linux-kernel - Re: [PATCH v7 28/41] x86: Introduce userspace API for shadow stack

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Message-ID: <f020ce5ba5727dc6e25b6cc158be15e9c2ad0bee.camel@intel.com>
Date:   Fri, 10 Mar 2023 20:27:11 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
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Subject: Re: [PATCH v7 28/41] x86: Introduce userspace API for shadow stack

On Fri, 2023-03-10 at 12:00 -0800, H.J. Lu wrote:
> > > So it does:
> > > 1. Enable shadow stack
> > > 2. Call elf libs checking functions
> > > 3. If all good, lock shadow stack. Else, disable shadow stack.
> > > 4. Return from elf checking functions and if shstk is enabled,
> > > don't
> > > underflow because it was enabled in step 1 and we have return
> > > addresses
> > > from 2 on the shadow stack
> > > 
> > > I'm wondering if this can't be improved in glibc to look like:
> > > 1. Check elf libs, and record it somewhere
> > > 2. Wait until just the right spot
> > > 3. If all good, enable and lock shadow stack.
> > 
> > I will try it out.
> > 
> 
> Currently glibc enables shadow stack as early as possible.  There
> are only a few places where a function call in glibc never returns.
> We can enable shadow stack just before calling main.   There are
> quite some code paths without shadow stack protection.   Is this
> an issue?

Thanks for checking. Hmm, does the loader get attacked?