linux-hardening - Re: [PATCH v4 02/21] kallsyms: Export kallsyms_lookup

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Message-ID: <2023062852-jurist-sitcom-e0d6@gregkh>
Date:   Wed, 28 Jun 2023 17:43:25 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Will Deacon <will@...nel.org>
Cc:     Mukesh Ojha <quic_mojha@...cinc.com>,
        Pavan Kondeti <quic_pkondeti@...cinc.com>, corbet@....net,
        agross@...nel.org, andersson@...nel.org, konrad.dybcio@...aro.org,
        robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        conor+dt@...nel.org, keescook@...omium.org, tony.luck@...el.com,
        gpiccoli@...lia.com, mathieu.poirier@...aro.org,
        catalin.marinas@....com, linus.walleij@...aro.org,
        andy.shevchenko@...il.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-hardening@...r.kernel.org,
        linux-remoteproc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-gpio@...r.kernel.org
Subject: Re: [PATCH v4 02/21] kallsyms: Export kallsyms_lookup_name

On Wed, Jun 28, 2023 at 04:32:47PM +0100, Will Deacon wrote:
> On Wed, Jun 28, 2023 at 08:52:57PM +0530, Mukesh Ojha wrote:
> > 
> > 
> > On 6/28/2023 7:23 PM, Pavan Kondeti wrote:
> > > On Wed, Jun 28, 2023 at 06:04:29PM +0530, Mukesh Ojha wrote:
> > > > Module like minidump providing debugging support will need to
> > > > get the symbol information from the core kernel e.g to get
> > > > the linux_banner, kernel section addresses bss, data, ro etc.
> > > > 
> > > One might ask why we would need such a debug driver to
> > > be compiled as module? What would you do if we need to capture more
> > > kernel data structures later? Do you plan to continue use
> > > kallsyms_lookup_name() to query all the symbols?
> > 
> > You are on point, i needed this driver to be static but i don't have
> > any example at present to collect more than just _linux_banner_ from
> > my existing set of patches..
> > 
> > Agree, it will be easier to make this driver as static instead of
> > opening up the doors for modules to abuse via exporting
> > kallsyms_lookup_name() and also it will be very slow for production
> > kernel uses.
> 
> Right, I unexported that symbol deliberately in 0bd476e6c671 ("kallsyms:
> unexport kallsyms_lookup_name() and kallsyms_on_each_symbol()") and I
> don't think we should add it back for this driver.

I agree, it shouldn't be needed by any in-kernel module/driver.  If you
really want the name, look it up afterward in userspace :)

thanks,

greg k-h