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From: Jann Horn <jannh@google.com>
To: Kees Cook <keescook@chromium.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Elena Reshetova <elena.reshetova@intel.com>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Potapenko <glider@google.com>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	"Perla, Enrico" <enrico.perla@intel.com>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	linux-arm-kernel@lists.infradead.org,
	Linux-MM <linux-mm@kvack.org>,
	kernel list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 0/5] Optionally randomize kernel stack offset each syscall
Date: Tue, 24 Mar 2020 22:28:35 +0100	[thread overview]
Message-ID: <CAG48ez3yYkMdxEEW6sJzBC5BZSbzEZKnpWzco32p-TJx7y_srg@mail.gmail.com> (raw)
In-Reply-To: <20200324203231.64324-1-keescook@chromium.org>

On Tue, Mar 24, 2020 at 9:32 PM Kees Cook <keescook@chromium.org> wrote:
> This is a continuation and refactoring of Elena's earlier effort to add
> kernel stack base offset randomization. In the time since the previous
> discussions, two attacks[1][2] were made public that depended on stack
> determinism, so we're no longer in the position of "this is a good idea
> but we have no examples of attacks". :)
[...]
> [1] https://a13xp0p0v.github.io/2020/02/15/CVE-2019-18683.html

This one only starts using the stack's location after having parsed
it out of dmesg (which in any environment that wants to provide a
reasonable level of security really ought to be restricted to root),
right? If you give people read access to dmesg, they can leak all
sorts of pointers; not just the stack pointer, but also whatever else
happens to be in the registers at that point - which is likely to give
the attacker more ways to place controlled data at a known location.
See e.g. <https://googleprojectzero.blogspot.com/2018/09/a-cache-invalidation-bug-in-linux.html>,
which leaks the pointer to a BPF map out of dmesg.

Also, are you sure that it isn't possible to make the syscall that
leaked its stack pointer never return to userspace (via ptrace or
SIGSTOP or something like that), and therefore never realign its
stack, while keeping some controlled data present on the syscall's
stack?

> [2] https://repositorio-aberto.up.pt/bitstream/10216/125357/2/374717.pdf

That's a moderately large document; which specific part are you referencing?

WARNING: multiple messages have this Message-ID (diff)
From: Jann Horn <jannh@google.com>
To: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	the arch/x86 maintainers <x86@kernel.org>,
	kernel list <linux-kernel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	Alexander Potapenko <glider@google.com>,
	linux-arm-kernel@lists.infradead.org,
	Andy Lutomirski <luto@kernel.org>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	"Perla, Enrico" <enrico.perla@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Will Deacon <will@kernel.org>,
	Elena Reshetova <elena.reshetova@intel.com>
Subject: Re: [PATCH v2 0/5] Optionally randomize kernel stack offset each syscall
Date: Tue, 24 Mar 2020 22:28:35 +0100	[thread overview]
Message-ID: <CAG48ez3yYkMdxEEW6sJzBC5BZSbzEZKnpWzco32p-TJx7y_srg@mail.gmail.com> (raw)
In-Reply-To: <20200324203231.64324-1-keescook@chromium.org>

On Tue, Mar 24, 2020 at 9:32 PM Kees Cook <keescook@chromium.org> wrote:
> This is a continuation and refactoring of Elena's earlier effort to add
> kernel stack base offset randomization. In the time since the previous
> discussions, two attacks[1][2] were made public that depended on stack
> determinism, so we're no longer in the position of "this is a good idea
> but we have no examples of attacks". :)
[...]
> [1] https://a13xp0p0v.github.io/2020/02/15/CVE-2019-18683.html

This one only starts using the stack's location after having parsed
it out of dmesg (which in any environment that wants to provide a
reasonable level of security really ought to be restricted to root),
right? If you give people read access to dmesg, they can leak all
sorts of pointers; not just the stack pointer, but also whatever else
happens to be in the registers at that point - which is likely to give
the attacker more ways to place controlled data at a known location.
See e.g. <https://googleprojectzero.blogspot.com/2018/09/a-cache-invalidation-bug-in-linux.html>,
which leaks the pointer to a BPF map out of dmesg.

