On Thu, Jan 16, 2025 at 01:07:59PM -0800, Charlie Jenkins wrote: > On Thu, Jan 16, 2025 at 10:33:28AM +0200, Dmitry V. Levin wrote: > > On Wed, Jan 15, 2025 at 05:55:31PM -0800, Charlie Jenkins wrote: > > > On Mon, Jan 13, 2025 at 07:12:08PM +0200, Dmitry V. Levin wrote: > > [...] > > > > + /* Changing the type of the system call stop is not supported. */ > > > > + if (ptrace_get_syscall_info_op(child) != info.op) > > > > > > Since this isn't supported anyway, would it make sense to set the > > > info.op to ptrace_get_syscall_info_op(child) like is done for > > > get_syscall_info? The usecase I see for this is simplifying when the > > > user doesn't call PTRACE_GET_SYSCALL_INFO before calling > > > PTRACE_SET_SYSCALL_INFO. > > > > struct ptrace_syscall_info.op is a field that specifies how to interpret > > the union fields of the structure, so if "op" is ignored, then the > > kernel would infer the meaning of the structure specified by the userspace > > tracer from the kernel state of the tracee. This looks a bit too > > error-prone to allow. For example, nothing good is expected to happen > > if syscall entry information is applied in a syscall exit stop. > > Yes that's a good point. > > > > > The tracer is not obliged to call PTRACE_GET_SYSCALL_INFO to set > > struct ptrace_syscall_info.op. If the tracer keeps track of ptrace stops > > by other means, it can assign the right value by itself. > > > > And, btw, the comment should say "is not currently supported", > > I'll update it in the next iteration. > > > > An idea mentioned in prior discussions was that it would make sense to > > specify syscall return value along with skipping the syscall in seccomp stop, > > and this would require a different value for "op" field, but > > I decided not to introduce this extra complexity yet. > > Makes sense, thank you! > > - Charlie I am no longer convinced that we need Celeste's patch that solves this problem on riscv [1]. That patch is necessary without this change, but PTRACE_SET_SYSCALL_INFO seems like a cleaner solution. Reviewed-by: Charlie Jenkins <charlie@xxxxxxxxxxxx> Tested-by: Charlie Jenkins <charlie@xxxxxxxxxxxx> - Charlie [1] https://lore.kernel.org/lkml/20250115-13cc73c36c7bb3b9f046f614@orel/T/ > > > > > > > -- > > ldv
