linux-kernel - [PATCH 10/16] x86/mm/pti: Populate valid user pud entries

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Date:   Tue, 16 Jan 2018 17:36:53 +0100
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>, jroedel@...e.de,
        joro@...tes.org
Subject: [PATCH 10/16] x86/mm/pti: Populate valid user pud entries

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

With PAE paging we don't have PGD and P4D levels in the
page-table, instead the PUD level is the highest one.

In PAE page-tables at the top-level most bits we usually set
with _KERNPG_TABLE are reserved, resulting in a #GP when
they are loaded by the processor.

Work around this by populating PUD entries in the user
page-table only with _PAGE_PRESENT set.

I am pretty sure there is a cleaner way to do this, but
until I find it use this #ifdef solution.

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

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 20be21301a59..6b6bfd13350e 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -202,8 +202,12 @@ static __init pmd_t *pti_user_pagetable_walk_pmd(unsigned long address)
 		unsigned long new_pmd_page = __get_free_page(gfp);
 		if (!new_pmd_page)
 			return NULL;
-
+#ifdef CONFIG_X86_PAE
+		/* TODO: There must be a cleaner way to do this */
+		set_pud(pud, __pud(_PAGE_PRESENT | __pa(new_pmd_page)));
+#else
 		set_pud(pud, __pud(_KERNPG_TABLE | __pa(new_pmd_page)));
+#endif
 	}
 
 	return pmd_offset(pud, address);
-- 
2.13.6