[PATCH v2] arm64: fix current_thread_info()->addr_limit setup

[PATCH v2] arm64: fix current_thread_info()->addr_limit setup

[Yury Norov]

At elf loading in flush_old_exec() in fs/exec.c, generic code sets
current_thread_info()->addr_limit to one that corresponds aarch64 value,
and ignores compat mode there as corresponding status setup happens
later on in load_elf_binary() by SET_PERSONALITY() macro. As result,
compat task has wrong addr_limit, and it may cause various bugs.

This patch fixes it. It also fixes USER_DS macro to return different
values depending on compat at runtime.

It was discovered during ilp32 development. See details here:
https://lkml.org/lkml/2016/5/11/975

v2:
 flush tpidrro_el0 unconditionally in tls_thread_flush() as if exec() is
 called by aarch64 task, is_compat_task() fails even if new thread is
 aarch32.

Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>
---
 arch/arm64/include/asm/elf.h     | 11 +++++++++--
 arch/arm64/include/asm/uaccess.h |  2 +-
 arch/arm64/kernel/process.c      | 18 +++++++-----------
 3 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 24ed037..fda75ce 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -138,7 +138,10 @@ typedef struct user_fpsimd_state elf_fpregset_t;
  */
 #define ELF_PLAT_INIT(_r, load_addr)	(_r)->regs[0] = 0
 
-#define SET_PERSONALITY(ex)		clear_thread_flag(TIF_32BIT);
+#define SET_PERSONALITY(ex) do {					\
+	clear_thread_flag(TIF_32BIT);					\
+	set_fs(TASK_SIZE_64);						\
+} while (0)
 
 #define ARCH_DLINFO							\
 do {									\
@@ -181,7 +184,11 @@ typedef compat_elf_greg_t		compat_elf_gregset_t[COMPAT_ELF_NGREG];
 					 ((x)->e_flags & EF_ARM_EABI_MASK))
 
 #define compat_start_thread		compat_start_thread
-#define COMPAT_SET_PERSONALITY(ex)	set_thread_flag(TIF_32BIT);
+#define COMPAT_SET_PERSONALITY(ex) do {					\
+	set_thread_flag(TIF_32BIT);					\
+	set_fs(TASK_SIZE_32);						\
+} while (0)
+
 #define COMPAT_ARCH_DLINFO
 extern int aarch32_setup_vectors_page(struct linux_binprm *bprm,
 				      int uses_interp);
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 0685d74..5b269e6 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -60,7 +60,7 @@ extern int fixup_exception(struct pt_regs *regs);
 #define KERNEL_DS	(-1UL)
 #define get_ds()	(KERNEL_DS)
 
-#define USER_DS		TASK_SIZE_64
+#define USER_DS		TASK_SIZE
 #define get_fs()	(current_thread_info()->addr_limit)
 
 static inline void set_fs(mm_segment_t fs)
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 8062482..2b25930 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -211,17 +211,13 @@ static void tls_thread_flush(void)
 {
 	asm ("msr tpidr_el0, xzr");
 
-	if (is_compat_task()) {
-		current->thread.tp_value = 0;
-
-		/*
-		 * We need to ensure ordering between the shadow state and the
-		 * hardware state, so that we don't corrupt the hardware state
-		 * with a stale shadow state during context switch.
-		 */
-		barrier();
-		asm ("msr tpidrro_el0, xzr");
-	}
+	/*
+	 * We need to ensure ordering between the shadow state and the
+	 * hardware state, so that we don't corrupt the hardware state
+	 * with a stale shadow state during context switch.
+	 */
+	barrier();
+	asm ("msr tpidrro_el0, xzr");
 }
 
 void flush_thread(void)
-- 
2.5.0

Re: [PATCH v2] arm64: fix current_thread_info()->addr_limit setup

[Catalin Marinas]

