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
>
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