On Wed, Jan 18, 2023 at 02:41:00PM -0500, Gregory Price wrote: > ---------- Forwarded message --------- > From: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Date: Wed, Jan 18, 2023 at 12:16 PM > Subject: Re: [PATCH 1/3] ptrace,syscall_user_dispatch: Implement Syscall > User Dispatch Suspension > To: Gregory Price <gourry.memverge@xxxxxxxxx> > > > On Mon, Jan 09, 2023 at 10:33:46AM -0500, Gregory Price wrote: > > @@ -36,6 +37,10 @@ bool syscall_user_dispatch(struct pt_regs *regs) > > struct syscall_user_dispatch *sd = ¤t->syscall_dispatch; > > char state; > > > > + if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) && > > + unlikely(current->ptrace & > PT_SUSPEND_SYSCALL_USER_DISPATCH)) > > + return false; > > + > > if (likely(instruction_pointer(regs) - sd->offset < sd->len)) > > return false; > > > > So by making syscall_user_dispatch() return false, we'll make > syscall_trace_enter() continue to handle things, and supposedly you want > to land in ptrace_report_syscall_entry(), right? > > ... snip ... > > Should setting this then not also depend on having > SYSCALL_WORK_SYSCALL_TRACE set? Because without that, you get 'funny' > things. Hm, this is an interesting question. My thoughts are that I want the process to handle the syscall as-if syscall user dispatch was not present at all, regardless of SYSCALL_TRACE. This is because some software, like CRIU, actually injects syscalls to run in the context of the software in an effort to collect resources. So I actually *want* those 'funny' things to occur, because they're most likely intentional. I don't necessarily want to intercept system calls that subsequently occur (although i might). So if this feature required SYSCALL_TRACE, you would no longer be able to inject system calls ala CRIU. That's also my understanding of the SECCOMP_SUSPEND feature as well, it's intended specifically to allow *otherwise disallowed* syscalls to be injected into the process and SECCOMP bypassed. (in this case, SECCOMP_SUSPEND requires root for exactly this reason).
