From mboxrd@z Thu Jan  1 00:00:00 1970
From: peterz at infradead.org (Peter Zijlstra)
Date: Fri, 10 May 2019 14:31:31 +0200
Subject: [PATCH 2/4] x86/kprobes: Fix frame pointer annotations
In-Reply-To: <20190510135831.c4ad309c68fc254f819194fc@kernel.org>
References: <20190508115416.nblx7c2kocidpytm@treble>
 <20190508120416.GL2589@hirez.programming.kicks-ass.net>
 <20190508124248.u5ukpbhnh4wpiccq@treble>
 <20190508153907.GM2589@hirez.programming.kicks-ass.net>
 <20190508184848.qerg3flv3ej3xsev@treble>
 <20190509102030.dfa62e058f09d0d8cbdd6053@kernel.org>
 <20190509081431.GO2589@hirez.programming.kicks-ass.net>
 <20190509230106.3551b08553440d125e437f66@kernel.org>
 <20190509171416.GY2623@hirez.programming.kicks-ass.net>
 <20190510135831.c4ad309c68fc254f819194fc@kernel.org>
Message-ID: <20190510123131.GU2589@hirez.programming.kicks-ass.net>

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 at infradead.org> wrote:

> > Ideally also the optimized kprobe trampoline, but I've not managed to
> > fully comprehend that one.
> 
> As you pointed in other reply, save/restore can be a macro, but
> each trampoline code is slightly different. Optprobe template has
> below parts
> 
> (jumped from probed address)
> [store regs]
> [setup function arguments (pt_regs and probed address)]
> [handler call]
> [restore regs]
> [execute copied instruction]

 instruction_s_ ?

The JMP to this trampoline is likely 5 bytes and could have clobbered
multiple instructions, we'd then have to place them all here, and

> [jump back to probed address]

jump to after whatever instructions were clobbered by the JMP.

> Note that there is a limitation that if it is optiomized probe, user
> handler can not change regs->ip. (we can not use "ret" after executed
> a copied instruction, which must run on same stack)

Changing regs->ip in this case is going to be massively dodgy indeed :-)
But so would changing much else; changing stack layout would also be
somewhat tricky.

From mboxrd@z Thu Jan  1 00:00:00 1970
From: peterz@infradead.org (Peter Zijlstra)
Date: Fri, 10 May 2019 14:31:31 +0200
Subject: [PATCH 2/4] x86/kprobes: Fix frame pointer annotations
In-Reply-To: <20190510135831.c4ad309c68fc254f819194fc@kernel.org>
References: <20190508115416.nblx7c2kocidpytm@treble>
 <20190508120416.GL2589@hirez.programming.kicks-ass.net>
 <20190508124248.u5ukpbhnh4wpiccq@treble>
 <20190508153907.GM2589@hirez.programming.kicks-ass.net>
 <20190508184848.qerg3flv3ej3xsev@treble>
 <20190509102030.dfa62e058f09d0d8cbdd6053@kernel.org>
 <20190509081431.GO2589@hirez.programming.kicks-ass.net>
 <20190509230106.3551b08553440d125e437f66@kernel.org>
 <20190509171416.GY2623@hirez.programming.kicks-ass.net>
 <20190510135831.c4ad309c68fc254f819194fc@kernel.org>
Message-ID: <20190510123131.GU2589@hirez.programming.kicks-ass.net>
Content-Type: text/plain; charset="UTF-8"
Message-ID: <20190510123131.LlyYWhQfXB_5NuG8fHKLyu8Mhu4oF2LxrjnVdHDYTfQ@z>

On Fri, May 10, 2019@01:58:31PM +0900, Masami Hiramatsu wrote:
> On Thu, 9 May 2019 19:14:16 +0200
> Peter Zijlstra <peterz@infradead.org> wrote:

> > Ideally also the optimized kprobe trampoline, but I've not managed to
> > fully comprehend that one.
> 
> As you pointed in other reply, save/restore can be a macro, but
> each trampoline code is slightly different. Optprobe template has
> below parts
> 
> (jumped from probed address)
> [store regs]
> [setup function arguments (pt_regs and probed address)]
> [handler call]
> [restore regs]
> [execute copied instruction]

 instruction_s_ ?

The JMP to this trampoline is likely 5 bytes and could have clobbered
multiple instructions, we'd then have to place them all here, and

> [jump back to probed address]

jump to after whatever instructions were clobbered by the JMP.

> Note that there is a limitation that if it is optiomized probe, user
> handler can not change regs->ip. (we can not use "ret" after executed
> a copied instruction, which must run on same stack)

Changing regs->ip in this case is going to be massively dodgy indeed :-)
But so would changing much else; changing stack layout would also be
somewhat tricky.