On Thu, May 12, 2016 at 07:06:03PM +0300, Yury Norov wrote:
> diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
> index 24ed037..fda75ce 100644
> --- a/arch/arm64/include/asm/elf.h
> +++ b/arch/arm64/include/asm/elf.h
> @@ -138,7 +138,10 @@ typedef struct user_fpsimd_state elf_fpregset_t;
>   */
>  #define ELF_PLAT_INIT(_r, load_addr)	(_r)->regs[0] = 0
>  
> -#define SET_PERSONALITY(ex)		clear_thread_flag(TIF_32BIT);
> +#define SET_PERSONALITY(ex) do {					\
> +	clear_thread_flag(TIF_32BIT);					\
> +	set_fs(TASK_SIZE_64);						\
> +} while (0)
>  
>  #define ARCH_DLINFO							\
>  do {									\
> @@ -181,7 +184,11 @@ typedef compat_elf_greg_t		compat_elf_gregset_t[COMPAT_ELF_NGREG];
>  					 ((x)->e_flags & EF_ARM_EABI_MASK))
>  
>  #define compat_start_thread		compat_start_thread
> -#define COMPAT_SET_PERSONALITY(ex)	set_thread_flag(TIF_32BIT);
> +#define COMPAT_SET_PERSONALITY(ex) do {					\
> +	set_thread_flag(TIF_32BIT);					\
> +	set_fs(TASK_SIZE_32);						\
> +} while (0)
> +
>  #define COMPAT_ARCH_DLINFO
>  extern int aarch32_setup_vectors_page(struct linux_binprm *bprm,
>  				      int uses_interp);
> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> index 0685d74..5b269e6 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -60,7 +60,7 @@ extern int fixup_exception(struct pt_regs *regs);
>  #define KERNEL_DS	(-1UL)
>  #define get_ds()	(KERNEL_DS)
>  
> -#define USER_DS		TASK_SIZE_64
> +#define USER_DS		TASK_SIZE

We can avoid the USER_DS change as long as SET_PERSONALITY updates the
thread's addr_limit. There are very few explicit set_fs(USER_DS) calls
and they are on the thread exit path (or exec).

That's unless we try to make a generic set_fs(USER_DS) addition to
something like setup_new_exec() and we wouldn't need the SET_PERSONALITY
changes:

diff --git a/fs/exec.c b/fs/exec.c
index c4010b8207a1..54cc537f5986 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1226,6 +1226,9 @@ EXPORT_SYMBOL(would_dump);
 
 void setup_new_exec(struct linux_binprm * bprm)
 {
+	/* set the address limit for the new executable */
+	set_fs(USER_DS);
+
 	arch_pick_mmap_layout(current->mm);
 
 	/* This is the point of no return */

>  #define get_fs()	(current_thread_info()->addr_limit)
>  
>  static inline void set_fs(mm_segment_t fs)
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index 8062482..2b25930 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -211,17 +211,13 @@ static void tls_thread_flush(void)
>  {
>  	asm ("msr tpidr_el0, xzr");
>  
> -	if (is_compat_task()) {
> -		current->thread.tp_value = 0;
> -
> -		/*
> -		 * We need to ensure ordering between the shadow state and the
> -		 * hardware state, so that we don't corrupt the hardware state
> -		 * with a stale shadow state during context switch.
> -		 */
> -		barrier();
> -		asm ("msr tpidrro_el0, xzr");
> -	}
> +	/*
> +	 * We need to ensure ordering between the shadow state and the
> +	 * hardware state, so that we don't corrupt the hardware state
> +	 * with a stale shadow state during context switch.
> +	 */
> +	barrier();
> +	asm ("msr tpidrro_el0, xzr");
>  }

Why did you dropped tp_value initialisation? Context switching on native
64-bit tasks rely on copying the tpidr_el0 in and out of tp_value.
However, compat tasks use the read-only tpidrro_el0 register set
explicitly via a system call. Until this call happens, the TLS register
would contain some garbage after the thread has been switched back in.

-- 
Catalin

Re: [PATCH v2] arm64: fix current_thread_info()->addr_limit setup

[Yury Norov]

