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[tip:core/objtool] bpf: Mark __bpf_prog_run() stack frame as non-standard

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Commit-ID:  39853cc0cdcf1b11f00f7f81e2f515a4d68ed209
Gitweb:     http://git.kernel.org/tip/39853cc0cdcf1b11f00f7f81e2f515a4d68ed209
Author:     Josh Poimboeuf <jpoimboe@redhat.com>
AuthorDate: Sun, 28 Feb 2016 22:22:37 -0600
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 29 Feb 2016 08:35:11 +0100

bpf: Mark __bpf_prog_run() stack frame as non-standard

objtool reports the following false positive warnings:

  kernel/bpf/core.o: warning: objtool: __bpf_prog_run()+0x5c: sibling call from callable instruction with changed frame pointer
  kernel/bpf/core.o: warning: objtool: __bpf_prog_run()+0x60: function has unreachable instruction
  kernel/bpf/core.o: warning: objtool: __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: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Bernd Petrovitsch <bernd@petrovitsch.priv.at>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris J Arges <chris.j.arges@canonical.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Pedro Alves <palves@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Cc: netdev@vger.kernel.org
Link: http://lkml.kernel.org/r/b90e6bf3fdbfb5c4cc1b164b965502e53cf48935.1456719558.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@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)

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[PATCH v19 00/10] Compile-time stack metadata validation Josh Poimboeuf <jpoimboe@redhat.com> - 2016-02-29 05:30 +0100
  [PATCH v19 06/10] sched: always inline context_switch() Josh Poimboeuf <jpoimboe@redhat.com> - 2016-02-29 05:30 +0100
    [tip:core/objtool] sched: Always inline context_switch() tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-02-29 12:10 +0100
  [PATCH v19 09/10] objtool: Add CONFIG_STACK_VALIDATION option Josh Poimboeuf <jpoimboe@redhat.com> - 2016-02-29 05:30 +0100
    [tip:core/objtool] objtool: Add CONFIG_STACK_VALIDATION option tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-02-29 12:10 +0100
      Re: [tip:core/objtool] objtool: Add CONFIG_STACK_VALIDATION option Sebastian Andrzej Siewior <sebastian@breakpoint.cc> - 2016-03-03 15:20 +0100
        Re: [tip:core/objtool] objtool: Add CONFIG_STACK_VALIDATION option Josh Poimboeuf <jpoimboe@redhat.com> - 2016-03-03 16:00 +0100
  [PATCH v19 01/10] objtool: Mark non-standard files and directories Josh Poimboeuf <jpoimboe@redhat.com> - 2016-02-29 05:30 +0100
    [tip:core/objtool] objtool: Mark non-standard object files and  directories tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-02-29 12:00 +0100
  [PATCH v19 07/10] x86/kprobes: Mark kretprobe_trampoline() stack frame as non-standard Josh Poimboeuf <jpoimboe@redhat.com> - 2016-02-29 05:30 +0100
    [tip:core/objtool] x86/kprobes: Mark kretprobe_trampoline() stack  frame as non-standard tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-02-29 12:10 +0100
  [PATCH v19 10/10] objtool: Enable stack metadata validation on x86_64 Josh Poimboeuf <jpoimboe@redhat.com> - 2016-02-29 05:30 +0100
    [tip:core/objtool] objtool: Enable stack metadata validation on  64-bit x86 tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-02-29 12:10 +0100
  [PATCH v19 04/10] bpf: Mark __bpf_prog_run() stack frame as non-standard Josh Poimboeuf <jpoimboe@redhat.com> - 2016-02-29 05:30 +0100
    [tip:core/objtool] bpf: Mark __bpf_prog_run() stack frame as  non-standard tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-02-29 12:10 +0100
  [PATCH v19 03/10] x86/xen: Mark xen_cpuid() stack frame as non-standard Josh Poimboeuf <jpoimboe@redhat.com> - 2016-02-29 05:30 +0100
    [tip:core/objtool] x86/xen: Mark xen_cpuid() stack frame as  non-standard tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-02-29 12:10 +0100

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