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Message-ID: <202212021840.D890531@keescook>
Date: Fri, 2 Dec 2022 18:40:02 -0800
From: Kees Cook <keescook@...omium.org>
To: Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc: x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
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Subject: Re: [PATCH v4 24/39] mm: Warn on shadow stack memory in wrong vma
On Fri, Dec 02, 2022 at 04:35:51PM -0800, Rick Edgecombe wrote:
> The x86 Control-flow Enforcement Technology (CET) feature includes a new
> type of memory called shadow stack. This shadow stack memory has some
> unusual properties, which requires some core mm changes to function
> properly.
>
> One sharp edge is that PTEs that are both Write=0 and Dirty=1 are
> treated as shadow by the CPU, but this combination used to be created by
> the kernel on x86. Previous patches have changed the kernel to now avoid
> creating these PTEs unless they are for shadow stack memory. In case any
> missed corners of the kernel are still creating PTEs like this for
> non-shadow stack memory, and to catch any re-introductions of the logic,
> warn if any shadow stack PTEs (Write=0, Dirty=1) are found in non-shadow
> stack VMAs when they are being zapped. This won't catch transient cases
> but should have decent coverage. It will be compiled out when shadow
> stack is not configured.
>
> In order to check if a pte is shadow stack in core mm code, add default
> implmentations for pte_shstk() and pmd_shstk().
>
> Tested-by: Pengfei Xu <pengfei.xu@...el.com>
> Tested-by: John Allen <john.allen@....com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
--
Kees Cook
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