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[PATCH 5/6] x86/ptrace: down with test_thread_flag(TIF_IA32)

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As the task isn't executing at the moment of {GET,SET}REGS,
return regset that corresponds to code selector, rather than
value of TIF_IA32 flag.
I.e. if we ptrace i386 elf binary that has just changed it's
code selector to __USER_CS, than GET_REGS will return
full x86_64 register set.

Note, that this will work only if application has changed it's CS.
If the application does 32-bit syscall with __USER_CS, ptrace
will still return 64-bit register set. Which might be still confusing
for tools that expect TS_COMPACT to be exposed [1, 2].

So this this change should make PTRACE_GETREGSET more reliable and
this will be another step to drop TIF_{IA32,X32} flags.

[1]: https://sourceforge.net/p/strace/mailman/message/30471411/
[2]: https://lkml.org/lkml/2012/1/18/320

Cc: Andy Lutomirski <luto@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
---
 arch/x86/kernel/ptrace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 600edd225e81..a2612d06cf4b 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -1355,7 +1355,7 @@ void update_regset_xstate_info(unsigned int size, u64 xstate_mask)
 const struct user_regset_view *task_user_regset_view(struct task_struct *task)
 {
 #ifdef CONFIG_IA32_EMULATION
-	if (test_tsk_thread_flag(task, TIF_IA32))
+	if (!user_64bit_mode(task_pt_regs(task)))
 #endif
 #if defined CONFIG_X86_32 || defined CONFIG_IA32_EMULATION
 		return &user_x86_32_view;
-- 
2.8.2

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[PATCH 0/6] x86: 32-bit compatible C/R on x86_64 Dmitry Safonov <dsafonov@virtuozzo.com> - 2016-06-01 15:20 +0200
  [PATCH 5/6] x86/ptrace: down with test_thread_flag(TIF_IA32) Dmitry Safonov <dsafonov@virtuozzo.com> - 2016-06-01 15:20 +0200
    Re: [PATCH 5/6] x86/ptrace: down with test_thread_flag(TIF_IA32) Cyrill Gorcunov <gorcunov@gmail.com> - 2016-06-03 12:00 +0200
      Re: [PATCH 5/6] x86/ptrace: down with test_thread_flag(TIF_IA32) Cyrill Gorcunov <gorcunov@gmail.com> - 2016-06-03 12:50 +0200
    Re: [PATCH 5/6] x86/ptrace: down with test_thread_flag(TIF_IA32) Oleg Nesterov <oleg@redhat.com> - 2016-06-07 00:30 +0200
      Re: [PATCH 5/6] x86/ptrace: down with test_thread_flag(TIF_IA32) Dmitry Safonov <dsafonov@virtuozzo.com> - 2016-06-07 13:40 +0200
      Re: [PATCH 5/6] x86/ptrace: down with test_thread_flag(TIF_IA32) Andy Lutomirski <luto@amacapital.net> - 2016-06-09 19:30 +0200
        Re: [PATCH 5/6] x86/ptrace: down with test_thread_flag(TIF_IA32) Oleg Nesterov <oleg@redhat.com> - 2016-06-10 22:10 +0200
          Re: [PATCH 5/6] x86/ptrace: down with test_thread_flag(TIF_IA32) Andy Lutomirski <luto@amacapital.net> - 2016-06-10 22:20 +0200
  [PATCH 1/6] x86/vdso: unmap vdso blob on vvar mapping failure Dmitry Safonov <dsafonov@virtuozzo.com> - 2016-06-01 15:20 +0200
  [PATCH 3/6] x86/arch_prctl/vdso: add ARCH_MAP_VDSO_* Dmitry Safonov <dsafonov@virtuozzo.com> - 2016-06-01 15:20 +0200

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