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Message-Id: <20190117155122.46058c707d6d07237ad913d0@kernel.org>
Date: Thu, 17 Jan 2019 15:51:22 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc: Andy Lutomirski <luto@...nel.org>, Ingo Molnar <mingo@...hat.com>,
linux-kernel@...r.kernel.org, x86@...nel.org, hpa@...or.com, Thomas
Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>, Nadav Amit
<nadav.amit@...il.com>, Dave Hansen <dave.hansen@...ux.intel.com>, Peter
Zijlstra <peterz@...radead.org>, linux_dti@...oud.com,
linux-integrity@...r.kernel.org, linux-security-module@...r.kernel.org,
akpm@...ux-foundation.org, kernel-hardening@...ts.openwall.com,
linux-mm@...ck.org, will.deacon@....com, ard.biesheuvel@...aro.org,
kristen@...ux.intel.com, deneen.t.dock@...el.com, Nadav Amit
<namit@...are.com>, Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH 09/17] x86/kprobes: Instruction pages initialization
enhancements
On Wed, 16 Jan 2019 16:32:51 -0800
Rick Edgecombe <rick.p.edgecombe@...el.com> wrote:
> From: Nadav Amit <namit@...are.com>
>
> This patch is a preparatory patch for a following patch that makes
> module allocated pages non-executable. The patch sets the page as
> executable after allocation.
>
> In the future, we may get better protection of executables. For example,
> by using hypercalls to request the hypervisor to protect VM executable
> pages from modifications using nested page-tables. This would allow
> us to ensure the executable has not changed between allocation and
> its write-protection.
>
> While at it, do some small cleanup of what appears to be unnecessary
> masking.
>
OK, then this should be done.
Acked-by: Masami Hiramatsu <mhiramat@...nel.org>
Thank you!
> Cc: Masami Hiramatsu <mhiramat@...nel.org>
> Signed-off-by: Nadav Amit <namit@...are.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> ---
> arch/x86/kernel/kprobes/core.c | 24 ++++++++++++++++++++----
> 1 file changed, 20 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
> index 4ba75afba527..fac692e36833 100644
> --- a/arch/x86/kernel/kprobes/core.c
> +++ b/arch/x86/kernel/kprobes/core.c
> @@ -431,8 +431,20 @@ void *alloc_insn_page(void)
> void *page;
>
> page = module_alloc(PAGE_SIZE);
> - if (page)
> - set_memory_ro((unsigned long)page & PAGE_MASK, 1);
> + if (page == NULL)
> + return NULL;
> +
> + /*
> + * First make the page read-only, and then only then make it executable
> + * to prevent it from being W+X in between.
> + */
> + set_memory_ro((unsigned long)page, 1);
> +
> + /*
> + * TODO: Once additional kernel code protection mechanisms are set, ensure
> + * that the page was not maliciously altered and it is still zeroed.
> + */
> + set_memory_x((unsigned long)page, 1);
>
> return page;
> }
> @@ -440,8 +452,12 @@ void *alloc_insn_page(void)
> /* Recover page to RW mode before releasing it */
> void free_insn_page(void *page)
> {
> - set_memory_nx((unsigned long)page & PAGE_MASK, 1);
> - set_memory_rw((unsigned long)page & PAGE_MASK, 1);
> + /*
> + * First make the page non-executable, and then only then make it
> + * writable to prevent it from being W+X in between.
> + */
> + set_memory_nx((unsigned long)page, 1);
> + set_memory_rw((unsigned long)page, 1);
> module_memfree(page);
> }
>
> --
> 2.17.1
>
--
Masami Hiramatsu <mhiramat@...nel.org>
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