linux-kernel - Re: [PATCH v6 1/7] mseal, system mappings: kernel config and header change

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Message-ID: <202502241053.1FF33D5B0@keescook>
Date: Mon, 24 Feb 2025 10:55:26 -0800
From: Kees Cook <kees@...nel.org>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Jeff Xu <jeffxu@...omium.org>, akpm@...ux-foundation.org,
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Subject: Re: [PATCH v6 1/7] mseal, system mappings: kernel config and header
 change

On Mon, Feb 24, 2025 at 10:52:13AM -0800, Dave Hansen wrote:
> On 2/24/25 10:44, Jeff Xu wrote:
> > For example:
> > Consider the case below in src/third_party/kernel/v6.6/fs/proc/task_mmu.c,
> > 
> > #ifdef CONFIG_64BIT
> > [ilog2(VM_SEALED)] = "sl",
> > #endif
> > 
> > Redefining VM_SEALED  to VM_NONE for 32 bit won't detect the problem
> > in case that  "#ifdef CONFIG_64BIT" line is missing.
> > 
> > Please note, this has been like this since the first version of
> > mseal() RFC patch, and I prefer to keep it this way.
> 
> That logic is reasonable. But it's different from the _vast_ majority of
> other flags.
> 
> So what justifies VM_SEALED being so different? It's leading to pretty
> objectively ugly code in this series.

Note that VM_SEALED is the "is this VMA sealed?" bit itself. The define
for "should we perform system mapping sealing?" is intentionally separate
here, so that it can be Kconfig and per-arch toggled, etc.

As for the name, I have no strong opinion. Perhaps VM_SEALED_SYSTEM_MAPPING ?

-Kees

-- 
Kees Cook