Hi Christoffer,

On 31/01/2019 08:04, Christoffer Dall wrote:

On Thu, Jan 24, 2019 at 04:32:56PM +0000, James Morse wrote:

quoted

The hyp-stub is loaded by the kernel's early startup code at EL2
during boot, before KVM takes ownership later. The hyp-stub's
text is part of the regular kernel text, meaning it can be kprobed.

A breakpoint in the hyp-stub causes the CPU to spin in el2_sync_invalid.

Add it to the __hyp_text.

quoted

This has been a problem since kprobes was merged, it should
probably have been covered in 888b3c8720e0.

I'm not sure __hyp_text is the right place. Its not idmaped,
and as it contains a set of vectors, adding it to the host/hyp
idmap sections could grow them beyond a page... but it does
run with the MMU off, so does need to be cleaned to PoC when
anything wacky, like hibernate happens. With this patch,
hibernate should clean the __hyp_text to PoC too.

How did this code get cleaned before?

It didn't need to be cleaned as KVM executes it with the MMU on.
KVM's MMU-off code lives in the hyp_idmap, which is cleaned. (as is the kernel's
idmap).

The hibernate-cache-cleaning was trying to do the absolute minimum, but the
hyp-stub got forgotten.

Is there a problem you can identify with putting it in __hyp_text?

Seems to me we should just stick it there if it has no negative
side-effects and otherwise we have to make up a separate section with a
specialized meaning.

Yup, there is no problem with the extra cache-maintenance.
The hyp-stub is the odd one out, its runtime code that runs with the MMU off,
but isn't idmaped. I wasn't sure if we wanted to create some special
section.(having to name it is a good enough reason not to!)


Thanks,

James

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