linux-kernel - Re: [PATCH RFC RFT 2/5] fork: Add shadow stack support to clone3()

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Date:   Fri, 27 Oct 2023 17:48:55 +0100
From:   "Szabolcs.Nagy@....com" <Szabolcs.Nagy@....com>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "debug@...osinc.com" <debug@...osinc.com>
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        "keescook@...omium.org" <keescook@...omium.org>,
        "shuah@...nel.org" <shuah@...nel.org>,
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        "fweimer@...hat.com" <fweimer@...hat.com>,
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        "juri.lelli@...hat.com" <juri.lelli@...hat.com>
Subject: Re: [PATCH RFC RFT 2/5] fork: Add shadow stack support to clone3()

The 10/27/2023 15:55, Edgecombe, Rick P wrote:
> Do you have any updated plans to share around your earlier ideas for
> token schemes that try to shoot for more compatibility or security?

not really.

i don't like that shadow stack overflow cannot be handled,
so we have to allocate huge shadow stacks to avoid overflow.

i had ideas how to handle overflow with sigaltstack, but it
is complicated (unwinding, longjmp, swapcontext,..) so
"allocate huge shadow stack" is currently our best design.

the compatibility issues i see:
- dlopen of incompatible lib (multi thread case)
- makecontext shadow stack leaks (userspace api issue)
- huge shadow stack runs into resource limits
- hand crafted stack switching code needs updates
- minor issues around sigaltstack + swapcontext

i don't have an alternate design that makes these go away.
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