linux-kernel - Re: [PATCH] x86/mm: Prevent bogus warnings with "noexec=off"

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Date:   Tue, 16 Apr 2019 00:57:06 +0200
From:   Xose Vazquez Perez <xose.vazquez@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86 team <x86@...nel.org>
Subject: Re: [PATCH] x86/mm: Prevent bogus warnings with "noexec=off"

On 4/15/19 10:46 AM, Thomas Gleixner wrote:

> Xose reported warnings when NX is disabled on the kernel command line.

Thank you for doing the dirty work.

> 
> __early_set_fixmap() triggers:
> 
>   attempted to set unsupported pgprot:    8000000000000163
>   	       	   	       bits:      8000000000000000
> 			       supported: 7fffffffffffffff
> 
>   WARNING: CPU: 0 PID: 0 at arch/x86/include/asm/pgtable.h:537
>   	   	       	    __early_set_fixmap+0xa2/0xff
> 
> because it uses __default_kernel_pte_mask to mask out unsupported bits.
> 
> Use __supported_pte_mask instead.
> 
> Disabling NX on the command line also triggers the NX warning in the page
> table mapping check:
> 
>   WARNING: CPU: 1 PID: 1 at arch/x86/mm/dump_pagetables.c:262 note_page+0x2ae/0x650
>   ....
> 
> Make the warning depend on NX set in __supported_pte_mask.
> 
> Reported-by: Xose Vazquez Perez <xose.vazquez@...il.com>

And
Tested-by: Xose Vazquez Perez <xose.vazquez@...il.com>

> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  arch/x86/mm/dump_pagetables.c |    3 ++-
>  arch/x86/mm/ioremap.c         |    2 +-
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> --- a/arch/x86/mm/dump_pagetables.c
> +++ b/arch/x86/mm/dump_pagetables.c
> @@ -259,7 +259,8 @@ static void note_wx(struct pg_state *st)
>  #endif
>  	/* Account the WX pages */
>  	st->wx_pages += npages;
> -	WARN_ONCE(1, "x86/mm: Found insecure W+X mapping at address %pS\n",
> +	WARN_ONCE(__supported_pte_mask & _PAGE_NX,
> +		  "x86/mm: Found insecure W+X mapping at address %pS\n",
>  		  (void *)st->start_address);
>  }
>  
> --- a/arch/x86/mm/ioremap.c
> +++ b/arch/x86/mm/ioremap.c
> @@ -825,7 +825,7 @@ void __init __early_set_fixmap(enum fixe
>  	pte = early_ioremap_pte(addr);
>  
>  	/* Sanitize 'prot' against any unsupported bits: */
> -	pgprot_val(flags) &= __default_kernel_pte_mask;
> +	pgprot_val(flags) &= __supported_pte_mask;
>  
>  	if (pgprot_val(flags))
>  		set_pte(pte, pfn_pte(phys >> PAGE_SHIFT, flags));
>