linux-kernel - Re: [kernel-hardening] [RFC V2 2/6] lib: vsprintf: whitelist stack traces

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Message-ID: <20171002214942.GA11207@eros>
Date:   Tue, 3 Oct 2017 08:49:42 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     Will Deacon <will.deacon@....com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Petr Mladek <pmladek@...e.com>, Joe Perches <joe@...ches.com>,
        Ian Campbell <ijc@...lion.org.uk>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        William Roberts <william.c.roberts@...el.com>,
        Chris Fries <cfries@...gle.com>,
        Dave Weinstein <olorin@...gle.com>
Subject: Re: [kernel-hardening] [RFC V2 2/6] lib: vsprintf: whitelist stack
 traces

On Mon, Oct 02, 2017 at 11:42:05AM +0100, Will Deacon wrote:
> On Sun, Oct 01, 2017 at 11:06:46AM +1100, Tobin C. Harding wrote:
> > Use the %pP functionality to explicitly allow kernel
> > pointers to be logged for stack traces.
> > 
> > Signed-off-by: Tobin C. Harding <me@...in.cc>
> > ---
> >  arch/arm64/kernel/traps.c | 4 ++--
> >  kernel/printk/printk.c    | 2 +-
> >  2 files changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
> > index 5ea4b85..fe09660 100644
> > --- a/arch/arm64/kernel/traps.c
> > +++ b/arch/arm64/kernel/traps.c
> > @@ -147,7 +147,7 @@ void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
> >  	struct stackframe frame;
> >  	int skip;
> >  
> > -	pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);
> > +	pr_debug("%s(regs = %pP tsk = %pP)\n", __func__, regs, tsk);
> 
> Why do we care for pr_debug?

Thanks for the review Will. I did not do the original work on this series so do not know the
original intent behind this change. I tend to agree with your comment. Will remove this change for
v3.

> >  	if (!tsk)
> >  		tsk = current;
> > @@ -233,7 +233,7 @@ static int __die(const char *str, int err, struct pt_regs *regs)
> >  
> >  	print_modules();
> >  	__show_regs(regs);
> > -	pr_emerg("Process %.*s (pid: %d, stack limit = 0x%p)\n",
> > +	pr_emerg("Process %.*s (pid: %d, stack limit = 0x%pP)\n",
> >  		 TASK_COMM_LEN, tsk->comm, task_pid_nr(tsk),
> >  		 end_of_stack(tsk));
> >  
> > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> > index 512f7c2..af0bc8e 100644
> > --- a/kernel/printk/printk.c
> > +++ b/kernel/printk/printk.c
> 
> It probably makes sense to keep this separate from arch/ changes

Point noted.

thanks,
Tobin.