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

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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.

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[PATCH 1/1] get_nr_restart_syscall() should return  __NR_ia32_restart_syscall if __USER32_CS Oleg Nesterov <oleg@redhat.com> - 2017-03-28 17:10 +0200
  Re: [PATCH 1/1] get_nr_restart_syscall() should return  __NR_ia32_restart_syscall if __USER32_CS Andy Lutomirski <luto@kernel.org> - 2017-03-28 17:10 +0200
    Re: [PATCH 1/1] get_nr_restart_syscall() should return  __NR_ia32_restart_syscall if __USER32_CS Oleg Nesterov <oleg@redhat.com> - 2017-03-28 18:30 +0200
      Re: [PATCH 1/1] get_nr_restart_syscall() should return  __NR_ia32_restart_syscall if __USER32_CS Andy Lutomirski <luto@amacapital.net> - 2017-03-28 19:20 +0200
      Re: [PATCH 1/1] get_nr_restart_syscall() should return  __NR_ia32_restart_syscall if __USER32_CS Oleg Nesterov <oleg@redhat.com> - 2017-03-29 17:10 +0200
        Re: [PATCH 1/1] get_nr_restart_syscall() should return  __NR_ia32_restart_syscall if __USER32_CS Andy Lutomirski <luto@amacapital.net> - 2017-03-29 19:10 +0200
          Re: [PATCH 1/1] get_nr_restart_syscall() should return  __NR_ia32_restart_syscall if __USER32_CS Oleg Nesterov <oleg@redhat.com> - 2017-03-30 17:30 +0200
            Re: [PATCH 1/1] get_nr_restart_syscall() should return  __NR_ia32_restart_syscall if __USER32_CS Andy Lutomirski <luto@amacapital.net> - 2017-03-30 20:40 +0200

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