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Message-Id: <20181204121805.4621-1-igor.stoppa@huawei.com>
Date: Tue, 4 Dec 2018 14:17:59 +0200
From: Igor Stoppa <igor.stoppa@...il.com>
To: Andy Lutomirski <luto@...capital.net>,
Kees Cook <keescook@...omium.org>,
Matthew Wilcox <willy@...radead.org>
Cc: igor.stoppa@...wei.com,
Nadav Amit <nadav.amit@...il.com>,
Peter Zijlstra <peterz@...radead.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
linux-integrity@...r.kernel.org,
kernel-hardening@...ts.openwall.com,
linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: [RFC v1 PATCH 0/6] hardening: statically allocated protected memory
This patch-set is the first-cut implementation of write-rare memory
protection, as previously agreed [1]
Its purpose it to keep data write protected kernel data which is seldom
modified.
There is no read overhead, however writing requires special operations that
are probably unsitable for often-changing data.
The use is opt-in, by applying the modifier __wr_after_init to a variable
declaration.
As the name implies, the write protection kicks in only after init() is
completed; before that moment, the data is modifiable in the usual way.
Current Limitations:
* supports only data which is allocated statically, at build time.
* supports only x86_64
* might not work for very large amount of data, since it relies on the
assumption that said data can be entirely remapped, at init.
Some notes:
- even if the code is only for x86_64, it is placed in the generic
locations, with the intention of extending it also to arm64
- the current section used for collecting wr-after-init data might need to
be moved, to work with arm64 MMU
- the functionality is in its own c and h files, for now, to ease the
introduction (and refactoring) of code dealing with dynamic allocation
- recently some updated patches were posted for live-patch on arm64 [2],
they might help with adding arm64 support here
- to avoid the risk of weakening __ro_after_init, __wr_after_init data is
in a separate set of pages, and any invocation will confirm that the
memory affected falls within this range.
I have modified rodata_test accordingly, to check als othis case.
- to avoid replicating the code which does the change of mapping, there is
only one function performing multiple, selectable, operations, such as
memcpy(), memset(). I have added also rcu_assign_pointer() as further
example. But I'm not too fond of this implementation either. I just
couldn't think of any that I would like significantly better.
- I have left out the patchset from Nadav that these patches depend on,
but it can be found here [3] (Should have I resubmitted it?)
- I am not sure what is the correct form for giving proper credit wrt the
authoring of the wr_after_init mechanism, guidance would be appreciated
- In an attempt to spam less people, I have curbed the list of recipients.
If I have omitted someone who should have been kept/added, please
add them to the thread.
[1] https://www.openwall.com/lists/kernel-hardening/2018/11/22/8
[2] https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1793199.html
[3] https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1810245.html
Signed-off-by: Igor Stoppa <igor.stoppa@...wei.com>
CC: Andy Lutomirski <luto@...capital.net>
CC: Nadav Amit <nadav.amit@...il.com>
CC: Matthew Wilcox <willy@...radead.org>
CC: Peter Zijlstra <peterz@...radead.org>
CC: Kees Cook <keescook@...omium.org>
CC: Dave Hansen <dave.hansen@...ux.intel.com>
CC: linux-integrity@...r.kernel.org
CC: kernel-hardening@...ts.openwall.com
CC: linux-mm@...ck.org
CC: linux-kernel@...r.kernel.org
Igor Stoppa (6):
[PATCH 1/6] __wr_after_init: linker section and label
[PATCH 2/6] __wr_after_init: write rare for static allocation
[PATCH 3/6] rodata_test: refactor tests
[PATCH 4/6] rodata_test: add verification for __wr_after_init
[PATCH 5/6] __wr_after_init: test write rare functionality
[PATCH 6/6] __wr_after_init: lkdtm test
drivers/misc/lkdtm/core.c | 3 +
drivers/misc/lkdtm/lkdtm.h | 3 +
drivers/misc/lkdtm/perms.c | 29 ++++++++
include/asm-generic/vmlinux.lds.h | 20 ++++++
include/linux/cache.h | 17 +++++
include/linux/prmem.h | 134 +++++++++++++++++++++++++++++++++++++
init/main.c | 2 +
mm/Kconfig | 4 ++
mm/Kconfig.debug | 9 +++
mm/Makefile | 2 +
mm/prmem.c | 124 ++++++++++++++++++++++++++++++++++
mm/rodata_test.c | 63 ++++++++++++------
mm/test_write_rare.c | 135 ++++++++++++++++++++++++++++++++++++++
13 files changed, 525 insertions(+), 20 deletions(-)
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