On Tue, May 21, 2024 at 01:31:53AM +0000, Edgecombe, Rick P wrote: > On Mon, 2024-05-20 at 00:18 +0200, Jiri Olsa wrote: > > anyway I think we can fix that in another way by using the optimized > > trampoline, > > but returning to the user space through iret when shadow stack is detected > > (as I did in the first version, before you adjusted it to the sysret path). > > > > we need to update the return address on stack only when returning through the > > trampoline, but we can jump to original return address directly from syscall > > through iret.. which is slower, but with shadow stack we don't care > > > > basically the only change is adding the shstk_is_enabled check to the > > following condition in SYSCALL_DEFINE0(uretprobe): > > > > if (regs->sp != sp || shstk_is_enabled()) > > return regs->ax; > > On the surface it sounds reasonable. Thanks. > > And then I guess if tradeoffs are seen differently in the future, and we want to > enable the fast path for shadow stack we can go with your other solution. So > this just simply fixes things functionally without much code. yes, if we want to enable the fast path for shadow stack in future we'll need to remove that shstk_is_enabled and push extra frame on shadow stack jirka
