Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Message-ID: <7f608c18250c509ff091990d4bb460846fae11a0.camel@buserror.net>
From:   Scott Wood <oss@buserror.net>
To:     Jason Yan <yanaijie@huawei.com>, Daniel Axtens <dja@axtens.net>,
        mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org,
        diana.craciun@nxp.com, christophe.leroy@c-s.fr,
        benh@kernel.crashing.org, paulus@samba.org, npiggin@gmail.com,
        keescook@chromium.org, kernel-hardening@lists.openwall.com,
        me@tobin.cc
Cc:     linux-kernel@vger.kernel.org, zhaohongjiang@huawei.com
Date:   Mon, 02 Mar 2020 02:47:13 -0600
In-Reply-To: <17658c2b-9eb8-cee9-e9a2-93d316a401b1@huawei.com>
References: <20200206025825.22934-1-yanaijie@huawei.com>
         <87tv3drf79.fsf@dja-thinkpad.axtens.net>
         <8171d326-5138-4f5c-cff6-ad3ee606f0c2@huawei.com>
         <e8cd8f287934954cfa07dcf76ac73492e2d49a5b.camel@buserror.net>
         <dd8db870-b607-3f74-d3bc-a8d9f33f9852@huawei.com>
         <4c0e7fec63dbc7b91fa6c24692c73c256c131f51.camel@buserror.net>
         <188971ed-f1c4-39b3-c07e-89cc593d88d7@huawei.com>
         <530c49dfd97c811dc53ffc78c594d7133f7eb1e9.camel@buserror.net>
         <35e6c660-3896-bdb8-45f3-c1504aa2171f@huawei.com>
         <31b5966ba579ef246176a7d8ad18c2c02788dd27.camel@buserror.net>
         <17658c2b-9eb8-cee9-e9a2-93d316a401b1@huawei.com>
Organization: Red Hat
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 8bit
Subject: Re: [PATCH v3 0/6] implement KASLR for powerpc/fsl_booke/64
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Mon, 2020-03-02 at 15:12 +0800, Jason Yan wrote:
> 
> 在 2020/3/2 11:24, Scott Wood 写道:
> > On Mon, 2020-03-02 at 10:17 +0800, Jason Yan wrote:
> > > 
> > > 在 2020/3/1 6:54, Scott Wood 写道:
> > > > On Sat, 2020-02-29 at 15:27 +0800, Jason Yan wrote:
> > > > > 
> > > > > Turnning to %p may not be a good idea in this situation. So
> > > > > for the REG logs printed when dumping stack, we can disable it when
> > > > > KASLR is open. For the REG logs in other places like show_regs(),
> > > > > only
> > > > > privileged can trigger it, and they are not combind with a symbol,
> > > > > so
> > > > > I think it's ok to keep them.
> > > > > 
> > > > > diff --git a/arch/powerpc/kernel/process.c
> > > > > b/arch/powerpc/kernel/process.c
> > > > > index fad50db9dcf2..659c51f0739a 100644
> > > > > --- a/arch/powerpc/kernel/process.c
> > > > > +++ b/arch/powerpc/kernel/process.c
> > > > > @@ -2068,7 +2068,10 @@ void show_stack(struct task_struct *tsk,
> > > > > unsigned
> > > > > long *stack)
> > > > >                    newsp = stack[0];
> > > > >                    ip = stack[STACK_FRAME_LR_SAVE];
> > > > >                    if (!firstframe || ip != lr) {
> > > > > -                       printk("["REG"] ["REG"] %pS", sp, ip, (void
> > > > > *)ip);
> > > > > +                       if (IS_ENABLED(CONFIG_RANDOMIZE_BASE))
> > > > > +                               printk("%pS", (void *)ip);
> > > > > +                       else
> > > > > +                               printk("["REG"] ["REG"] %pS", sp,
> > > > > ip,
> > > > > (void *)ip);
> > > > 
> > > > This doesn't deal with "nokaslr" on the kernel command line.  It also
> > > > doesn't
> > > > seem like something that every callsite should have to opencode,
> > > > versus
> > > > having
> > > > an appropriate format specifier behaves as I described above (and I
> > > > still
> > > > don't see why that format specifier should not be "%p").
> > > > 
> > > 
> > > Actually I still do not understand why we should print the raw value
> > > here. When KALLSYMS is enabled we have symbol name  and  offset like
> > > put_cred_rcu+0x108/0x110, and when KALLSYMS is disabled we have the raw
> > > address.
> > 
> > I'm more concerned about the stack address for wading through a raw stack
> > dump
> > (to find function call arguments, etc).  The return address does help
> > confirm
> > that I'm on the right stack frame though, and also makes looking up a line
> > number slightly easier than having to look up a symbol address and then
> > add
> > the offset (at least for non-module addresses).
> > 
> > As a random aside, the mismatch between Linux printing a hex offset and
> > GDB
> > using decimal in disassembly is annoying...
> > 
> 
> OK, I will send a RFC patch to add a new format specifier such as "%pk" 
> or change the exsiting "%pK" to print raw value of addresses when KASLR 
> is disabled and print hash value of addresses when KASLR is enabled. 
> Let's see what the printk guys would say :)

I'm not sure that a new format specifier is needed versus changing the
behavior of "%p", and "%pK" definitely doesn't seem suitable given that it's
intended to be more restricted than "%p" (see commit ef0010a30935de4).  The
question is whether there is a legitimate reason to hash in the absence of
kaslr.

-Scott