Re: [PATCH v3 3/3] x86/ptrace, x86/signal: Remove TS_I386_REGS_POKED

Oleg Nesterov
2016-06-23T21:25:31Z

Again, I think the patch is fine, just a question

On 06/20, Andy Lutomirski wrote:
>
> System call restart has some oddities wrt ptrace:
>
> 1. For whatever reason, the kernel delivers signals and triggers
> ptrace before handling syscall restart. This means that
> -ERESTART_RESTARTBLOCK, etc is visible to userspace. We could
> plausibly get away with changing that, but it seems quite risky.

How we can change this?

The kernel simply can't know how it should react to (say) -ERESTARTSYS
until debugger acks/nacks/changes the signal reported by tracee.

> + /*
> + * A 32-bit ptracer has the following expectations:
> + *
> + * - Storing -1 (i.e. 0xffffffff) to orig_eax will prevent
> + * syscall restart handling.
> + *
> + * - Restoring regs saved on exit from an interrupted
> + * restartable syscall will trigger syscall restart. Such
> + * regs will have non-negative orig_eax and negative eax.
> + *
> + * The kernel's syscall restart code treats regs->orig_ax and
> + * regs->ax as 64-bit signed quantities. 32-bit user code
> + * doesn't care about the high bits. Keep it simple and just
> + * sign-extend both values.
> + */
> + R32_SIGNED(orig_eax, orig_ax);
> + R32_SIGNED(eax, ax);

OK. but do we really need R32_SIGNED(orig_eax) ? syscall_get_nr()
returns "int", not "long".

Oleg.