linux-kernel - Re: [PATCH v2] tracing: Add test for user space strings when filtering on string pointers

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Date:   Thu, 13 Jan 2022 16:51:15 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Sven Schnelle <svens@...ux.ibm.com>
Cc:     David Laight <David.Laight@...LAB.COM>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pingfan Liu <kernelfans@...il.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Tom Zanussi <zanussi@...nel.org>, hca@...ux.ibm.com,
        deller@....de
Subject: Re: [PATCH v2] tracing: Add test for user space strings when
 filtering on  string pointers

On Thu, 13 Jan 2022 22:28:01 +0100
Sven Schnelle <svens@...ux.ibm.com> wrote:
> 
> Hmm, i don't see how. On s390, TASK_SIZE is -PAGE_SIZE, which means
> 0xfffffffffffff000 so i think the if() condition below is always true.

Yes, I did that to just use the kernel version and not the user space one.

This is just a workaround for now.

> 
> Too bad that the __user attribute is stripped during a normal compile.
> But couldn't we add the information whether a pointer belongs to user
> or kernel space in the trace event definition? For syscall tracing it's
> easy, because pointer types in SYSCALL_DEFINE() and friends are always
> userspace pointers?

We could add something later. As it is currently the merge window, and this
is a real bug, I'm going to just leave it as is, and we can work to fix the
other archs later. I need to get a pull request ready by tomorrow.

-- Steve