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Message-Id: <20180831134635.35b6c2a919449adf4b63a133@kernel.org>
Date: Fri, 31 Aug 2018 13:46:35 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Nadav Amit <namit@...are.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
<linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>,
<x86@...nel.org>, Arnd Bergmann <arnd@...db.de>,
<linux-arch@...r.kernel.org>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Andy Lutomirski <luto@...nel.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Kees Cook <keescook@...omium.org>,
Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 0/6] x86/alternatives: text_poke() fixes
On Thu, 30 Aug 2018 10:32:12 -0700
Nadav Amit <namit@...are.com> wrote:
> This patch-set addresses some issues that were raised in a recent
> correspondence and might affect the security and the correctness of code
> patching. (Note that patching performance is not addressed by this
> patch-set).
>
> The main issue that the patches deal with is the fact that the fixmap
> PTEs that are used for patching are available for access from other
> cores and might be exploited. They are not even flushed from the TLB in
> remote cores, so the risk is even higher. Address this issue by
> introducing a temporary mm that is only used during patching.
> Unfortunately, due to init ordering, fixmap is still used during
> boot-time patching. Future patches can eliminate the need for it.
>
> The second issue is the missing lockdep assertion to ensure text_mutex
> is taken. It is actually not always taken, so fix the instances that
> were found not to take the lock (although they should be safe even
> without taking the lock).
>
> Finally, try to be more conservative and to map a single page, instead
> of two, when possible. This helps both security and performance.
>
> In addition, there is some cleanup of the patching code to make it more
> readable.
OK, this series looks good to me, and tested with ftracetest, kprobe testsets.
Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>
Tested-by: Masami Hiramatsu <mhiramat@...nel.org>
Thank you!
>
> RFC->v1:
> - Added handling of error in get_locked_pte()
> - Remove lockdep assertion, clarify text_mutex use instead [masami]
> - Comment fix [peterz]
> - Removed remainders of text_poke return value [masami]
> - Use __weak for poking_init instead of macros [masami]
> - Simplify error handling in poking_init [masami]
>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Link: https://lkml.org/lkml/2018/8/24/586
>
> Andy Lutomirski (1):
> x86/mm: temporary mm struct
>
> Nadav Amit (5):
> x86/alternatives: clarify text_mutex use in text_poke
> fork: provide a function for copying init_mm
> x86/alternatives: initializing temporary mm for patching
> x86/alternatives: use temporary mm for text poking
> x86/alternatives: remove text_poke() return value
>
> arch/x86/include/asm/mmu_context.h | 20 ++++
> arch/x86/include/asm/pgtable.h | 3 +
> arch/x86/include/asm/text-patching.h | 4 +-
> arch/x86/kernel/alternative.c | 173 +++++++++++++++++++++++----
> arch/x86/mm/init_64.c | 29 +++++
> include/linux/sched/task.h | 1 +
> init/main.c | 3 +
> kernel/fork.c | 24 +++-
> 8 files changed, 226 insertions(+), 31 deletions(-)
>
> --
> 2.17.1
>
--
Masami Hiramatsu <mhiramat@...nel.org>
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