linux-kernel - Re: [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access kernel memory that can fault

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Date:   Fri, 15 Feb 2019 21:21:33 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        stable <stable@...r.kernel.org>,
        Changbin Du <changbin.du@...il.com>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH 1/2 v2] kprobe: Do not use uaccess functions to access
 kernel memory that can fault

On Fri, 15 Feb 2019 18:14:21 -0800
Andy Lutomirski <luto@...capital.net> wrote:

> > In the uprobes case, we have:
> > 
> > static nokprobe_inline int
> > probe_mem_read(void *dest, void *src, size_t size)
> > {
> >    void __user *vaddr = (void __force __user *)src;
> > 
> >    return copy_from_user(dest, vaddr, size) ? -EFAULT : 0;
> > }
> > 
> > Because that is adding probes on userspace code.
> > 
> >   
> 
> Can the kprobe case call probe_kernel_read?  Maybe it does already?

Yes, the probe_mem_read() is only used in the trace_probe_tmpl.h which
for uprobes is the above "copy_from_user()" and for the kprobes case it
is probe_kernel_read().

-- Steve