Date: Mon, 3 Dec 2018 21:25:01 +0300 From: Alexander Popov <alex.popov@...ux.com> To: Kees Cook <keescook@...omium.org> Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>, Jann Horn <jannh@...gle.com>, Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...en8.de>, Thomas Gleixner <tglx@...utronix.de>, Dave Hansen <dave.hansen@...ux.intel.com>, Steven Rostedt <rostedt@...dmis.org>, Peter Zijlstra <peterz@...radead.org>, Masami Hiramatsu <mhiramat@...nel.org>, Florian Weimer <fweimer@...hat.com>, Richard Sandiford <richard.sandiford@....com>, Segher Boessenkool <segher@...nel.crashing.org>, amonakov@...ras.ru, Tycho Andersen <tycho@...ho.ws>, Laura Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>, Emese Revfy <re.emese@...il.com>, Thomas Garnier <thgarnie@...gle.com>, Ingo Molnar <mingo@...nel.org>, Will Deacon <will.deacon@....com>, Alexei Starovoitov <ast@...nel.org>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, "H. Peter Anvin" <hpa@...or.com>, "David S. Miller" <davem@...emloft.net>, linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>, gcc@....gnu.org, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 1/1] stackleak: Register the 'stackleak_cleanup' pass before the 'mach' pass On 30.11.2018 20:12, Kees Cook wrote: > On Fri, Nov 30, 2018 at 9:09 AM Kees Cook <keescook@...omium.org> wrote: >> >> On Fri, Nov 30, 2018 at 5:20 AM Alexander Popov <alex.popov@...ux.com> wrote: >>> >>> Currently the 'stackleak_cleanup' pass deleting a CALL insn is executed >>> after the 'reload' pass. That allows gcc to do some weird optimization in >>> function prologues and epilogues, which are generated later . >>> >>> Let's avoid that by registering the 'stackleak_cleanup' pass before >>> the 'mach' pass, which performs the machine dependent code transformations. >>> It's the moment when the stack frame size is final and function prologues >>> and epilogues are already generated. >>> >>>  https://www.openwall.com/lists/kernel-hardening/2018/11/23/2 >>> >>> Reported-by: kbuild test robot <lkp@...el.com> >>> Signed-off-by: Alexander Popov <alex.popov@...ux.com> >> >> Thanks, applied! > > Eek, no, this is breaking my build badly: > > *** WARNING *** there are active plugins, do not report this as a bug > unless you can reproduce it without enabling any plugins. > Event | Plugins > PLUGIN_START_UNIT | stackleak_plugin > kernel/exit.c: In function ‘release_task’: > kernel/exit.c:228:1: internal compiler error: Segmentation fault > } > > Failing with: > > gcc (Ubuntu 7.3.0-16ubuntu3) 7.3.0 I've done debugging of gcc with gdb and now understand my mistake. It turned out that I register the 'stackleak_cleanup' pass deleting CALL insn for that particular moment when the control flow graph is inconsistent. That's what the machine-specific reorg passes do on various architectures: /* We are freeing block_for_insn in the toplev to keep compatibility with old MDEP_REORGS that are not CFG based. Recompute it now. */ compute_bb_for_insn (); So recomputing basic block info for insns before calling delete_insn_and_edges() fixes the issue. But I think it's better to register the 'stackleak_cleanup' pass just one pass earlier -- before the '*free_cfg' pass. I'll double check it for different versions of gcc on all supported architectures and return with a new patch. Best regards, Alexander
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