable instruction
> objtool: kernel/sched/core.o: preempt_schedule_irq()+0x2c: function has unreachable instruction
> objtool: kernel/sched/core.o: preempt_schedule_irq()+0x33: function has unreachable instruction
> objtool: net/ceph/pagevec.o: ceph_put_page_vector()+0x171: function has unreachable instruction
> objtool: net/ceph/pagevec.o: ceph_put_page_vector()+0x178: function has unreachable instruction
> objtool: net/ceph/pagevec.o: ceph_put_page_vector()+0x17d: function has unreachable instruction
> objtool: net/ceph/pagevec.o: ceph_put_page_vector()+0x184: function has unreachable instruction
> objtool: net/ceph/pagevec.o: ceph_get_direct_page_vector()+0xe2: function has unreachable instruction
> objtool: net/ceph/pagevec.o: ceph_get_direct_page_vector()+0xe9: function has unreachable instruction
> objtool: net/ceph/pagevec.o: ceph_get_direct_page_vector()+0xee: function has unreachable instruction
> objtool: net/ceph/pagevec.o: ceph_get_direct_page_vector()+0xf5: function has unreachable instruction
> objtool: net/ceph/pagevec.o: zero_user_segment()+0x120: function has unreachable instruction
> objtool: net/ceph/pagevec.o: zero_user_segment()+0x127: function has unreachable instruction
> objtool: net/ceph/pagevec.o: zero_user_segment()+0x12c: function has unreachable instruction
> objtool: net/ceph/pagevec.o: zero_user_segment()+0x133: function has unreachable instruction
> 
> that's on an x86-64 allyesconfig kernel, with objtool merged to tip:master, using 
> GCC 4.9.2:
> 
>   gcc version 4.9.2 20150212 (Red Hat 4.9.2-6) (GCC) 

Those are caused by CONFIG_KASAN, CONFIG_UBSAN, and CONFIG_GCOV_KERNEL,
which can all add unreachable instructions.  Technically, an unreachable
instruction isn't really a problem, but objtool warns about it because
it often means there's something going on in the control flow which it
doesn't understand.

I guess we could make CONFIG_STACK_VALIDATION conflict with those
options, but I think that would disable it on allyesconfig.

I'll see if I can make objtool smarter so that it detects these special
cases of unreachable instructions and ignores them.

> Also, please prefix such warnings with the standard compiler prefix, something 
> like this:
> 
> 	kernel/sched/core.c: warning: objtool: preempt_schedule_irq()+0x20: function has unreachable instruction
> 
> so that scripts/tools monitoring new build warnings can pick them up 
> automatically?

Yeah, good idea.

--
Josh

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#1345176

FromIngo Molnar <mingo@kernel.org>
Date2016-02-28 08:00 +0100
Message-ID<r73uG-6XB-3@gated-at.bofh.it>
In reply to#1343551
FYI, I got this build failure on allmodconfig-x86-64:

  objtool.c:134:1: error: control reaches end of non-void function [-Werror=return-type]

that was with:

  gcc version 4.8.3 20140911 (Red Hat 4.8.3-7) (GCC) 

GCC 5.2.1 does not trigger this warning, which is I suspect why you have not seen 
this in your own testing.

I applied the fix below: all paths that generate a nonzero error do an explicit 
exit(), so return 0 is fine here.

Thanks,

	Ingo

=====================>

 tools/objtool/objtool.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/objtool/objtool.c b/tools/objtool/objtool.c
index 4e53d272c0c3..46c326db4f46 100644
--- a/tools/objtool/objtool.c
+++ b/tools/objtool/objtool.c
@@ -131,4 +131,6 @@ int main(int argc, const char **argv)
 		cmd_usage();
 
 	handle_internal_command(argc, argv);
+
+	return 0;
 }

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