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Date: Sun, 26 Jun 2016 17:23:00 -0700
From: Andy Lutomirski <luto@...capital.net>
To: Brian Gerst <brgerst@...il.com>
Cc: Andy Lutomirski <luto@...nel.org>, "the arch/x86 maintainers" <x86@...nel.org>, 
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-arch <linux-arch@...r.kernel.org>, 
	Borislav Petkov <bp@...en8.de>, Nadav Amit <nadav.amit@...il.com>, Kees Cook <keescook@...omium.org>, 
	"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, 
	Linus Torvalds <torvalds@...ux-foundation.org>, Josh Poimboeuf <jpoimboe@...hat.com>, 
	Jann Horn <jann@...jh.net>, Heiko Carstens <heiko.carstens@...ibm.com>
Subject: Re: [PATCH v4 22/29] x86/asm: Move 'status' from struct thread_info
 to struct thread_struct

On Sun, Jun 26, 2016 at 4:55 PM, Brian Gerst <brgerst@...il.com> wrote:
> On Sun, Jun 26, 2016 at 5:55 PM, Andy Lutomirski <luto@...nel.org> wrote:
>> Becuase sched.h and thread_info.h are a tangled mess, I turned
>> in_compat_syscall into a macro.  If we had current_thread_struct()
>> or similar and we could use it from thread_info.h, then this would
>> be a bit cleaner.
>>
>> Signed-off-by: Andy Lutomirski <luto@...nel.org>
>> ---
>>  arch/x86/entry/common.c            |  4 ++--
>>  arch/x86/include/asm/processor.h   | 12 ++++++++++++
>>  arch/x86/include/asm/syscall.h     | 23 +++++------------------
>>  arch/x86/include/asm/thread_info.h | 23 ++++-------------------
>>  arch/x86/kernel/asm-offsets.c      |  1 -
>>  arch/x86/kernel/fpu/init.c         |  1 -
>>  arch/x86/kernel/process_64.c       |  4 ++--
>>  arch/x86/kernel/ptrace.c           |  2 +-
>>  8 files changed, 26 insertions(+), 44 deletions(-)
>>
>> diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
>> index ec138e538c44..c4150bec7982 100644
>> --- a/arch/x86/entry/common.c
>> +++ b/arch/x86/entry/common.c
>> @@ -271,7 +271,7 @@ __visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
>>          * syscalls.  The fixup is exercised by the ptrace_syscall_32
>>          * selftest.
>>          */
>> -       ti->status &= ~TS_COMPAT;
>> +       current->thread.status &= ~TS_COMPAT;
>>  #endif
>>
>>         user_enter();
>> @@ -369,7 +369,7 @@ static __always_inline void do_syscall_32_irqs_on(struct pt_regs *regs)
>>         unsigned int nr = (unsigned int)regs->orig_ax;
>>
>>  #ifdef CONFIG_IA32_EMULATION
>> -       ti->status |= TS_COMPAT;
>> +       current->thread.status |= TS_COMPAT;
>>  #endif
>>
>>         if (READ_ONCE(ti->flags) & _TIF_WORK_SYSCALL_ENTRY) {
>> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
>> index a2e20d6d01fe..a75e720f6402 100644
>> --- a/arch/x86/include/asm/processor.h
>> +++ b/arch/x86/include/asm/processor.h
>> @@ -388,6 +388,9 @@ struct thread_struct {
>>         unsigned short          fsindex;
>>         unsigned short          gsindex;
>>  #endif
>> +
>> +       u32                     status;         /* thread synchronous flags */
>> +
>>  #ifdef CONFIG_X86_32
>>         unsigned long           ip;
>>  #endif
>> @@ -437,6 +440,15 @@ struct thread_struct {
>>  };
>>
>>  /*
>> + * Thread-synchronous status.
>> + *
>> + * This is different from the flags in that nobody else
>> + * ever touches our thread-synchronous status, so we don't
>> + * have to worry about atomic accesses.
>> + */
>> +#define TS_COMPAT              0x0002  /* 32bit syscall active (64BIT)*/
>> +
>> +/*
>>   * Set IOPL bits in EFLAGS from given mask
>>   */
>>  static inline void native_set_iopl_mask(unsigned mask)
>> diff --git a/arch/x86/include/asm/syscall.h b/arch/x86/include/asm/syscall.h
>> index 999b7cd2e78c..17229e7e2a1c 100644
>> --- a/arch/x86/include/asm/syscall.h
>> +++ b/arch/x86/include/asm/syscall.h
>> @@ -60,7 +60,7 @@ static inline long syscall_get_error(struct task_struct *task,
>>          * TS_COMPAT is set for 32-bit syscall entries and then
>>          * remains set until we return to user mode.
>>          */
>> -       if (task_thread_info(task)->status & TS_COMPAT)
