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[PATCH 36/39] x86/ldt: Enable LDT user-mapping for PAE




From: Joerg Roedel <jroedel@xxxxxxx>

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@xxxxxxx>
---
 arch/x86/include/asm/mmu_context.h |  5 ----
 arch/x86/kernel/ldt.c              | 53 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index bbc796e..eeeb928 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -71,12 +71,7 @@ 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();
-	return (void *)fix_to_virt(FIX_HOLE);
-#endif
 }
 
 /*
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
index 69af9a0..733e6ac 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