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Re: [PATCH 1/1] stackleak: Register the 'stackleak_cleanup' pass before the 'mach' pass
- From: Alexander Popov <alex dot popov at linux dot com>
- To: Kees Cook <keescook at chromium dot org>
- Cc: Kernel Hardening <kernel-hardening at lists dot openwall dot com>, Jann Horn <jannh at google dot com>, Andy Lutomirski <luto at kernel dot org>, Borislav Petkov <bp at alien8 dot de>, Thomas Gleixner <tglx at linutronix dot de>, Dave Hansen <dave dot hansen at linux dot intel dot com>, Steven Rostedt <rostedt at goodmis dot org>, Peter Zijlstra <peterz at infradead dot org>, Masami Hiramatsu <mhiramat at kernel dot org>, Florian Weimer <fweimer at redhat dot com>, Richard Sandiford <richard dot sandiford at arm dot com>, Segher Boessenkool <segher at kernel dot crashing dot org>, amonakov at ispras dot ru, Tycho Andersen <tycho at tycho dot ws>, Laura Abbott <labbott at redhat dot com>, Mark Rutland <mark dot rutland at arm dot com>, Emese Revfy <re dot emese at gmail dot com>, Thomas Garnier <thgarnie at google dot com>, Ingo Molnar <mingo at kernel dot org>, Will Deacon <will dot deacon at arm dot com>, Alexei Starovoitov <ast at kernel dot org>, Ard Biesheuvel <ard dot biesheuvel at linaro dot org>, "H. Peter Anvin" <hpa at zytor dot com>, "David S. Miller" <davem at davemloft dot net>, linux-arm-kernel <linux-arm-kernel at lists dot infradead dot org>, gcc at gcc dot gnu dot org, LKML <linux-kernel at vger dot kernel dot org>
- Date: Mon, 3 Dec 2018 21:25:01 +0300
- Subject: Re: [PATCH 1/1] stackleak: Register the 'stackleak_cleanup' pass before the 'mach' pass
- References: <email@example.com> <CAGXu5jJ7LmHRJJxtH2HD4XEu5hPLtAe=koJbaCmqF9qoSw=sVw@mail.gmail.com> <CAGXu5jKcRLcAg7r-E-9LMjK0YisLJp2TVYoiBwE+4ctYzi5wkg@mail.gmail.com>
- Reply-to: alex dot popov at linux dot com
On 30.11.2018 20:12, Kees Cook wrote:
> On Fri, Nov 30, 2018 at 9:09 AM Kees Cook <firstname.lastname@example.org> wrote:
>> On Fri, Nov 30, 2018 at 5:20 AM Alexander Popov <email@example.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 <firstname.lastname@example.org>
>>> Signed-off-by: Alexander Popov <email@example.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. */
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.