linux-kernel - Re: [PATCH v5 21/27] x86/ftrace: Adapt function tracing for PIE support

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Date:   Tue, 26 Jun 2018 11:21:10 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Thomas Garnier <thgarnie@...gle.com>
Cc:     kernel-hardening@...ts.openwall.com,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        James Hogan <jhogan@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        nixiaoming <nixiaoming@...wei.com>,
        Guenter Roeck <linux@...ck-us.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 21/27] x86/ftrace: Adapt function tracing for PIE
 support

On Mon, 25 Jun 2018 15:39:09 -0700
Thomas Garnier <thgarnie@...gle.com> wrote:

> When using PIE with function tracing, the compiler generates a
> call through the GOT (call *__fentry__@...PCREL). This instruction
> takes 6-bytes instead of 5-bytes with a relative call.
> 
> If PIE is enabled, replace the 6th byte of the GOT call by a 1-byte nop
> so ftrace can handle the previous 5-bytes as before.
> 
> Position Independent Executable (PIE) support will allow to extend the
> KASLR randomization range 0xffffffff80000000.
> 
> Signed-off-by: Thomas Garnier <thgarnie@...gle.com>

Thanks for doing it this way.

Reviewed-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve