Re: [PATCH 1/1] get_nr_restart_syscall() should return __NR_ia32_restart_syscall if __USER32_CS

Andy Lutomirski
2017-03-28T15:04:29Z

On Tue, Mar 28, 2017 at 7:54 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> get_nr_restart_syscall() checks TS_I386_REGS_POKED but this bit is only
> set if debugger is 32-bit. If a 64-bit debugger restores the registers
> of a 32-bit debugee outside of syscall exit path get_nr_restart_syscall()
> wrongly returns __NR_restart_syscall.

I had sent a patch that introduced a new syscall nr, but it's not
quite safe because it could break seccomp-using programs. But your
patch here is also screwy.

How about we store the syscall arch to be restored in task_struct
along with restart_block? It's not perfect, but it should be 99% of
the way there without heuristics as nasty as yours.

--Andy

P.S. __USER32_CS is the wrong check even if we used your approach.
user_64bit_regs() is much better.