Also, are you sure that it isn't possible to make the syscall that
leaked its stack pointer never return to userspace (via ptrace or
SIGSTOP or something like that), and therefore never realign its
stack, while keeping some controlled data present on the syscall's
stack?

> [2] https://repositorio-aberto.up.pt/bitstream/10216/125357/2/374717.pdf

That's a moderately large document; which specific part are you referencing?

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  parent reply	other threads:[~2020-03-24 21:29 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-24 20:32 [PATCH v2 0/5] Optionally randomize kernel stack offset each syscall Kees Cook
2020-03-24 20:32 ` Kees Cook
2020-03-24 20:32 ` [PATCH v2 1/5] jump_label: Provide CONFIG-driven build state defaults Kees Cook
2020-03-24 20:32   ` Kees Cook
2020-03-24 22:06   ` Peter Zijlstra
2020-03-24 22:06     ` Peter Zijlstra
2020-03-24 20:32 ` [PATCH v2 2/5] init_on_alloc: Unpessimize default-on builds Kees Cook
2020-03-24 20:32   ` Kees Cook
2020-03-26 15:48   ` Alexander Potapenko
2020-03-26 15:48     ` Alexander Potapenko
2020-03-26 15:48     ` Alexander Potapenko
2020-03-24 20:32 ` [PATCH v2 3/5] stack: Optionally randomize kernel stack offset each syscall Kees Cook
2020-03-24 20:32   ` Kees Cook
2020-03-30 11:25   ` Mark Rutland
2020-03-30 11:25     ` Mark Rutland
2020-03-30 18:18     ` Kees Cook
2020-03-30 18:18       ` Kees Cook
2020-03-30 18:27     ` Kees Cook
2020-03-30 18:27       ` Kees Cook
2020-03-24 20:32 ` [PATCH v2 4/5] x86/entry: Enable random_kstack_offset support Kees Cook
2020-03-24 20:32   ` Kees Cook
2020-03-28 22:26   ` Kees Cook
2020-03-28 22:26     ` Kees Cook
2020-03-24 20:32 ` [PATCH v2 5/5] arm64: entry: " Kees Cook
2020-03-24 20:32   ` Kees Cook
2020-03-25 13:21   ` Mark Rutland
2020-03-25 13:21     ` Mark Rutland
2020-03-25 20:22     ` Kees Cook
2020-03-25 20:22       ` Kees Cook
2020-03-26 11:15       ` Mark Rutland
2020-03-26 11:15         ` Mark Rutland
2020-03-26 16:31         ` Kees Cook
2020-03-26 16:31           ` Kees Cook
2020-03-30 11:26           ` Mark Rutland
2020-03-30 11:26             ` Mark Rutland
2020-04-20 20:54   ` Will Deacon
2020-04-20 20:54     ` Will Deacon
2020-04-20 22:34     ` Kees Cook
2020-04-20 22:34       ` Kees Cook
2020-04-21  7:02       ` Will Deacon
2020-04-21  7:02         ` Will Deacon
2020-03-24 21:28 ` Jann Horn [this message]
2020-03-24 21:28   ` [PATCH v2 0/5] Optionally randomize kernel stack offset each syscall Jann Horn
2020-03-24 21:28   ` Jann Horn
2020-03-24 23:07   ` Kees Cook
2020-03-24 23:07     ` Kees Cook
2020-03-25 12:15     ` Reshetova, Elena
2020-03-25 12:15       ` Reshetova, Elena
2020-03-25 12:15       ` Reshetova, Elena
2020-03-25 20:27       ` Kees Cook
2020-03-25 20:27         ` Kees Cook
2020-03-25 20:27         ` Kees Cook
2020-03-25 23:20         ` Jann Horn
2020-03-25 23:20           ` Jann Horn
2020-03-25 23:20           ` Jann Horn
2020-03-26 17:18           ` Kees Cook
2020-03-26 17:18             ` Kees Cook
2020-03-26 17:18             ` Kees Cook

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