On Thu, May 12, 2016 at 06:22:03PM +0100, Catalin Marinas wrote:
> On Thu, May 12, 2016 at 07:06:03PM +0300, Yury Norov wrote:
> > diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
> > index 24ed037..fda75ce 100644
> > --- a/arch/arm64/include/asm/elf.h
> > +++ b/arch/arm64/include/asm/elf.h
> > @@ -138,7 +138,10 @@ typedef struct user_fpsimd_state elf_fpregset_t;
> >   */
> >  #define ELF_PLAT_INIT(_r, load_addr)	(_r)->regs[0] = 0
> >  
> > -#define SET_PERSONALITY(ex)		clear_thread_flag(TIF_32BIT);
> > +#define SET_PERSONALITY(ex) do {					\
> > +	clear_thread_flag(TIF_32BIT);					\
> > +	set_fs(TASK_SIZE_64);						\
> > +} while (0)
> >  
> >  #define ARCH_DLINFO							\
> >  do {									\
> > @@ -181,7 +184,11 @@ typedef compat_elf_greg_t		compat_elf_gregset_t[COMPAT_ELF_NGREG];
> >  					 ((x)->e_flags & EF_ARM_EABI_MASK))
> >  
> >  #define compat_start_thread		compat_start_thread
> > -#define COMPAT_SET_PERSONALITY(ex)	set_thread_flag(TIF_32BIT);
> > +#define COMPAT_SET_PERSONALITY(ex) do {					\
> > +	set_thread_flag(TIF_32BIT);					\
> > +	set_fs(TASK_SIZE_32);						\
> > +} while (0)
> > +
> >  #define COMPAT_ARCH_DLINFO
> >  extern int aarch32_setup_vectors_page(struct linux_binprm *bprm,
> >  				      int uses_interp);
> > diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> > index 0685d74..5b269e6 100644
> > --- a/arch/arm64/include/asm/uaccess.h
> > +++ b/arch/arm64/include/asm/uaccess.h
> > @@ -60,7 +60,7 @@ extern int fixup_exception(struct pt_regs *regs);
> >  #define KERNEL_DS	(-1UL)
> >  #define get_ds()	(KERNEL_DS)
> >  
> > -#define USER_DS		TASK_SIZE_64
> > +#define USER_DS		TASK_SIZE
> 
> We can avoid the USER_DS change as long as SET_PERSONALITY updates the
> thread's addr_limit. There are very few explicit set_fs(USER_DS) calls
> and they are on the thread exit path (or exec).
> 
> That's unless we try to make a generic set_fs(USER_DS) addition to
> something like setup_new_exec() and we wouldn't need the SET_PERSONALITY
> changes:
> 

I think we'd better leave it fixed. Just because it's correct. Now it
looks like we have fixed early usages (before SET_PERSONALITY()) of
set_fs() explicitly, and normal usages (and possible in future) by
fixing USER_DS.

> diff --git a/fs/exec.c b/fs/exec.c
> index c4010b8207a1..54cc537f5986 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1226,6 +1226,9 @@ EXPORT_SYMBOL(would_dump);
>  
>  void setup_new_exec(struct linux_binprm * bprm)
>  {
> +	/* set the address limit for the new executable */
> +	set_fs(USER_DS);
> +
>  	arch_pick_mmap_layout(current->mm);
>  
>  	/* This is the point of no return */
> 
> >  #define get_fs()	(current_thread_info()->addr_limit)
> >  
> >  static inline void set_fs(mm_segment_t fs)
> > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> > index 8062482..2b25930 100644
> > --- a/arch/arm64/kernel/process.c
> > +++ b/arch/arm64/kernel/process.c
> > @@ -211,17 +211,13 @@ static void tls_thread_flush(void)
> >  {
> >  	asm ("msr tpidr_el0, xzr");
> >  
> > -	if (is_compat_task()) {
> > -		current->thread.tp_value = 0;
> > -
> > -		/*
> > -		 * We need to ensure ordering between the shadow state and the
> > -		 * hardware state, so that we don't corrupt the hardware state
> > -		 * with a stale shadow state during context switch.
> > -		 */
> > -		barrier();
> > -		asm ("msr tpidrro_el0, xzr");
> > -	}
> > +	/*
> > +	 * We need to ensure ordering between the shadow state and the
> > +	 * hardware state, so that we don't corrupt the hardware state
> > +	 * with a stale shadow state during context switch.
> > +	 */
> > +	barrier();
> > +	asm ("msr tpidrro_el0, xzr");
> >  }
> 
> Why did you dropped tp_value initialisation? Context switching on native
> 64-bit tasks rely on copying the tpidr_el0 in and out of tp_value.
> However, compat tasks use the read-only tpidrro_el0 register set
> explicitly via a system call. Until this call happens, the TLS register
> would contain some garbage after the thread has been switched back in.
> 

OOPS, my fault. I just missed a line. Should I send v3, or you or Arnd
can apply it and fix in your branch?

