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

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Date:   Thu, 14 Dec 2017 07:15:37 -0700
From:   "Jan Beulich" <JBeulich@...e.com>
To:     "Juergen Gross" <jgross@...e.com>
Cc:     <mingo@...e.hu>, "Thomas Gleixner" <tglx@...utronix.de>,
        "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 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.

Jan