linux-kernel - [tip:x86/pti] x86/mm/pti: Keep permissions when cloning kernel text in pti_clone_kernel

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Date:   Thu, 19 Jul 2018 16:33:15 -0700
From:   tip-bot for Joerg Roedel <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     torvalds@...ux-foundation.org, jpoimboe@...hat.com,
        dave.hansen@...el.com, tglx@...utronix.de, peterz@...radead.org,
        pavel@....cz, bp@...en8.de, luto@...nel.org, mingo@...nel.org,
        boris.ostrovsky@...cle.com, jkosina@...e.cz, aarcange@...hat.com,
        David.Laight@...lab.com, hpa@...or.com, dvlasenk@...hat.com,
        will.deacon@....com, jgross@...e.com, linux-kernel@...r.kernel.org,
        dhgutteridge@...patico.ca, llong@...hat.com, brgerst@...il.com,
        jroedel@...e.de, eduval@...zon.com, gregkh@...uxfoundation.org
Subject: [tip:x86/pti] x86/mm/pti: Keep permissions when cloning kernel text
 in pti_clone_kernel_text()

Commit-ID:  1ac228a7c87f697d1d01eb6362a6b5246705b0dd
Gitweb:     https://git.kernel.org/tip/1ac228a7c87f697d1d01eb6362a6b5246705b0dd
Author:     Joerg Roedel <jroedel@...e.de>
AuthorDate: Wed, 18 Jul 2018 11:41:05 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Fri, 20 Jul 2018 01:11:45 +0200

x86/mm/pti: Keep permissions when cloning kernel text in pti_clone_kernel_text()

Mapping the kernel text area to user-space makes only sense if it has the
same permissions as in the kernel page-table.  If permissions are different
this will cause a TLB reload when using the kernel page-table, which is as
good as not mapping it at all.

On 64-bit kernels this patch makes no difference, as the whole range cloned
by pti_clone_kernel_text() is mapped RO anyway. On 32 bit there are
writeable mappings in the range, so just keep the permissions as they are.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Pavel Machek <pavel@....cz>
Cc: "H . Peter Anvin" <hpa@...or.com>
Cc: linux-mm@...ck.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Juergen Gross <jgross@...e.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Jiri Kosina <jkosina@...e.cz>
Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: Brian Gerst <brgerst@...il.com>
Cc: David Laight <David.Laight@...lab.com>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Eduardo Valentin <eduval@...zon.com>
Cc: Greg KH <gregkh@...uxfoundation.org>
Cc: Will Deacon <will.deacon@....com>
Cc: aliguori@...zon.com
Cc: daniel.gruss@...k.tugraz.at
Cc: hughd@...gle.com
Cc: keescook@...gle.com
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: Waiman Long <llong@...hat.com>
Cc: "David H . Gutteridge" <dhgutteridge@...patico.ca>
Cc: joro@...tes.org
Link: https://lkml.kernel.org/r/1531906876-13451-29-git-send-email-joro@8bytes.org

---
 arch/x86/mm/pti.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 453d23760941..e41ee93c430d 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -482,7 +482,7 @@ void pti_clone_kernel_text(void)
 	 * pti_set_kernel_image_nonglobal() did to clear the
 	 * global bit.
 	 */
-	pti_clone_pmds(start, end, _PAGE_RW);
+	pti_clone_pmds(start, end, 0);
 }

 /*