linux-kernel - Re: [PATCH v19 00/10] Compile-time stack metadata validation

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Date:	Tue, 8 Mar 2016 16:49:09 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
	Michal Marek <mmarek@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Pedro Alves <palves@...hat.com>,
	Namhyung Kim <namhyung@...il.com>,
	Bernd Petrovitsch <bernd@...rovitsch.priv.at>,
	Chris J Arges <chris.j.arges@...onical.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH v19 00/10] Compile-time stack metadata validation


so there's a much more serious objtool bug that I found today, apparently it can 
get into an infinite loop with certain randconfigs:

   PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND                                                                                                          
104261 mingo     39  19    8672    936    840 R 100.0  0.0 115:03.97 objtool                                                                                                          
104485 mingo     39  19    8672    876    780 R 100.0  0.0 115:03.71 objtool                                                                                                          
115277 mingo     39  19    8808    892    796 R 100.0  0.0 114:59.38 objtool                  

unfortunately 'perf record -g' does not seem to be able to resolve it:

fomalhaut:~> perf record -g -p 104261 -a sleep 1
Warning:
PID/TID switch overriding SYSTEM[ perf record: Woken up 17 times to write data ]
[ perf record: Captured and wrote 4.076 MB perf.data (4015 samples) ]

Samples: 4K of event 'cycles:ppp', Event count (approx.): 3342262267                                                                                                                  
  Children      Self  Command  Shared Object      Symbol                                                                                                                              
+  100.00%     0.00%  objtool  [unknown]          [k] 0x000000000184bf00
+  100.00%     0.00%  objtool  [unknown]          [k] 0x000000000184bf70
+  100.00%     0.00%  objtool  [unknown]          [k] 0x000000000184bfe0
+  100.00%     0.00%  objtool  [unknown]          [k] 0x000000000184c050
+  100.00%     0.00%  objtool  [unknown]          [k] 0x000000000184c0c0
+  100.00%     0.00%  objtool  [unknown]          [k] 0x000000000184c130
+  100.00%     0.00%  objtool  [unknown]          [k] 0x000000000184c1a0
+  100.00%     0.00%  objtool  [unknown]          [k] 0x000000000184c210
+  100.00%     0.00%  objtool  [unknown]          [k] 0x000000000184c280
+  100.00%     0.00%  objtool  [unknown]          [k] 0x000000000184c2f0
+  100.00%     0.00%  objtool  [unknown]          [k] 0x000000000184c360
+  100.00%     0.00%  objtool  [unknown]          [k] 0x000000000184c3d0
+  100.00%     0.00%  objtool  [unknown]          [k] 0x000000000184c440
+  100.00%     0.00%  objtool  [unknown]          [k] 0x000000000184c4b0
+  100.00%     0.00%  objtool  [unknown]          [k] 0x000000000184c520

Plain 'perf top' shows:

Overhead  Shared Object       Symbol                                                                                                                                                  
  95.36%  objtool             [.] validate_branch
   2.36%  objtool             [.] find_symbol_by_offset
   0.50%  libc-2.22.so        [.] __strcmp_sse2_unaligned
   0.47%  [kernel]            [k] nmi
   0.06%  [kernel]            [k] format_decode
   0.05%  objtool             [.] strcmp@plt

I've attached the config that triggers it.

Thanks,

	Ingo

View attachment "config" of type "text/plain" (125609 bytes)