linux-kernel - Re: [PATCH 1/2] x86: consider effective protection attributes in W+X check

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Message-ID: <alpine.DEB.2.20.1712141516240.4998@nanos>
Date:   Thu, 14 Dec 2017 15:17:38 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jan Beulich <JBeulich@...e.com>
cc:     Juergen Gross <jgross@...e.com>, mingo@...e.hu,
        xen-devel <xen-devel@...ts.xenproject.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        sds@...ho.nsa.gov, linux-kernel@...r.kernel.org, hpa@...or.com
Subject: Re: [PATCH 1/2] x86: consider effective protection attributes in
 W+X check

On Thu, 14 Dec 2017, Jan Beulich wrote:
> >>> On 14.12.17 at 15:04, <jgross@...e.com> wrote:
> > On 12/12/17 11:31, Jan Beulich wrote:
> >> @@ -335,42 +346,45 @@ static inline bool kasan_page_table(stru
> >>  
> >>  #if PTRS_PER_PMD > 1
> >>  
> >> -static void walk_pmd_level(struct seq_file *m, struct pg_state *st, pud_t addr, unsigned long P)
> >> +static void walk_pmd_level(struct seq_file *m, struct pg_state *st, pud_t addr,
> >> +			   pgprotval_t eff_in, unsigned long P)
> >>  {
> >>  	int i;
> >>  	pmd_t *start, *pmd_start;
> >> -	pgprotval_t prot;
> >> +	pgprotval_t prot, eff;
> >>  
> >>  	pmd_start = start = (pmd_t *)pud_page_vaddr(addr);
> >>  	for (i = 0; i < PTRS_PER_PMD; i++) {
> >>  		st->current_address = normalize_addr(P + i * PMD_LEVEL_MULT);
> >>  		if (!pmd_none(*start)) {
> >> +			prot = pmd_flags(*start);
> >> +			eff = effective_prot(eff_in, prot);
> >>  			if (pmd_large(*start) || !pmd_present(*start)) {
> >> -				prot = pmd_flags(*start);
> >> -				note_page(m, st, __pgprot(prot), 4);
> >> +				note_page(m, st, __pgprot(prot), eff, 4);
> >>  			} else if (!kasan_page_table(m, st, pmd_start)) {
> >> -				walk_pte_level(m, st, *start,
> >> +				walk_pte_level(m, st, *start, eff,
> >>  					       P + i * PMD_LEVEL_MULT);
> >>  			}
> > 
> > You can drop the braces for both cases. Applies to similar
> > constructs below, too.
> 
> I did consider that, but decided against to allow the patch to show
> more clearly what it is that is actually being changed.
> 
> > With that fixed you can add my:
> > 
> > Reviewed-by: Juergen Gross <jgross@...e.com>
> 
> Thanks. I'd like to wait for the x86 maintainer's opinion, and hence
> won't add your R-b unless you tell me that's fine either way, or
> unless they too would prefer resulting code cleanliness over patch
> readability.

If you remove the braces the code readability degrades because it's not a
single line statement.

Thanks,

	tglx