linux-kernel - [PATCH 2/3] x86/mm/pti: Don't clear permissions in pti_clone

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Date:   Tue,  7 Aug 2018 12:24:30 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>, aliguori@...zon.com,
        daniel.gruss@...k.tugraz.at, hughd@...gle.com, keescook@...gle.com,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>, Pavel Machek <pavel@....cz>,
        "David H . Gutteridge" <dhgutteridge@...patico.ca>,
        jroedel@...e.de, joro@...tes.org
Subject: [PATCH 2/3] x86/mm/pti: Don't clear permissions in pti_clone_pmd()

From: Joerg Roedel <jroedel@...e.de>

The function sets the global-bit on cloned PMD entries,
which only makes sense when the permissions are identical
between the user and the kernel page-table.

Further, only write-permissions are cleared for entry-text
and kernel-text sections, which are not writeable anyway.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/mm/pti.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 113ba14..5164c98 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -291,7 +291,7 @@ static void __init pti_setup_vsyscall(void) { }
 #endif
 
 static void
-pti_clone_pmds(unsigned long start, unsigned long end, pmdval_t clear)
+pti_clone_pmds(unsigned long start, unsigned long end)
 {
 	unsigned long addr;
 
@@ -352,7 +352,7 @@ pti_clone_pmds(unsigned long start, unsigned long end, pmdval_t clear)
 		 * tables will share the last-level page tables of this
 		 * address range
 		 */
-		*target_pmd = pmd_clear_flags(*pmd, clear);
+		*target_pmd = *pmd;
 	}
 }
 
@@ -398,7 +398,7 @@ static void __init pti_clone_user_shared(void)
 	start = CPU_ENTRY_AREA_BASE;
 	end   = start + (PAGE_SIZE * CPU_ENTRY_AREA_PAGES);
 
-	pti_clone_pmds(start, end, 0);
+	pti_clone_pmds(start, end);
 }
 #endif /* CONFIG_X86_64 */
 
@@ -418,8 +418,7 @@ static void __init pti_setup_espfix64(void)
 static void pti_clone_entry_text(void)
 {
 	pti_clone_pmds((unsigned long) __entry_text_start,
-			(unsigned long) __irqentry_text_end,
-		       _PAGE_RW);
+		       (unsigned long) __irqentry_text_end);
 }
 
 /*
@@ -501,7 +500,7 @@ static void pti_clone_kernel_text(void)
 	 * pti_set_kernel_image_nonglobal() did to clear the
 	 * global bit.
 	 */
-	pti_clone_pmds(start, end_clone, _PAGE_RW);
+	pti_clone_pmds(start, end_clone);
 
 	/*
 	 * pti_clone_pmds() will set the global bit in any PMDs
-- 
2.7.4