Re: [PATCH 15/19] x86, mpx: do 32-bit-only cmpxchg for 32-bit apps

Thomas Gleixner
2015-05-18T21:21:57Z

On Fri, 8 May 2015, Dave Hansen wrote:
> +static int mpx_cmpxchg_bd_entry(struct mm_struct *mm,
> + unsigned long *actual_old_val_ptr, long __user *bd_entry_addr,
> + unsigned long expected_old_val, unsigned long new_bd_entry)

I know that you tried to use descriptive argument names, but the
result is close to camel case argument lists :)

Also why is *bd_entry_addr a long? Shouldn't that be unsigned long?

static int mpx_cmpxchg_bd_entry(struct mm_struct *mm,
unsigned long __user *addr,
unsigned long oldval, unsigned long newval,
unsigned long *curval)

or something like that should be sufficient, methinks.

> +{
> + int ret;
> + /*
> + * user_atomic_cmpxchg_inatomic() actually uses sizeof()
> + * the pointer that we pass to it to figure out how much
> + * data to cmpxchg. We have to be careful here not to
> + * pass a pointer to a 64-bit data type when we only want
> + * a 32-bit copy.
> + */
> + if (is_64bit_mm(mm)) {
> + ret = user_atomic_cmpxchg_inatomic(actual_old_val_ptr,
> + bd_entry_addr, expected_old_val, new_bd_entry);
> + } else {
> + u32 uninitialized_var(actual_old_val_32);
> + u32 expected_old_val_32 = expected_old_val;
> + u32 new_bd_entry_32 = new_bd_entry;
> + u32 __user *bd_entry_32 = (u32 __user *)bd_entry_addr;

Newline between variables and code please.

> + ret = user_atomic_cmpxchg_inatomic(&actual_old_val_32,
> + bd_entry_32, expected_old_val_32,
> + new_bd_entry_32);
> + if (!ret)
> + *actual_old_val_ptr = actual_old_val_32;

You can update that unconditionally.

Thanks,

tglx