On Tue, 22 Mar 2022 09:08:22 +0100 Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > On Tue, Mar 22, 2022 at 02:31:36PM +0900, Masami Hiramatsu wrote: > > > > Also, I think both should fix regs->ss. > > > > I'm not sure this part. Since the return trampoline should run in the same > > context of the called function, isn't ss same there too? > > It creates pt_regs on the stack, so the trampolines do: > > push $arch_rethook_trampoline > push %rsp > pushf > sub $24, %rsp /* cs, ip, orig_ax */ > push %rdi > ... > push %r15 > > That means that if anybody looks at regs->ss, it'll find > $arch_rethook_trampoline, which isn't a valid segment descriptor, or am > I just really bad at counting today? Ah, got it. It seems that the ss was skipped from the beginning, and no one argued that. > I'm thinking you want a copy of __KERNEL_DS in that stack slot, not a > function pointer. The function pointer is for unwinding stack which involves the kretprobe. Anyway, I can add a slot for ss if it is neeeded. But if it always be __KERNEL_DS, is it worth to save it? Thank you, -- Masami Hiramatsu <mhiramat@xxxxxxxxxx>
