lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  PHC 
Open Source and information security mailing list archives
Hash Suite for Android: free password hash cracker in your pocket
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:   Mon, 6 May 2019 23:21:58 -0400
From:   Steven Rostedt <>
To:     Linus Torvalds <>
Cc:     Peter Zijlstra <>,
        Andy Lutomirski <>,
        Linux List Kernel Mailing <>,
        Ingo Molnar <>,
        Andrew Morton <>,
        Andy Lutomirski <>,
        Nicolai Stange <>,
        Thomas Gleixner <>,
        Ingo Molnar <>, Borislav Petkov <>,
        "H. Peter Anvin" <>,
        "the arch/x86 maintainers" <>,
        Josh Poimboeuf <>,
        Jiri Kosina <>,
        Miroslav Benes <>,
        Petr Mladek <>,
        Joe Lawrence <>,
        Shuah Khan <>,
        Konrad Rzeszutek Wilk <>,
        Tim Chen <>,
        Sebastian Andrzej Siewior <>,
        Mimi Zohar <>,
        Juergen Gross <>,
        Nick Desaulniers <>,
        Nayna Jain <>,
        Masahiro Yamada <>,
        Joerg Roedel <>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <>, stable <>,
        Masami Hiramatsu <>
Subject: Re: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call

On Mon, 6 May 2019 20:05:24 -0700
Linus Torvalds <> wrote:

> It would emulate the call that has had its first byte overwritten by
> 'int3'. Without doing any lookups of what it was supposed to change
> the call to, because it simply depends on what the rewriting code is
> doing on another CPU (or on the same CPU - it wouldn't care).

OK, so this is just about what to have it call.

> So no need to look up anything, not at int3 time, and not at return
> time. It would just emulate the instruction atomically, with no state,
> and no need to look up what the 'ip' instruction is at the time.
> It could literally just use a single flag: "is ftrace updating call
> instructions". Add another flag for the "I'm nop'ing out call
> instructions" so that it knows to emulate a jump-over instead. That's
> it.

Well we have that, and we have to look up the record regardless to know
if this was a ftrace int3 or not (the ftrace_location(ip) does that).
And the record has a counter to # of attached callers. Zero being to
turn it into a nop.

Note, if we are going from nop to call or call to nop, it would need to
read the offset to see if it is a nop (don't want to call with the nop

> Because all the actual *values* would be entirely be determined by the
> actual rewriting that is going on independently of the 'int3'
> exception.

But still, we need to emulate the call, which requires pushing the
return code back onto the stack. I believe that part is the part we are
struggling with.

-- Steve

Powered by blists - more mailing lists