lkml.org 
[lkml]   [2018]   [Dec]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v7 09/14] x86/kprobes: Instruction pages initialization enhancements
On Tue, 4 Dec 2018 17:34:03 -0800
Nadav Amit <namit@vmware.com> wrote:

> 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.

Sounds interesting!

>
> While at it, do some small cleanup of what appears to be unnecessary
> masking.

Looks good to me.

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>


Thanks!

>
> Cc: Masami Hiramatsu <mhiramat@kernel.org>
> Signed-off-by: Nadav Amit <namit@vmware.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 c33b06f5faa4..ca0118d3b3e8 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@kernel.org>

\
 
 \ /
  Last update: 2018-12-06 14:10    [W:0.138 / U:0.016 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site