linux-kernel - Re: [PATCH v7 38/41] x86/fpu: Add helper for initing features

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Message-ID: <20230313171031.GEZA9ZB01FRjCo98pr@fat_crate.local>
Date:   Mon, 13 Mar 2023 18:10:31 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
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Subject: Re: [PATCH v7 38/41] x86/fpu: Add helper for initing features

On Mon, Mar 13, 2023 at 04:10:14PM +0000, Edgecombe, Rick P wrote:
> This seems more clear. I'm sorry for the noise here though, because
> this has made me realize that the initing logic should never be hit. We
> used to support the full CET_U state in ptrace, but then dropped it to
> just the SSP and only allowed it when shadow stack is active.

Right, you do check that at function entry.

> This means that CET_U will always have at least the CET_SHSTK_EN bit
> set and so not be in the init state. So this can probably just warn
> and bail if it sees an init state.

I don't mind the additional checks as this is a security thing so
sanity checks are good, especially if they're cheap.

And you don't need to reinit the buffer - just scream loudly when get_xsave_addr()
returns NULL.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette