Andy Lutomirski <luto@xxxxxxxxxxxxxx> writes: >> On May 29, 2020, at 11:00 PM, Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx> wrote: >> >> Modern Windows applications are executing system call instructions >> directly from the application's code without going through the WinAPI. >> This breaks Wine emulation, because it doesn't have a chance to >> intercept and emulate these syscalls before they are submitted to Linux. >> >> In addition, we cannot simply trap every system call of the application >> to userspace using PTRACE_SYSEMU, because performance would suffer, >> since our main use case is to run Windows games over Linux. Therefore, >> we need some in-kernel filtering to decide whether the syscall was >> issued by the wine code or by the windows application. > > Do you really need in-kernel filtering? What if you could have > efficient userspace filtering instead? That is, set something up so > that all syscalls, except those from a special address, are translated > to CALL thunk where the thunk is configured per task. Then the thunk > can do whatever emulation is needed. Hi, I suggested something similar to my customer, by using libsyscall-intercept. The idea would be overwritting the syscall instruction with a call to the entry point. I'm not a specialist on the specifics of Windows games, (cc'ed Paul Gofman, who can provide more details on that side), but as far as I understand, the reason why that is not feasible is that the anti-cheat protection in games will abort execution if the binary region was modified either on-disk or in-memory. Is there some mechanism to do that without modiyfing the application? > Getting the details and especially the interaction with any seccomp > filters that may be installed right could be tricky, but the performance > should be decent, at least on non-PTI systems. > > (If we go this route, I suspect that the correct interaction with > seccomp is that this type of redirection takes precedence over seccomp > and seccomp filters are not invoked for redirected syscalls. After all, > a redirected syscall is, functionally, not a syscall at all.) > -- Gabriel Krisman Bertazi
