On Fri, Aug 07, 2020 at 03:14:29PM +0200, Greg KH wrote: > On Thu, Aug 06, 2020 at 01:00:54PM -0700, Florian Fainelli wrote: > > > > > > On 7/20/2020 11:26 AM, Florian Fainelli wrote: > > > On 7/20/20 6:04 AM, Greg KH wrote: > > >> On Thu, Jul 09, 2020 at 12:50:23PM -0700, Florian Fainelli wrote: > > >>> From: Will Deacon <will.deacon@xxxxxxx> > > >>> > > >>> commit 679db70801da9fda91d26caf13bf5b5ccc74e8e8 upstream > > >>> > > >>> Some CPUs can speculate past an ERET instruction and potentially perform > > >>> speculative accesses to memory before processing the exception return. > > >>> Since the register state is often controlled by a lower privilege level > > >>> at the point of an ERET, this could potentially be used as part of a > > >>> side-channel attack. > > >>> > > >>> This patch emits an SB sequence after each ERET so that speculation is > > >>> held up on exception return. > > >>> > > >>> Signed-off-by: Will Deacon <will.deacon@xxxxxxx> > > >>> [florian: Adjust hyp-entry.S to account for the label > > >>> added change to hyp/entry.S] > > >>> Signed-off-by: Florian Fainelli <f.fainelli@xxxxxxxxx> > > >>> --- > > >>> Changes in v2: > > >>> > > >>> - added missing hunk in hyp/entry.S per Will's feedback > > >> > > >> What about 4.19.y and 4.14.y trees? I can't take something for 4.9.y > > >> and then have a regression if someone moves to a newer release, right? > > > > > > Sure, send you candidates for 4.14 and 4.19. > > > > Greg, did you have a chance to queue those changes for 4.9, 4.14 and 4.19? > > > > https://lore.kernel.org/linux-arm-kernel/20200720182538.13304-1-f.fainelli@xxxxxxxxx/ > > https://lore.kernel.org/linux-arm-kernel/20200720182937.14099-1-f.fainelli@xxxxxxxxx/ > > https://lore.kernel.org/linux-arm-kernel/20200709195034.15185-1-f.fainelli@xxxxxxxxx/ > > Nope, I was waiting for Will's "ack" for these. This patch doesn't even build for me (the 'sb' macro is not defined in 4.9), and I really wonder why we bother backporting it at all. Nobody's ever shown it to be a problem in practice, and it's clear that this is just being submitted to tick a box rather than anything else (otherwise it would build, right?). So I'm not going to Ack any of them. As with a lot of this side-channel stuff the cure is far worse than the disease. Will
