linux-kernel - [tip:x86/vdso] x86/ptrace: Down with test_thread_flag(TIF

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Date:   Wed, 14 Sep 2016 12:35:35 -0700
From:   tip-bot for Dmitry Safonov <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     hpa@...or.com, mingo@...nel.org, palves@...hat.com,
        tglx@...utronix.de, dsafonov@...tuozzo.com,
        linux-kernel@...r.kernel.org
Subject: [tip:x86/vdso] x86/ptrace: Down with test_thread_flag(TIF_IA32)

Commit-ID:  cc87324b3dbb9bdf6916c7f479230db24c4aa309
Gitweb:     http://git.kernel.org/tip/cc87324b3dbb9bdf6916c7f479230db24c4aa309
Author:     Dmitry Safonov <dsafonov@...tuozzo.com>
AuthorDate: Mon, 5 Sep 2016 16:33:07 +0300
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Wed, 14 Sep 2016 21:28:11 +0200

x86/ptrace: Down with test_thread_flag(TIF_IA32)

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

Signed-off-by: Dmitry Safonov <dsafonov@...tuozzo.com>
Cc: 0x7f454c46@...il.com
Cc: oleg@...hat.com
Cc: linux-mm@...ck.org
Cc: luto@...nel.org
Cc: Pedro Alves <palves@...hat.com>
Cc: gorcunov@...nvz.org
Cc: xemul@...tuozzo.com
Link: http://lkml.kernel.org/r/20160905133308.28234-6-dsafonov@virtuozzo.com
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

---
 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 f79576a..ad0bab8 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -1358,7 +1358,7 @@ 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;