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Date: Fri, 8 Feb 2019 15:26:43 +0100
From: Peter Zijlstra <>
To: "Reshetova, Elena" <>
Cc: "" <>,
	"" <>,
	"" <>,
	"" <>,
	"" <>,
	"" <>,
	"" <>
Subject: Re: [RFC PATCH] x86/entry/64: randomize kernel stack offset upon
 system call

On Fri, Feb 08, 2019 at 01:20:09PM +0000, Reshetova, Elena wrote:
> > On Fri, Feb 08, 2019 at 02:15:49PM +0200, Elena Reshetova wrote:

> > 
> > Why can't we change the stack offset periodically from an interrupt or
> > so, and then have every later entry use that.
> Hm... This sounds more complex conceptually - we cannot touch
> stack when it is in use, so we have to periodically probe for a 
> good time (when process is in userspace I guess) to change it from an interrupt?
> IMO trampoline stack provides such a good clean place for doing it and we
> have stackleak there doing stack cleanup, so would make sense to keep
> these features operating together.

The idea was to just change a per-cpu (possible per-task if you ctxsw
it) offset that is used on entry to offset the stack.

So only entries after the change will have the updated offset, any
in-progress syscalls will continue with their current offset and will be

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