static int mpx_cmpxchg_bd_entry(struct mm_struct *mm,
unsigned long *curval,
unsigned long __user *addr,
unsigned long old_val, unsigned long new_val)
{
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(curval,
addr, old_val, new_val);
} else {
u32 uninitialized_var(curval_32);
u32 old_val_32 = old_val;
u32 new_val_32 = new_val;
u32 __user *addr_32 = (u32 __user *)addr;
ret = user_atomic_cmpxchg_inatomic(&curval_32,
addr_32, old_val_32, new_val_32);
*curval = curval_32;
}
return ret;
}
static int unmap_single_bt(struct mm_struct *mm,
long __user *bd_entry, unsigned long bt_addr)
{
unsigned long expected_old_val = bt_addr | MPX_BD_ENTRY_VALID_FLAG;
unsigned long actual_old_val = 0;
int ret;
while (1) {
int need_write = 1;
pagefault_disable();
ret = user_atomic_cmpxchg_inatomic(&actual_old_val, bd_entry,
expected_old_val, 0);
pagefault_enable();
if (!ret)
break;
if (ret == -EFAULT)
ret = mpx_resolve_fault(bd_entry, need_write);
/*
* If we could not resolve the fault, consider it
* userspace's fault and error out.
*/
if (ret)
return ret;
}
/*
* The cmpxchg was performed, check the results.
*/
if (actual_old_val != expected_old_val) {
/*
* Someone else raced with us to unmap the table.
* There was no bounds table pointed to by the
* directory, so declare success. Somebody freed
* it.
*/
if (!actual_old_val)
return 0;
/*
* Something messed with the bounds directory
* entry. We hold mmap_sem for read or write
* here, so it could not be a _new_ bounds table
* that someone just allocated. Something is
* wrong, so pass up the error and SIGSEGV.
*/
return -EINVAL;
}
/*
* Note, we are likely being called under do_munmap() already. To
* avoid recursion, do_munmap() will check whether it comes
* from one bounds table through VM_MPX flag.
*/
return do_munmap(mm, bt_addr, MPX_BT_SIZE_BYTES);
}
/*
* With 32-bit mode, MPX_BT_SIZE_BYTES is 4MB, and the size of each
* bounds table is 16KB. With 64-bit mode, MPX_BT_SIZE_BYTES is 2GB,
* and the size of each bounds table is 4MB.
*/
static int allocate_bt(long __user *bd_entry)
{
unsigned long expected_old_val = 0;
unsigned long actual_old_val = 0;
unsigned long bt_addr;
int ret = 0;
/*
* Carve the virtual space out of userspace for the new
* bounds table:
*/
bt_addr = mpx_mmap(MPX_BT_SIZE_BYTES);
if (IS_ERR((void *)bt_addr))
return PTR_ERR((void *)bt_addr);
/*
* Set the valid flag (kinda like _PAGE_PRESENT in a pte)
*/
bt_addr = bt_addr | MPX_BD_ENTRY_VALID_FLAG;
/*
* Go poke the address of the new bounds table in to the
* bounds directory entry out in userspace memory. Note:
* we may race with another CPU instantiating the same table.
* In that case the cmpxchg will see an unexpected
* 'actual_old_val'.
*
* This can fault, but that's OK because we do not hold
* mmap_sem at this point, unlike some of the other part
* of the MPX code that have to pagefault_disable().
*/
ret = user_atomic_cmpxchg_inatomic(&actual_old_val, bd_entry,
expected_old_val, bt_addr);
if (ret)
goto out_unmap;
/*
* The user_atomic_cmpxchg_inatomic() will only return nonzero
* for faults, *not* if the cmpxchg itself fails. Now we must
* verify that the cmpxchg itself completed successfully.
*/
/*
* We expected an empty 'expected_old_val', but instead found
* an apparently valid entry. Assume we raced with another
* thread to instantiate this table and desclare succecss.
*/
if (actual_old_val & MPX_BD_ENTRY_VALID_FLAG) {
ret = 0;
goto out_unmap;
}
/*
* We found a non-empty bd_entry but it did not have the
* VALID_FLAG set. Return an error which will result in
* a SEGV since this probably means that somebody scribbled
* some invalid data in to a bounds table.
*/
if (expected_old_val != actual_old_val) {
ret = -EINVAL;
goto out_unmap;
}
return 0;
out_unmap:
vm_munmap(bt_addr & MPX_BT_ADDR_MASK, MPX_BT_SIZE_BYTES);
return ret;
}
