[PATCH v2 09/20] x86/kprobes: instruction pages initialization enhancements
bp at alien8.de
Mon Feb 11 18:22:21 UTC 2019
> Subject: Re: [PATCH v2 09/20] x86/kprobes: instruction pages initialization enhancements
Subject needs a verb.
On Mon, Jan 28, 2019 at 04:34:11PM -0800, Rick Edgecombe wrote:
> From: Nadav Amit <namit at vmware.com>
> Make kprobes instruction pages read-only (and executable) after they are
> set to prevent them from mistaken or malicious modifications.
> This is a preparatory patch for a following patch that makes module
> allocated pages non-executable and sets the page as executable after
> While at it, do some small cleanup of what appears to be unnecessary
> Acked-by: Masami Hiramatsu <mhiramat at kernel.org>
> Signed-off-by: Nadav Amit <namit at vmware.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe at intel.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;
Null tests we generally do like this:
if (! ...
like in the rest of this file.
> + /*
> + * First make the page read-only, and then only then make it executable
s/then only then/only then/
> + * 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);
Good mailing practices for 400: avoid top-posting and trim the reply.
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