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

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Date:   Mon, 15 Apr 2019 10:46:07 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Xose Vazquez Perez <xose.vazquez@...il.com>
cc:     LKML <linux-kernel@...r.kernel.org>, x86 team <x86@...nel.org>
Subject: [PATCH] x86/mm: Prevent bogus warnings with "noexec=off"

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

__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>
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));