> -- 
> Catalin
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Re: [PATCH v2] arm64: fix current_thread_info()->addr_limit setup

[Catalin Marinas]

On Thu, May 12, 2016 at 09:03:42PM +0300, Yury Norov wrote:
> On Thu, May 12, 2016 at 06:22:03PM +0100, Catalin Marinas wrote:
> > On Thu, May 12, 2016 at 07:06:03PM +0300, Yury Norov wrote:
> > > diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
> > > index 24ed037..fda75ce 100644
> > > --- a/arch/arm64/include/asm/elf.h
> > > +++ b/arch/arm64/include/asm/elf.h
> > > @@ -138,7 +138,10 @@ typedef struct user_fpsimd_state elf_fpregset_t;
> > >   */
> > >  #define ELF_PLAT_INIT(_r, load_addr)	(_r)->regs[0] = 0
> > >  
> > > -#define SET_PERSONALITY(ex)		clear_thread_flag(TIF_32BIT);
> > > +#define SET_PERSONALITY(ex) do {					\
> > > +	clear_thread_flag(TIF_32BIT);					\
> > > +	set_fs(TASK_SIZE_64);						\
> > > +} while (0)
> > >  
> > >  #define ARCH_DLINFO							\
> > >  do {									\
> > > @@ -181,7 +184,11 @@ typedef compat_elf_greg_t		compat_elf_gregset_t[COMPAT_ELF_NGREG];
> > >  					 ((x)->e_flags & EF_ARM_EABI_MASK))
> > >  
> > >  #define compat_start_thread		compat_start_thread
> > > -#define COMPAT_SET_PERSONALITY(ex)	set_thread_flag(TIF_32BIT);
> > > +#define COMPAT_SET_PERSONALITY(ex) do {					\
> > > +	set_thread_flag(TIF_32BIT);					\
> > > +	set_fs(TASK_SIZE_32);						\
> > > +} while (0)
> > > +
> > >  #define COMPAT_ARCH_DLINFO
> > >  extern int aarch32_setup_vectors_page(struct linux_binprm *bprm,
> > >  				      int uses_interp);
> > > diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> > > index 0685d74..5b269e6 100644
> > > --- a/arch/arm64/include/asm/uaccess.h
> > > +++ b/arch/arm64/include/asm/uaccess.h
> > > @@ -60,7 +60,7 @@ extern int fixup_exception(struct pt_regs *regs);
> > >  #define KERNEL_DS	(-1UL)
> > >  #define get_ds()	(KERNEL_DS)
> > >  
> > > -#define USER_DS		TASK_SIZE_64
> > > +#define USER_DS		TASK_SIZE
> > 
> > We can avoid the USER_DS change as long as SET_PERSONALITY updates the
> > thread's addr_limit. There are very few explicit set_fs(USER_DS) calls
> > and they are on the thread exit path (or exec).
> > 
> > That's unless we try to make a generic set_fs(USER_DS) addition to
> > something like setup_new_exec() and we wouldn't need the SET_PERSONALITY
> > changes:
> 
> I think we'd better leave it fixed. Just because it's correct. Now it
> looks like we have fixed early usages (before SET_PERSONALITY()) of
> set_fs() explicitly, and normal usages (and possible in future) by
> fixing USER_DS.

Thinking some more, let's first try to change USER_DS to the dynamic
TASK_SIZE and add a generic set_fs(USER_DS) call in setup_new_exec() as
below:

> > diff --git a/fs/exec.c b/fs/exec.c
> > index c4010b8207a1..54cc537f5986 100644
> > --- a/fs/exec.c
> > +++ b/fs/exec.c
> > @@ -1226,6 +1226,9 @@ EXPORT_SYMBOL(would_dump);
> >  
> >  void setup_new_exec(struct linux_binprm * bprm)
> >  {
> > +	/* set the address limit for the new executable */
> > +	set_fs(USER_DS);
> > +
> >  	arch_pick_mmap_layout(current->mm);
> >  
> >  	/* This is the point of no return */
> > 

Cc'ing Al Viro for his opinion here.

In summary: access_ok() behaves differently on native 32-bit kernels vs
64-bit + compat applications because for the latter USER_DS is always
set to the maximum 64-bit TASK_SIZE (x86 and powerpc seem to do
something similar). Changing USER_DS alone in the arch code does not
help since the set_fs(USER_DS) in flush_old_exec() is called prior to
COMPAT_SET_PERSONALITY().

(it's not a serious bug, just some LTP tests failing when they test an
address range going beyond the 4GB limit)

Thanks.

-- 
Catalin