>> +       if (task->thread.status & TS_COMPAT)
>>                 /*
>>                  * Sign-extend the value so (int)-EFOO becomes (long)-EFOO
>>                  * and will match correctly in comparisons.
>> @@ -116,7 +116,7 @@ static inline void syscall_get_arguments(struct task_struct *task,
>>                                          unsigned long *args)
>>  {
>>  # ifdef CONFIG_IA32_EMULATION
>> -       if (task_thread_info(task)->status & TS_COMPAT)
>> +       if (task->thread.status & TS_COMPAT)
>>                 switch (i) {
>>                 case 0:
>>                         if (!n--) break;
>> @@ -177,7 +177,7 @@ static inline void syscall_set_arguments(struct task_struct *task,
>>                                          const unsigned long *args)
>>  {
>>  # ifdef CONFIG_IA32_EMULATION
>> -       if (task_thread_info(task)->status & TS_COMPAT)
>> +       if (task->thread.status & TS_COMPAT)
>>                 switch (i) {
>>                 case 0:
>>                         if (!n--) break;
>> @@ -234,21 +234,8 @@ static inline void syscall_set_arguments(struct task_struct *task,
>>
>>  static inline int syscall_get_arch(void)
>>  {
>> -#ifdef CONFIG_IA32_EMULATION
>> -       /*
>> -        * TS_COMPAT is set for 32-bit syscall entry and then
>> -        * remains set until we return to user mode.
>> -        *
>> -        * TIF_IA32 tasks should always have TS_COMPAT set at
>> -        * system call time.
>> -        *
>> -        * x32 tasks should be considered AUDIT_ARCH_X86_64.
>> -        */
>> -       if (task_thread_info(current)->status & TS_COMPAT)
>> -               return AUDIT_ARCH_I386;
>> -#endif
>> -       /* Both x32 and x86_64 are considered "64-bit". */
>> -       return AUDIT_ARCH_X86_64;
>> +       /* x32 tasks should be considered AUDIT_ARCH_X86_64. */
>> +       return in_ia32_syscall() ? AUDIT_ARCH_I386 : AUDIT_ARCH_X86_64;
>>  }
>>  #endif /* CONFIG_X86_32 */
>>
>> diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
>> index b45ffdda3549..7b42c1e462ac 100644
>> --- a/arch/x86/include/asm/thread_info.h
>> +++ b/arch/x86/include/asm/thread_info.h
>> @@ -55,7 +55,6 @@ struct task_struct;
>>  struct thread_info {
>>         struct task_struct      *task;          /* main task structure */
>>         __u32                   flags;          /* low level flags */
>> -       __u32                   status;         /* thread synchronous flags */
>>         __u32                   cpu;            /* current CPU */
>>  };
>>
>> @@ -211,28 +210,14 @@ static inline unsigned long current_stack_pointer(void)
>>
>>  #endif
>>
>> -/*
>> - * Thread-synchronous status.
>> - *
>> - * This is different from the flags in that nobody else
>> - * ever touches our thread-synchronous status, so we don't
>> - * have to worry about atomic accesses.
>> - */
>> -#define TS_COMPAT              0x0002  /* 32bit syscall active (64BIT)*/
>> -
>>  #ifndef __ASSEMBLY__
>>
>> -static inline bool in_ia32_syscall(void)
>> -{
>>  #ifdef CONFIG_X86_32
>> -       return true;
>> -#endif
>> -#ifdef CONFIG_IA32_EMULATION
>> -       if (current_thread_info()->status & TS_COMPAT)
>> -               return true;
>> +#define in_ia32_syscall() true
>> +#else
>> +#define in_ia32_syscall() (IS_ENABLED(CONFIG_IA32_EMULATION) && \
>> +                          current->thread.status & TS_COMPAT)
>>  #endif
>> -       return false;
>> -}
>>
>>  /*
>>   * Force syscall return via IRET by making it look as if there was
>> diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
>> index 2bd5c6ff7ee7..a91a6ead24a2 100644
>> --- a/arch/x86/kernel/asm-offsets.c
>> +++ b/arch/x86/kernel/asm-offsets.c
>> @@ -30,7 +30,6 @@
>>  void common(void) {
>>         BLANK();
>>         OFFSET(TI_flags, thread_info, flags);
>> -       OFFSET(TI_status, thread_info, status);
>
> TI_status can be deleted.  It's last users were removed in commit ee08c6bd.

Indeed.

Just to double-check: are you saying that this patch is okay?

--Andy

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