linux-kernel - Re: [PATCH] arm64: ftrace: stop using kstop

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20151202123654.GC4523@arm.com>
Date:	Wed, 2 Dec 2015 12:36:55 +0000
From:	Will Deacon <will.deacon@....com>
To:	Li Bin <huawei.libin@...wei.com>
Cc:	rostedt@...dmis.org, mingo@...hat.com, catalin.marinas@....com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	guohanjun@...wei.com, dingtianhong@...wei.com
Subject: Re: [PATCH] arm64: ftrace: stop using kstop_machine to
 enable/disable tracing

On Sat, Nov 28, 2015 at 03:50:09PM +0800, Li Bin wrote:
> On arm64, kstop_machine which is hugely disruptive to a running
> system is not needed to convert nops to ftrace calls or back,
> because that modifed code is a single 32bit instructions which
> is impossible to cross cache (or page) boundaries, and the used str
> instruction is single-copy atomic.

This commit message is misleading, since the single-copy atomicity
guarantees don't apply to the instruction-side. Instead, the architecture
calls out a handful of safe instructions in "Concurrent modification and
execution of instructions".

Now, those safe instructions *do* include NOP, B and BL, so that should
be sufficient for ftrace provided that we don't patch condition codes
(and I don't think we do).

> Cc: <stable@...r.kernel.org> # 3.18+

I don't think this is stable material.

Will

> Signed-off-by: Li Bin <huawei.libin@...wei.com>
> ---
>  arch/arm64/kernel/ftrace.c |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
> index c851be7..9669b33 100644
> --- a/arch/arm64/kernel/ftrace.c
> +++ b/arch/arm64/kernel/ftrace.c
> @@ -93,6 +93,11 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
>  	return ftrace_modify_code(pc, old, new, true);
>  }
>  
> +void arch_ftrace_update_code(int command)
> +{
> +	ftrace_modify_all_code(command);
> +}
> +
>  int __init ftrace_dyn_arch_init(void)
>  {
>  	return 0;
> -- 
> 1.7.1
> 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/