Re: [PATCH -next v5 2/3] x86/mce: set MCE_IN_KERNEL_COPYIN for DEFAULT_MCE_SAFE exception

[Tong Tiangen]

在 2024/3/28 6:05, Borislav Petkov 写道:
> On Sun, Feb 18, 2024 at 06:08:14PM +0800, Tong Tiangen wrote:
> > 1. The copy_mc_to_kernel() is used in the coredump, KSM, and COW
> > scenarios, in these scenarios, the src mem stores the user data and the
> > kernel use kernel address to access the src mem(using kmap()).
> >
> > 2. the src mem of copy_mc_to_user() is currently only used by the DAX:
>
> You mean just because it currently is used somewhere which probably is
> ok - no clue what DAX does - and even if the source address is still
> *kernel* memory and even at the danger that someone else might use it in
> the future and think the handling on a potential #MC is ok, you're still
> arguing that this is the right thing to do perhaps because it fits your
> use case?!
>
> Sorry Tiangen, not gonna happen.

I left the office last week and felt sorry for the lateness of the
reply.

You are right. Our current processing is based on "experience" rather
than interface constraints.

is_copy_from_user() determines whether a user is a "copy user" based on
fault_in_kernel_space(). Therefore, it returns false for
copy_mc_to_kernel()/copy_mc_to_user(). As a result, MCE_IN_KERNEL_COPYIN
cannot be set in error_context().

Comprehensive consideration of all factors, it is better to manually
call memory_failure_queue() to handle this problem case by case.

Finally, do we consider accepting only the patch 1/3 ?

Thanks,
Tong.