Re: linux-next: build warnings after merge of the tip tree

Peter Zijlstra
2022-03-22T08:09:07Z

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?

I'm thinking you want a copy of __KERNEL_DS in that stack slot, not a
function pointer.