linux-kernel - Re: [patch V163 01/51] x86/mm/dump_pagetables: Check PAGE

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Message-ID: <20171218140723.3oqxzhd6dkabyueq@pd.tnic>
Date:   Mon, 18 Dec 2017 15:07:23 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirsky <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Greg KH <gregkh@...uxfoundation.org>, keescook@...gle.com,
        hughd@...gle.com, Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Rik van Riel <riel@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        David Laight <David.Laight@...lab.com>,
        Eduardo Valentin <eduval@...zon.com>, aliguori@...zon.com,
        Will Deacon <will.deacon@....com>, daniel.gruss@...k.tugraz.at
Subject: Re: [patch V163 01/51] x86/mm/dump_pagetables: Check PAGE_PRESENT
 for real

On Mon, Dec 18, 2017 at 12:42:16PM +0100, Thomas Gleixner wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> The check for a present page in printk_prot():
> 
>        if (!pgprot_val(prot)) {
>                 /* Not present */
> 
> is bogus. If a PTE is set to PAGE_NONE then the pgprot_val is not zero and
> the entry is decoded in bogus ways, e.g. as RX GLB. That is confusing when
> analyzing mapping correctness. Check for the present bit to make an
> informed decision.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  arch/x86/mm/dump_pagetables.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/arch/x86/mm/dump_pagetables.c
> +++ b/arch/x86/mm/dump_pagetables.c
> @@ -140,7 +140,7 @@ static void printk_prot(struct seq_file
>  	static const char * const level_name[] =
>  		{ "cr3", "pgd", "p4d", "pud", "pmd", "pte" };
>  
> -	if (!pgprot_val(prot)) {
> +	if (!(pgprot_val(prot) & _PAGE_PRESENT)) {

Just a minor thing: there's a local pr variable a couple of lines up
which is pgprot_val(prot). So you could do additionally:

diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c
index dd8820e5da28..1014cfb21c2c 100644
--- a/arch/x86/mm/dump_pagetables.c
+++ b/arch/x86/mm/dump_pagetables.c
@@ -140,7 +140,7 @@ static void printk_prot(struct seq_file *m, pgprot_t prot, int level, bool dmsg)
 	static const char * const level_name[] =
 		{ "cr3", "pgd", "p4d", "pud", "pmd", "pte" };
 
-	if (!(pgprot_val(prot) & _PAGE_PRESENT)) {
+	if (!(pr & _PAGE_PRESENT)) {
 		/* Not present */
 		pt_dump_cont_printf(m, dmsg, "                              ");
 	} else {
--

Regardless,

Reviewed-by: Borislav Petkov <bp@...e.de>

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--