linux-kernel - [tip:x86/pti] x86/mm/pti: Clone CPU_ENTRY_AREA on PMD level on x86

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Date:   Thu, 19 Jul 2018 16:32:10 -0700
From:   tip-bot for Joerg Roedel <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     aarcange@...hat.com, peterz@...radead.org,
        gregkh@...uxfoundation.org, dvlasenk@...hat.com,
        tglx@...utronix.de, hpa@...or.com, llong@...hat.com,
        dave.hansen@...el.com, torvalds@...ux-foundation.org,
        jpoimboe@...hat.com, eduval@...zon.com, mingo@...nel.org,
        brgerst@...il.com, luto@...nel.org, jgross@...e.com,
        boris.ostrovsky@...cle.com, bp@...en8.de, will.deacon@....com,
        linux-kernel@...r.kernel.org, dhgutteridge@...patico.ca,
        David.Laight@...lab.com, jroedel@...e.de, jkosina@...e.cz,
        pavel@....cz
Subject: [tip:x86/pti] x86/mm/pti: Clone CPU_ENTRY_AREA on PMD level on
 x86_32

Commit-ID:  f94560cd6b5117f8913f4c42f4d9a405c26ddc1c
Gitweb:     https://git.kernel.org/tip/f94560cd6b5117f8913f4c42f4d9a405c26ddc1c
Author:     Joerg Roedel <jroedel@...e.de>
AuthorDate: Wed, 18 Jul 2018 11:41:03 +0200
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Fri, 20 Jul 2018 01:11:44 +0200

x86/mm/pti: Clone CPU_ENTRY_AREA on PMD level on x86_32

Cloning on the P4D level would clone the complete kernel address space into
the user-space page-tables for PAE kernels. Cloning on PMD level is fine
for PAE and legacy paging.

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/1531906876-13451-27-git-send-email-joro@8bytes.org

---
 arch/x86/mm/pti.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 79217868dd13..a594e3b6401a 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -348,6 +348,7 @@ pti_clone_pmds(unsigned long start, unsigned long end, pmdval_t clear)
 	}
 }

+#ifdef CONFIG_X86_64
 /*
  * Clone a single p4d (i.e. a top-level entry on 4-level systems and a
  * next-level entry on 5-level systems.
@@ -371,6 +372,25 @@ static void __init pti_clone_user_shared(void)
 	pti_clone_p4d(CPU_ENTRY_AREA_BASE);
 }

+#else /* CONFIG_X86_64 */
+
+/*
+ * On 32 bit PAE systems with 1GB of Kernel address space there is only
+ * one pgd/p4d for the whole kernel. Cloning that would map the whole
+ * address space into the user page-tables, making PTI useless. So clone
+ * the page-table on the PMD level to prevent that.
+ */
+static void __init pti_clone_user_shared(void)
+{
+	unsigned long start, end;
+
+	start = CPU_ENTRY_AREA_BASE;
+	end   = start + (PAGE_SIZE * CPU_ENTRY_AREA_PAGES);
+
+	pti_clone_pmds(start, end, 0);
+}
+#endif /* CONFIG_X86_64 */
+
 /*
  * Clone the ESPFIX P4D into the user space visible page table
  */