[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAHk-=wjZDhwStWvioV7totCnZfp74bqH0y1UJxkmFfdLg48wDA@mail.gmail.com>
Date: Fri, 3 May 2019 16:16:58 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Andy Lutomirski <luto@...capital.net>
Cc: Steven Rostedt <rostedt@...dmis.org>,
Peter Zijlstra <peterz@...radead.org>,
Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Andy Lutomirski <luto@...nel.org>,
Nicolai Stange <nstange@...e.de>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>,
"the arch/x86 maintainers" <x86@...nel.org>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Jiri Kosina <jikos@...nel.org>,
Miroslav Benes <mbenes@...e.cz>,
Petr Mladek <pmladek@...e.com>,
Joe Lawrence <joe.lawrence@...hat.com>,
Shuah Khan <shuah@...nel.org>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Mimi Zohar <zohar@...ux.ibm.com>,
Juergen Gross <jgross@...e.com>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Nayna Jain <nayna@...ux.ibm.com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
Joerg Roedel <jroedel@...e.de>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@...r.kernel.org>, stable <stable@...r.kernel.org>
Subject: Re: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions
On Fri, May 3, 2019 at 3:55 PM Andy Lutomirski <luto@...capital.net> wrote:
>
> But I think this will end up worse than the version where the entry code fixes it up. This is because, if the C code moves pt_regs, then we need some way to pass the new pointer back to the asm.
What? I already posted that code. Let me quote it again:
Message-ID: <CAHk-=wh8bi5c_GkyjPtDAiaXaZRqtmhWs30usUvs4qK_F+c9tg@...l.gmail.com>
# args: pt_regs pointer (no error code for int3)
movl %esp,%eax
# allocate a bit of extra room on the stack, so that
# 'kernel_int3' can move the pt_regs
subl $8,%esp
call kernel_int3
movl %eax,%esp
It's that easy (this is with the assumption that we've already applied
the "standalone simple int3" case, but I think the above might work
even with the current code model, just the "call do_int3" needs to
have the kernel/not-kernel distinction and do the above for the kernel
case)
That's *MUCH* easier than your code to move entries around on the
stack just as you return, and has the advantage of not changing any
C-visible layout.
The C interface looks like this
/* Note: on x86-32, we can move 'regs' around for push/pop emulation */
struct pt_regs *kernel_int3(struct pt_regs *regs)
{
..
.. need to pass regs to emulation functions
.. and call emulation needs to return it
..
return regs;
}
and I just posted as a response to Stephen the *trivial* do_int3()
wrapper (so that x86-64 doesn't need to care), and the *trivial* code
to actually emulate a call instruction.
And when I say "trivial", I obviously mean "totally untested and
probably buggy", but it sure seems *simple*.,
Notice? Simple and minimal changes to entry code that only affect
int3, and nothing else.
Linus
Powered by blists - more mailing lists