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Date: Fri, 21 Oct 2016 16:47:23 +0900
From: AKASHI Takahiro <takahiro.akashi@...aro.org>
To: Colin Vidal <colin@...dal.org>
Cc: kernel-hardening@...ts.openwall.com,
"Reshetova, Elena" <elena.reshetova@...el.com>,
David Windsor <dave@...gbits.org>,
Kees Cook <keescook@...omium.org>,
Hans Liljestrand <ishkamiel@...il.com>
Subject: Re: [RFC 0/2] arm: implementation of HARDENED_ATOMIC
On Tue, Oct 18, 2016 at 04:59:19PM +0200, Colin Vidal wrote:
> Hi,
>
> This is the first attempt of HARDENED_ATOMIC port to arm arch.
>
> About the fault handling I have some questions (perhaps some arm
> expert are reading?):
>
> - As the process that made the overflow is killed, the kernel will
> not try to go to a fixup address when the exception is raised,
> right ? Therefore, is still mandatory to add an entry in the
> __extable section?
>
> - In do_PrefetchAbort, I am unsure the code that follow the call to
> hardened_atomic_overflow is needed: the process will be killed
> anyways.
I don't know.
Even in x86 implementation, when an overflow is detected, say,
in atomic_add(), the operation is supported to be canceled
(ie. by reverting the atomic_t variable to the original value).
-Takahiro AKASHI
> I take some freedom compared to PaX patch, especially by adding some
> macro to expand functions in arm/include/asm/atomic.h.
>
> The first patch is the modification I have done is generic part to
> make it work.
>
> Otherwise, I've been stuck by ccache. When I modify do_PrefetchAbort
> in arm/mm/fault.c, ccache does not detect the update (even if the file
> is recompiled by gcc). Therefore, when I boot the new compiled kernel,
> the old version of do_PrefechAbort is called. I know do_PrefetchAbort
> is somehow special, since called by assembly code, but is still
> strange. Someone has already has this issue? The only way to solve it
> is to flush the cache...
>
> Thanks!
>
> Colin
>
> Colin Vidal (2):
> Reordering / guard definition on atomic_*_wrap function in order to
> avoid implicitly defined / redefined error on them, when
> CONFIG_HARDENED_ATOMIC is unset.
> arm: implementation for HARDENED_ATOMIC
>
> arch/arm/Kconfig | 1 +
> arch/arm/include/asm/atomic.h | 434 ++++++++++++++++++++++++++------------
> arch/arm/mm/fault.c | 15 ++
> include/asm-generic/atomic-long.h | 55 ++---
> include/linux/atomic.h | 55 +++++
> 5 files changed, 405 insertions(+), 155 deletions(-)
>
> --
> 2.7.4
>
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