From: Catalin Marinas <catalin.marinas@arm.com>
To: Kees Cook <keescook@chromium.org>
Cc: "Topi Miettinen" <toiwoton@gmail.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Christoph Hellwig" <hch@infradead.org>,
"Lennart Poettering" <lennart@poettering.net>,
"Zbigniew Jędrzejewski-Szmek" <zbyszek@in.waw.pl>,
"Will Deacon" <will@kernel.org>,
"Alexander Viro" <viro@zeniv.linux.org.uk>,
"Eric Biederman" <ebiederm@xmission.com>,
"Szabolcs Nagy" <szabolcs.nagy@arm.com>,
"Mark Brown" <broonie@kernel.org>,
"Jeremy Linton" <jeremy.linton@arm.com>,
linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org,
linux-abi-devel@lists.sourceforge.net,
linux-hardening@vger.kernel.org, "Jann Horn" <jannh@google.com>,
"Salvatore Mesoraca" <s.mesoraca16@gmail.com>,
"Igor Zhbanov" <izh1979@gmail.com>
Subject: Re: [PATCH RFC 0/4] mm, arm64: In-kernel support for memory-deny-write-execute (MDWE)
Date: Thu, 21 Apr 2022 19:33:05 +0100 [thread overview]
Message-ID: <YmGjYYlcSVz38rOe@arm.com> (raw)
In-Reply-To: <202204211030.B0093CC14@keescook>
On Thu, Apr 21, 2022 at 10:41:43AM -0700, Kees Cook wrote:
> On Thu, Apr 21, 2022 at 06:24:21PM +0100, Catalin Marinas wrote:
> > On Thu, Apr 21, 2022 at 09:42:23AM -0700, Kees Cook wrote:
> > > On Thu, Apr 21, 2022 at 04:35:15PM +0100, Catalin Marinas wrote:
> > > > Do we want the "was PROT_WRITE" or we just reject mprotect(PROT_EXEC) if
> > > > the vma is not already PROT_EXEC? The latter is closer to the current
> > > > systemd approach. The former allows an mprotect(PROT_EXEC) if the
> > > > mapping was PROT_READ only for example.
> > > >
> > > > I'd drop the "was PROT_WRITE" for now if the aim is a drop-in
> > > > replacement for BPF MDWE.
> > >
> > > I think "was PROT_WRITE" is an important part of the defense that
> > > couldn't be done with a simple seccomp filter (which is why the filter
> > > ended up being a problem in the first place).
> >
> > I would say "was PROT_WRITE" is slightly more relaxed than "is not
> > already PROT_EXEC". The seccomp filter can't do "is not already
> > PROT_EXEC" either since it only checks the mprotect() arguments, not the
> > current vma flags.
> >
> > So we have (with sub-cases):
> >
> > 1. Current BPF filter:
> >
> > a) mmap(PROT_READ|PROT_WRITE|PROT_EXEC); // fails
> >
> > b) mmap(PROT_READ|PROT_EXEC);
> > mprotect(PROT_READ|PROT_EXEC|PROT_BTI); // fails
> >
> > c) mmap(PROT_READ);
> > mprotect(PROT_READ|PROT_EXEC); // fails
> >
> > d) mmap(PROT_READ|PROT_WRITE);
> > mprotect(PROT_READ);
> > mprotect(PROT_READ|PROT_EXEC); // fails
> >
> > 2. "is not already PROT_EXEC":
> >
> > a) mmap(PROT_READ|PROT_WRITE|PROT_EXEC); // fails
> >
> > b) mmap(PROT_READ|PROT_EXEC);
> > mprotect(PROT_READ|PROT_EXEC|PROT_BTI); // passes
> >
> > c) mmap(PROT_READ);
> > mprotect(PROT_READ|PROT_EXEC); // fails
> >
> > d) mmap(PROT_READ|PROT_WRITE);
> > mprotect(PROT_READ);
> > mprotect(PROT_READ|PROT_EXEC); // fails
> >
> > 3. "is or was not PROT_WRITE":
> >
> > a) mmap(PROT_READ|PROT_WRITE|PROT_EXEC); // fails
> >
> > b) mmap(PROT_READ|PROT_EXEC);
> > mprotect(PROT_READ|PROT_EXEC|PROT_BTI); // passes
> >
> > c) mmap(PROT_READ);
> > mprotect(PROT_READ|PROT_EXEC); // passes
> >
> > d) mmap(PROT_READ|PROT_WRITE);
> > mprotect(PROT_READ);
> > mprotect(PROT_READ|PROT_EXEC); // fails
>
> [edited above to show each case]
Thanks, I was in a rush to get home ;).
> restated what was already summarized:
> Problem is 1.b. 2 and 3 solve it. 3 is more relaxed (c passes).
>
> > If we don't care about 3.c, we might as well go for (2). I don't mind,
> > already went for (3) in this series. I think either of them would not be
> > a regression on MDWE, unless there is some test that attempts 3.c and
> > expects it to fail.
>
> I should stop arguing for a less restrictive mode. ;) It just feels weird
> that the combinations are API-mediated, rather than logically defined:
> I can do PROT_READ|PROT_EXEC with mmap but not mprotect under 2. As
> opposed to saying "the vma cannot be executable if it is or ever was
> writable". I find the latter much easier to reason about as far as the
> expectations of system state.
I had the same reasoning, hence option 3 in this series. I prefer to
treat mmap(PROT_READ|PROT_EXEC) and mprotect(PROT_READ|PROT_EXEC) in a
similar way.
--
Catalin
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next prev parent reply other threads:[~2022-04-21 18:34 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-13 13:49 [PATCH RFC 0/4] mm, arm64: In-kernel support for memory-deny-write-execute (MDWE) Catalin Marinas
2022-04-13 13:49 ` [PATCH RFC 1/4] mm: Track previously writeable vma permission Catalin Marinas
2022-04-13 13:49 ` [PATCH RFC 2/4] mm, personality: Implement memory-deny-write-execute as a personality flag Catalin Marinas
2022-04-21 17:37 ` David Hildenbrand
2022-04-22 10:28 ` Catalin Marinas
2022-04-22 11:04 ` David Hildenbrand
2022-04-22 13:12 ` Catalin Marinas
2022-04-22 17:41 ` David Hildenbrand
2022-04-13 13:49 ` [PATCH RFC 3/4] fs/binfmt_elf: Tell user-space about the DENY_WRITE_EXEC " Catalin Marinas
2022-04-13 13:49 ` [PATCH RFC 4/4] arm64: Select ARCH_ENABLE_DENY_WRITE_EXEC Catalin Marinas
2022-04-13 18:39 ` [PATCH RFC 0/4] mm, arm64: In-kernel support for memory-deny-write-execute (MDWE) Topi Miettinen
2022-04-14 13:49 ` Catalin Marinas
2022-04-14 18:52 ` Kees Cook
2022-04-15 20:01 ` Topi Miettinen
2022-04-20 13:01 ` Catalin Marinas
2022-04-20 17:44 ` Kees Cook
2022-04-20 19:34 ` Topi Miettinen
2022-04-20 23:21 ` Kees Cook
2022-04-21 15:35 ` Catalin Marinas
2022-04-21 16:42 ` Kees Cook
2022-04-21 17:24 ` Catalin Marinas
2022-04-21 17:41 ` Kees Cook
2022-04-21 18:33 ` Catalin Marinas [this message]
2022-04-21 16:48 ` Topi Miettinen
2022-04-21 17:28 ` Catalin Marinas
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