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Mon, 28 Apr 2025 06:24:36 -0700 (PDT) Received: from krava ([173.38.220.34]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-5f7016f6424sm6011635a12.42.2025.04.28.06.24.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Apr 2025 06:24:35 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Mon, 28 Apr 2025 15:24:33 +0200 To: Oleg Nesterov Cc: Peter Zijlstra , Andrii Nakryiko , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, x86@kernel.org, Song Liu , Yonghong Song , John Fastabend , Hao Luo , Steven Rostedt , Masami Hiramatsu , Alan Maguire , David Laight , Thomas =?iso-8859-1?Q?Wei=DFschuh?= , Ingo Molnar Subject: Re: [PATCH perf/core 10/22] uprobes/x86: Add support to optimize uprobes Message-ID: References: <20250421214423.393661-1-jolsa@kernel.org> <20250421214423.393661-11-jolsa@kernel.org> <20250427171143.GA27775@redhat.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250427171143.GA27775@redhat.com> On Sun, Apr 27, 2025 at 07:11:43PM +0200, Oleg Nesterov wrote: SNIP > > +void arch_uprobe_optimize(struct arch_uprobe *auprobe, unsigned long vaddr) > > +{ > > + struct mm_struct *mm = current->mm; > > + uprobe_opcode_t insn[5]; > > + > > + /* > > + * Do not optimize if shadow stack is enabled, the return address hijack > > + * code in arch_uretprobe_hijack_return_addr updates wrong frame when > > + * the entry uprobe is optimized and the shadow stack crashes the app. > > + */ > > + if (shstk_is_enabled()) > > + return; > > Not sure I fully understand the comment/problem, but ... the issue is that sys_uprobe adjusts rsp to skip the uprobe trampoline stack frame (which is call + 3x push), so the uprobe consumers see expected stack then if we need to hijack the return address we: - update the return value on actual stack (updated rsp) - we update shadow stack with shstk_update_last_frame (last shadow stack frame) which will cause mismatch and the app crashes on trampoline's ret instruction I think we could make that work, but to make it simple I think it's better to skip it for now > what if > prctl(ARCH_SHSTK_ENABLE) is called after arch_uprobe_optimize() succeeds? so that would look like this: foo: [int3 -> call tramp] hijack foo's return address ... prctl(ARCH_SHSTK_ENABLE) ... prctl(ARCH_SHSTK_DISABLE) ret -> jumps to uretprobe trampoline at the time 'prctl(ARCH_SHSTK_ENABLE)' is called the return address is already hijacked/changed in any case IIUC you need to disable shadow stack before 'foo' returns thanks, jirka