From mboxrd@z Thu Jan 1 00:00:00 1970 From: Masami Hiramatsu Date: Wed, 24 Mar 2021 23:47:41 +0000 Subject: Re: [PATCH -tip v4 10/12] x86/kprobes: Push a fake return address at kretprobe_trampoline Message-Id: <20210325084741.74bdb2b1d2ed00fe68840cea@kernel.org> List-Id: References: <161639518354.895304.15627519393073806809.stgit@devnote2> <161639530062.895304.16962383429668412873.stgit@devnote2> <20210323223007.GG4746@worktop.programming.kicks-ass.net> <20210324104058.7c06aaeb0408e24db6ba46f8@kernel.org> <20210324160143.wd43zribpeop2czn@treble> In-Reply-To: <20210324160143.wd43zribpeop2czn@treble> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Josh Poimboeuf Cc: Peter Zijlstra , Steven Rostedt , Ingo Molnar , X86 ML , Daniel Xu , linux-kernel@vger.kernel.org, bpf@vger.kernel.org, kuba@kernel.org, mingo@redhat.com, ast@kernel.org, tglx@linutronix.de, kernel-team@fb.com, yhs@fb.com, linux-ia64@vger.kernel.org, Abhishek Sagar On Wed, 24 Mar 2021 11:01:43 -0500 Josh Poimboeuf wrote: > On Wed, Mar 24, 2021 at 10:40:58AM +0900, Masami Hiramatsu wrote: > > On Tue, 23 Mar 2021 23:30:07 +0100 > > Peter Zijlstra wrote: > > > > > On Mon, Mar 22, 2021 at 03:41:40PM +0900, Masami Hiramatsu wrote: > > > > ".global kretprobe_trampoline\n" > > > > ".type kretprobe_trampoline, @function\n" > > > > "kretprobe_trampoline:\n" > > > > #ifdef CONFIG_X86_64 > > > > > > So what happens if we get an NMI here? That is, after the RET but before > > > the push? Then our IP points into the trampoline but we've not done that > > > push yet. > > > > Not only NMI, but also interrupts can happen. There is no cli/sti here. > > > > Anyway, thanks for pointing! > > I think in UNWIND_HINT_TYPE_REGS and UNWIND_HINT_TYPE_REGS_PARTIAL cases > > ORC unwinder also has to check the state->ip and if it is kretprobe_trampoline, > > it should be recovered. > > What about this? > > I think the REGS and REGS_PARTIAL cases can also be affected by function > graph tracing. So should they use the generic unwind_recover_ret_addr() > instead of unwind_recover_kretprobe()? Yes, but I'm not sure this parameter can be applied. For example, it passed "state->sp - sizeof(unsigned long)" as where the return address stored address. Is that same on ftrace graph too? Thank you, -- Masami Hiramatsu