ACK: [SRU][Disco][PATCH 1/1] x86/kprobes: Set instruction page as executable

[Colin Ian King]

On 20/08/2019 15:42, Kleber Sacilotto de Souza wrote:
> From: Nadav Amit <namit at vmware.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1840750
> 
> Set the page as executable after allocation.  This patch is a
> preparatory patch for a following patch that makes module allocated
> pages non-executable.
> 
> While at it, do some small cleanup of what appears to be unnecessary
> masking.
> 
> Signed-off-by: Nadav Amit <namit at vmware.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe at intel.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz at infradead.org>
> Cc: <akpm at linux-foundation.org>
> Cc: <ard.biesheuvel at linaro.org>
> Cc: <deneen.t.dock at intel.com>
> Cc: <kernel-hardening at lists.openwall.com>
> Cc: <kristen at linux.intel.com>
> Cc: <linux_dti at icloud.com>
> Cc: <will.deacon at arm.com>
> Cc: Andy Lutomirski <luto at kernel.org>
> Cc: Borislav Petkov <bp at alien8.de>
> Cc: Dave Hansen <dave.hansen at linux.intel.com>
> Cc: H. Peter Anvin <hpa at zytor.com>
> Cc: Linus Torvalds <torvalds at linux-foundation.org>
> Cc: Rik van Riel <riel at surriel.com>
> Cc: Thomas Gleixner <tglx at linutronix.de>
> Link: https://lkml.kernel.org/r/20190426001143.4983-11-namit@vmware.com
> Signed-off-by: Ingo Molnar <mingo at kernel.org>
> (cherry picked from commit 7298e24f904224fa79eb8fd7e0fbd78950ccf2db)
> Signed-off-by: Kleber Sacilotto de Souza <kleber.souza at canonical.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 f4b954ff5b89..3bc4cc70f1e5 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)
> +		return NULL;
> +
> +	/*
> +	 * First make the page read-only, and 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 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);
>  }
>  
> 

Clean upstream cherry pick, addresses the issue.

Acked-by: Colin Ian King <colin.king at canonical.com>