linux-kernel - [PATCH 28/39] x86/mm/pti: Keep permissions when cloning kernel text in pti_clone_kernel

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Date:   Wed, 18 Jul 2018 11:41:05 +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 28/39] x86/mm/pti: Keep permissions when cloning kernel text in pti_clone_kernel_text()

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

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>
---
 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 4f6e933..fc77054 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);
 }
 
 /*
-- 
2.7.4