Date: Fri, 8 Feb 2019 15:26:43 +0100 From: Peter Zijlstra <peterz@...radead.org> To: "Reshetova, Elena" <elena.reshetova@...el.com> Cc: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, "luto@...nel.org" <luto@...nel.org>, "tglx@...utronix.de" <tglx@...utronix.de>, "mingo@...hat.com" <mingo@...hat.com>, "bp@...en8.de" <bp@...en8.de>, "keescook@...omium.org" <keescook@...omium.org>, "tytso@....edu" <tytso@....edu> 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 unaffected.
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