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From: Peter Zijlstra <peterz@infradead.org>
To: Song Liu <songliubraving@fb.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	kernel-team@fb.com, stable@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Dave Hansen <dave.hansen@intel.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Andy Lutomirski <luto@amacapital.net>
Subject: Re: [PATCH] x86/mm: Do not split_large_page() for set_kernel_text_rw()
Date: Fri, 23 Aug 2019 11:36:37 +0200	[thread overview]
Message-ID: <20190823093637.GH2369@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190823052335.572133-1-songliubraving@fb.com>

On Thu, Aug 22, 2019 at 10:23:35PM -0700, Song Liu wrote:
> As 4k pages check was removed from cpa [1], set_kernel_text_rw() leads to
> split_large_page() for all kernel text pages. This means a single kprobe
> will put all kernel text in 4k pages:
> 
>   root@ ~# grep ffff81000000- /sys/kernel/debug/page_tables/kernel
>   0xffffffff81000000-0xffffffff82400000     20M  ro    PSE      x  pmd
> 
>   root@ ~# echo ONE_KPROBE >> /sys/kernel/debug/tracing/kprobe_events
>   root@ ~# echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable
> 
>   root@ ~# grep ffff81000000- /sys/kernel/debug/page_tables/kernel
>   0xffffffff81000000-0xffffffff82400000     20M  ro             x  pte
> 
> To fix this issue, introduce CPA_FLIP_TEXT_RW to bypass "Text RO" check
> in static_protections().
> 
> Two helper functions set_text_rw() and set_text_ro() are added to flip
> _PAGE_RW bit for kernel text.
> 
> [1] commit 585948f4f695 ("x86/mm/cpa: Avoid the 4k pages check completely")

ARGH; so this is because ftrace flips the whole kernel range to RW and
back for giggles? I'm thinking _that_ is a bug, it's a clear W^X
violation.

  reply	other threads:[~2019-08-23  9:37 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-23  5:23 [PATCH] x86/mm: Do not split_large_page() for set_kernel_text_rw() Song Liu
2019-08-23  9:36 ` Peter Zijlstra [this message]
2019-08-26  4:40   ` Song Liu
2019-08-26  9:23     ` Peter Zijlstra
2019-08-26 15:08       ` Song Liu
2019-08-26 20:50         ` Song Liu
2019-08-26 11:33   ` Steven Rostedt
2019-08-26 12:44     ` Peter Zijlstra
2019-08-26 15:41     ` Nadav Amit
2019-08-26 15:56       ` Peter Zijlstra
2019-08-26 15:56       ` Steven Rostedt
2019-08-26 16:09         ` Nadav Amit

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