linux-kernel - [PATCH 32/35] x86/ldt: Enable LDT user-mapping for PAE

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Message-Id: <1521228593-3820-33-git-send-email-joro@8bytes.org>
Date:   Fri, 16 Mar 2018 20:29:50 +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>, Pavel Machek <pavel@....cz>,
        jroedel@...e.de, joro@...tes.org
Subject: [PATCH 32/35] x86/ldt: Enable LDT user-mapping for PAE

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

This adds the needed special case for PAE to get the LDT
mapped into the user page-table when PTI is enabled. The big
difference to the other paging modes is that we don't have a
full top-level PGD entry available for the LDT, but only PMD
entry.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 arch/x86/include/asm/mmu_context.h |  4 ---
 arch/x86/kernel/ldt.c              | 53 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index c931b88..af96cfb 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -70,11 +70,7 @@ struct ldt_struct {
 
 static inline void *ldt_slot_va(int slot)
 {
-#ifdef CONFIG_X86_64
 	return (void *)(LDT_BASE_ADDR + LDT_SLOT_STRIDE * slot);
-#else
-	BUG();
-#endif
 }
 
 /*
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
index 8ab7df9..7787451 100644
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -126,6 +126,57 @@ static void do_sanity_check(struct mm_struct *mm,
 	}
 }
 
+#ifdef CONFIG_X86_PAE
+
+static pmd_t *pgd_to_pmd_walk(pgd_t *pgd, unsigned long va)
+{
+	p4d_t *p4d;
+	pud_t *pud;
+
+	if (pgd->pgd == 0)
+		return NULL;
+
+	p4d = p4d_offset(pgd, va);
+	if (p4d_none(*p4d))
+		return NULL;
+
+	pud = pud_offset(p4d, va);
+	if (pud_none(*pud))
+		return NULL;
+
+	return pmd_offset(pud, va);
+}
+
+static void map_ldt_struct_to_user(struct mm_struct *mm)
+{
+	pgd_t *k_pgd = pgd_offset(mm, LDT_BASE_ADDR);
+	pgd_t *u_pgd = kernel_to_user_pgdp(k_pgd);
+	pmd_t *k_pmd, *u_pmd;
+
+	k_pmd = pgd_to_pmd_walk(k_pgd, LDT_BASE_ADDR);
+	u_pmd = pgd_to_pmd_walk(u_pgd, LDT_BASE_ADDR);
+
+	if (static_cpu_has(X86_FEATURE_PTI) && !mm->context.ldt)
+		set_pmd(u_pmd, *k_pmd);
+}
+
+static void sanity_check_ldt_mapping(struct mm_struct *mm)
+{
+	pgd_t *k_pgd = pgd_offset(mm, LDT_BASE_ADDR);
+	pgd_t *u_pgd = kernel_to_user_pgdp(k_pgd);
+	bool had_kernel, had_user;
+	pmd_t *k_pmd, *u_pmd;
+
+	k_pmd      = pgd_to_pmd_walk(k_pgd, LDT_BASE_ADDR);
+	u_pmd      = pgd_to_pmd_walk(u_pgd, LDT_BASE_ADDR);
+	had_kernel = (k_pmd->pmd != 0);
+	had_user   = (u_pmd->pmd != 0);
+
+	do_sanity_check(mm, had_kernel, had_user);
+}
+
+#else /* !CONFIG_X86_PAE */
+
 static void map_ldt_struct_to_user(struct mm_struct *mm)
 {
 	pgd_t *pgd = pgd_offset(mm, LDT_BASE_ADDR);
@@ -143,6 +194,8 @@ static void sanity_check_ldt_mapping(struct mm_struct *mm)
 	do_sanity_check(mm, had_kernel, had_user);
 }
 
+#endif /* CONFIG_X86_PAE */
+
 /*
  * If PTI is enabled, this maps the LDT into the kernelmode and
  * usermode tables for the given mm.
-- 
2.7.4