linux-hardening - Re: [PATCH v10 0/5] Introduce mseal

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Date: Tue, 14 May 2024 19:47:46 -0600
From: "Theo de Raadt" <deraadt@...nbsd.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
cc: Matthew Wilcox <willy@...radead.org>,
    Jonathan Corbet <corbet@....net>,
    Andrew Morton <akpm@...ux-foundation.org>, jeffxu@...omium.org,
    keescook@...omium.org, jannh@...gle.com, sroettger@...gle.com,
    gregkh@...uxfoundation.org, usama.anjum@...labora.com,
    Liam.Howlett@...cle.com, surenb@...gle.com, merimus@...gle.com,
    rdunlap@...radead.org, jeffxu@...gle.com, jorgelo@...omium.org,
    groeck@...omium.org, linux-kernel@...r.kernel.org,
    linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
    pedro.falcato@...il.com, dave.hansen@...el.com,
    linux-hardening@...r.kernel.org
Subject: Re: [PATCH v10 0/5] Introduce mseal

Linus Torvalds <torvalds@...ux-foundation.org> wrote:

Regarding mprotect(), POSIX also says:

    An implementation may permit accesses other than those specified by
    prot; however, no implementation shall permit a write to succeed where
    PROT_WRITE has not been set or shall permit any access where PROT_NONE
    alone has been set.

When sealed memory is encountered in the middle of a range, an error
will be returned (which almost noone looks at). Memory after the sealed
region will not be fixed to follow this rule.

It may retain higher permission.

> Maybe some atomicity rules have always been true for BSD, but they've
> never been true for Linux, and while I don't know how authoritative
> that opengroup thing is, it's what google found.

It is not a BSD thing.  I searched many kernels.  I did not find the
Linux behaviour anywhere else.

> > (Linus, don't be a jerk)
> 
> I'm not the one who makes unsubstantiated statements and uses scare
> tactics to try to make said arguments sound more valid than they are.
> 
> So keep your arguments real, please.

CAN YOU PLEASE SHUT IT WITH THE PERSONAL ATTACKS?  ARE YOU SO INSECURE
THAT YOU NEED TO TAKE A TECHNICAL DISCUSSION AND MAKE IT PERSONAL?

In a new world of immutable / sealed memory, I believe there is a much
bigger problem and I would appreciate if the Linux team would give it
some consideration.

mprotect and munmap (and other calls) can now fail, due to intentional
address space manipulation requested by a process (previously).

The other previous errors have been transient system effects, like ENOMEM.

This EPERM with partial change is not transient.  A 5 line test program
can show memory which is not released, or which memory will retain
incorrect permissions.

Have any of you written test programs?