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From: Peter Zijlstra <peterz@infradead.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	linux-kernel@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andy Lutomirski <luto@kernel.org>,
	Nicolai Stange <nstange@suse.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, Jiri Kosina <jikos@kernel.org>,
	Miroslav Benes <mbenes@suse.cz>, Petr Mladek <pmladek@suse.com>,
	Joe Lawrence <joe.lawrence@redhat.com>,
	Shuah Khan <shuah@kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Mimi Zohar <zohar@linux.ibm.com>, Juergen Gross <jgross@suse.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Nayna Jain <nayna@linux.ibm.com>,
	Masahiro Yamada <yamada.masahiro@socionext.com>,
	Joerg Roedel <jroedel@suse.de>,
	linux-kselftest@vger.kernel.org
Subject: Re: [PATCH 2/4] x86/kprobes: Fix frame pointer annotations
Date: Mon, 13 May 2019 10:15:03 +0200	[thread overview]
Message-ID: <20190513081503.GK2623@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190511095655.405147cde331cd1da539d0e8@kernel.org>

On Sat, May 11, 2019 at 09:56:55AM +0900, Masami Hiramatsu wrote:
> On Fri, 10 May 2019 14:40:54 +0200
> Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > On Fri, May 10, 2019 at 01:58:31PM +0900, Masami Hiramatsu wrote:
> > > On Thu, 9 May 2019 19:14:16 +0200
> > > Peter Zijlstra <peterz@infradead.org> wrote:
> > > > > > --- a/arch/x86/kernel/kprobes/core.c
> > > > > > +++ b/arch/x86/kernel/kprobes/core.c
> > > > > > @@ -731,29 +731,8 @@ asm(
> > > > > >  	".global kretprobe_trampoline\n"
> > > > > >  	".type kretprobe_trampoline, @function\n"
> > > > > >  	"kretprobe_trampoline:\n"
> > 
> > > > > Here, we need a gap for storing ret-ip, because kretprobe_trampoline is
> > > > > the address which is returned from the target function. We have no 
> > > > > "ret-ip" here at this point. So something like
> > > > > 
> > > > > +	"push $0\n"	/* This is a gap, will be filled with real return address*/
> > > > 
> > > > The trampoline already provides a gap, trampoline_handler() will need to
> > > > use int3_emulate_push() if it wants to inject something on the return
> > > > stack.
> > > 
> > > I guess you mean the int3 case. This trampoline is used as a return destination.
> > 
> > > When the target function is called, kretprobe interrupts the first instruction,
> > > and replace the return address with this trampoline. When a "ret" instruction
> > > is done, it returns to this trampoline. Thus the stack frame start with
> > > previous context here. As you described above,
> > 
> > I would prefer to change that to inject an extra return address, instead
> > of replacing it. With the new exception stuff we can actually do that.
> > 
> > So on entry we then go from:
> > 
> > 	<previous context>
> > 	RET-IP
> > 
> > to
> > 
> > 	<previous context>
> > 	RET-IP
> > 	return-trampoline
> > 
> > So when the function returns, it falls into the trampoline instead.
> 
> Is that really possible? On x86-64, most parameters are passed by registers,
> but x86-32 (and x86-64 in rare case) some parameters can be passed by stack.
> If we change the stack layout in the function prologue, the code in
> function body can not access those parameters on stack.

Ooh, I see what you mean... yes that might be trouble indeed. Damn..

  reply	other threads:[~2019-05-13  8:15 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-08  7:49 [PATCH 0/4] x86: int3 fallout Peter Zijlstra
2019-05-08  7:49 ` [PATCH 1/4] x86/entry/32: Clean up return from interrupt preemption path Peter Zijlstra
2019-05-08  7:49 ` [PATCH 2/4] x86/kprobes: Fix frame pointer annotations Peter Zijlstra
2019-05-08 11:54   ` Josh Poimboeuf
2019-05-08 12:04     ` Peter Zijlstra
2019-05-08 12:40       ` Peter Zijlstra
2019-05-08 12:42       ` Josh Poimboeuf
2019-05-08 15:39         ` Peter Zijlstra
2019-05-08 18:48           ` Josh Poimboeuf
2019-05-09  1:20             ` Masami Hiramatsu
2019-05-09  8:14               ` Peter Zijlstra
2019-05-09  9:27                 ` Peter Zijlstra
2019-05-09 14:00                 ` Josh Poimboeuf
2019-05-09 14:01                 ` Masami Hiramatsu
2019-05-09 17:14                   ` Peter Zijlstra
2019-05-10  4:58                     ` Masami Hiramatsu
2019-05-10 12:31                       ` Peter Zijlstra
2019-05-11  0:52                         ` Masami Hiramatsu
2019-05-10 12:40                       ` Peter Zijlstra
2019-05-11  0:56                         ` Masami Hiramatsu
2019-05-13  8:15                           ` Peter Zijlstra [this message]
2019-05-09 16:20                 ` Andy Lutomirski
2019-05-09 17:18                   ` Peter Zijlstra
2019-05-09 17:43                   ` Steven Rostedt
2019-05-10  3:21                     ` Masami Hiramatsu
2019-05-10 12:14                       ` Peter Zijlstra
2019-05-10 12:17                       ` Peter Zijlstra
2019-05-10 14:54                         ` Steven Rostedt
2019-05-09 17:37                 ` Steven Rostedt
2019-05-09 18:26                   ` Peter Zijlstra
2019-05-09 18:36                     ` Steven Rostedt
2019-05-08  7:49 ` [PATCH 3/4] x86/ftrace: Add pt_regs frame annotations Peter Zijlstra
2019-05-08  7:49 ` [RFC][PATCH 4/4] x86_32: Provide consistent pt_regs Peter Zijlstra
2019-05-08 11:57   ` Josh Poimboeuf
2019-05-08 12:46     ` Ingo Molnar
2019-05-08 20:58   ` Linus Torvalds

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