RE: [PATCH v2 for-4.14] x86/livepatch: Make livepatching compatible with CET Shadow Stacks

[Paul Durrant <xadimgnik@xxxxxxxxx>]

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: 26 June 2020 14:15
> To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>; Wei Liu <wl@xxxxxxx>; Roger 
> Pau Monné
> <roger.pau@xxxxxxxxxx>; Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>; Ross 
> Lagerwall
> <ross.lagerwall@xxxxxxxxxx>; Pawel Wieczorkiewicz <wipawel@xxxxxxxxx>; Paul 
> Durrant <paul@xxxxxxx>
> Subject: Re: [PATCH v2 for-4.14] x86/livepatch: Make livepatching compatible 
> with CET Shadow Stacks
> 
> On 26.06.2020 14:24, Andrew Cooper wrote:
> > Just like the alternatives infrastructure, the livepatch infrastructure
> > disables CR0.WP to perform patching, which is not permitted with CET active.
> >
> > Modify arch_livepatch_{quiesce,revive}() to disable CET before disabling WP,
> > and reset the dirty bits on all virtual regions before re-enabling CET.
> >
> > One complication is that arch_livepatch_revive() has to fix up the top of 
> > the
> > shadow stack.  This depends on the functions not being inlined, even under
> > LTO.  Another limitation is that reset_virtual_region_perms() may shatter 
> > the
> > final superpage of .text depending on alignment.
> >
> > This logic, and its downsides, are temporary until the patching 
> > infrastructure
> > can be adjusted to not use CR0.WP.
> 
> In particular on this basis ...
> 
> > Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> 
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Release-acked-by: Paul Durrant <paul@xxxxxxx>

> 
> Jan