Re: [PATCH stable v4.9 v2] arm64: entry: Place an SB sequence following an ERET instruction

[Greg KH]

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?

thanks,

greg k-h