From: Jann Horn <jann@thejh.net>
To: security@kernel.org, Alexander Viro <viro@zeniv.linux.org.uk>,
Paul Moore <paul@paul-moore.com>,
Stephen Smalley <sds@tycho.nsa.gov>,
Eric Paris <eparis@parisplace.org>,
James Morris <james.l.morris@oracle.com>,
"Serge E. Hallyn" <serge@hallyn.com>,
mchong@google.com, Andy Lutomirski <luto@amacapital.net>,
Ingo Molnar <mingo@kernel.org>, Oleg Nesterov <oleg@redhat.com>,
Nick Kralevich <nnk@google.com>,
Janis Danisevskis <jdanis@google.com>
Cc: linux-security-module@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] mm: add LSM hook for writes to readonly memory
Date: Thu, 3 Nov 2016 11:39:23 +0100 [thread overview]
Message-ID: <20161103103922.GD13748@pc.thejh.net> (raw)
In-Reply-To: <1478142286-18427-2-git-send-email-jann@thejh.net>
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On Thu, Nov 03, 2016 at 04:04:42AM +0100, Jann Horn wrote:
> SELinux attempts to make it possible to whitelist trustworthy sources of
> code that may be mapped into memory, and Android makes use of this feature.
> To prevent an attacker from bypassing this by modifying R+X memory through
> /proc/$pid/mem, PTRACE_POKETEXT or DMA, it is necessary to call a security
> hook in check_vma_flags().
>
> PTRACE_POKETEXT can also be mitigated by blocking ptrace access, and
> /proc/$pid/mem can also be blocked at the VFS layer, but DMA is harder to
> deal with: Some driver functions (e.g. videobuf_dma_init_user_locked)
> write to user-specified DMA mappings even if those mappings are readonly
> or R+X.
>
> The new security hook security_forced_write() takes three arguments:
>
> - The modified VMA, so the security check can e.g. test for executability.
> - The subject performing the access. For remote accesses, this may be
> different from the target of the access. This can e.g. be used to create
> a security policy that permits a privileged debugger to set software
> breakpoints in the address space of a sandboxed process.
> - The target of the access. This is useful if only a subset of the
> processes on the system should be prevented from executing arbitrary
> code, as is the case on Android.
>
> changed in v2:
> - fix comment (Janis Danisevsk)
> - simplify code a bit (Janis Danisevsk)
>
> changed in v3:
> - rebase
> - no need to pass in creds in populate_vma_page_range()
> - reword check_vma_flags() comment (Ingo Molnar)
> - use helper struct gup_creds (Ingo Molnar)
I introduced some bugs here again, as the kernel test robot points out.
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next prev parent reply other threads:[~2016-11-03 10:39 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-03 3:04 [PATCH 1/3] fs/exec: don't force writing memory access Jann Horn
2016-11-03 3:04 ` [PATCH 2/3] mm: add LSM hook for writes to readonly memory Jann Horn
2016-11-03 10:39 ` Jann Horn [this message]
2016-11-03 3:04 ` [PATCH 3/3] selinux: require EXECMEM for forced ptrace poke Jann Horn
2016-11-03 3:04 ` [PATCH v3 1/3] fs/exec: don't force writing memory access Jann Horn
2016-11-03 18:24 ` Oleg Nesterov
2016-11-03 3:04 ` [PATCH v3 2/3] mm: add LSM hook for writes to readonly memory Jann Horn
2016-11-03 3:10 ` Jann Horn
2016-11-03 3:04 ` [PATCH v3 3/3] selinux: require EXECMEM for forced ptrace poke Jann Horn
2016-11-03 13:21 ` Stephen Smalley
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