RE: [PATCH v4 1/3] x86/mce: Use is_copy_from_user() to determine copy-from-user context

[Luck, Tony]

> The more important part which I asked for already is, is is_copy_from_user()
> exhaustive in determining the that the operation really is a copy from user?
>
> The EX_TYPE_UACCESS things *explicitly* marked such places in the code. Does
> is_copy_from_user() guarantee the same, without false positives?

is_copy_from_user() decodes the instruction that took the trap. It looks for
MOV, MOVZ and MOVS instructions to find the source address, and then
checks whether that's user (< TASK_SIZE_MAX) or kernel.

So no false positives.

There could be some false negatives if some other instruction is doing
the "load" operation.

-Tony