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[2001:1ae9:1c2:4c00:726e:c10f:8833:ff22]) by smtp.gmail.com with ESMTPSA id s14-20020a05600c384e00b00413ee7921b4sm5001269wmr.15.2024.03.21.02.59.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 Mar 2024 02:59:37 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Thu, 21 Mar 2024 10:59:34 +0100 To: Oleg Nesterov Cc: Jiri Olsa , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , bpf@vger.kernel.org, Song Liu , Yonghong Song , John Fastabend , Peter Zijlstra , Thomas Gleixner , "Borislav Petkov (AMD)" , x86@kernel.org Subject: Re: [PATCH RFC bpf-next 4/3] uprobe: ensure sys_uretprobe uses sysret Message-ID: References: <20240318093139.293497-1-jolsa@kernel.org> <20240319102523.GC20287@redhat.com> <20240320143739.GA32579@redhat.com> <20240320152848.GA7613@redhat.com> Precedence: bulk X-Mailing-List: bpf@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: <20240320152848.GA7613@redhat.com> On Wed, Mar 20, 2024 at 04:28:48PM +0100, Oleg Nesterov wrote: SNIP > SYSCALL_DEFINE0(uretprobe) > { > struct pt_regs *regs = task_pt_regs(current); > unsigned long err, ip, sp, r11_cx_ax[3]; > > err = copy_from_user(r11_cx_ax, (void __user*)regs->sp, sizeof(r11_cx_ax)); > WARN_ON_ONCE(err); > > // Q1: apart from ax, do we really care? > // expose the "right" values of r11/cx/ax/sp to uprobe_consumer's > regs->r11 = r11_cx_ax[0]; > regs->cx = r11_cx_ax[1]; > regs->ax = r11_cx_ax[2]; > regs->sp += sizeof(r11_cx_ax); > regs->orig_ax = -1; > > ip = regs->ip; > sp = regs->sp; > > uprobe_handle_trampoline(regs); > > // Q2: is it possible? do we care? > // uprobe_consumer has changed sp, we can do nothing, > // just return via iret. > if (regs->sp != sp) > return regs->ax; > regs->sp -= sizeof(r11_cx_ax); > > // Q3: is it possible? do we care? > // for the case uprobe_consumer has changed r11/cx > r11_cx_ax[0] = regs->r11; > r11_cx_ax[1] = regs->cx; I wonder we could add test for this as well, and check we return proper register values in case the consuer changed them, will check > > // comment to explain this hack > r11_cx_ax[2] = regs->ip; > regs->ip = ip; we still need restore regs->ip in case do_syscall_64 decides to do iret for some reason, right? overall lgtm, thanks jirka > > err = copy_to_user((void __user*)regs->sp, r11_cx_ax, sizeof(r11_cx_ax)); > WARN_ON_ONCE(err); > > // ensure sysret, see do_syscall_64() > regs->r11 = regs->flags; > regs->cx = regs->ip; > > return regs->ax; > } > > Oleg. >