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Subject[RFC v2 07/26] mm/asi: Add ASI page-table entry set functions
Date
Add wrappers around the page table entry (pgd/p4d/pud/pmd) set
functions which check that an existing entry is not being
overwritten.

Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
---
arch/x86/mm/asi_pagetable.c | 124 +++++++++++++++++++++++++++++++++++++++++++
1 files changed, 124 insertions(+), 0 deletions(-)

diff --git a/arch/x86/mm/asi_pagetable.c b/arch/x86/mm/asi_pagetable.c
index 0fc6d59..e17af9e 100644
--- a/arch/x86/mm/asi_pagetable.c
+++ b/arch/x86/mm/asi_pagetable.c
@@ -270,3 +270,127 @@ static bool asi_valid_offset(struct asi *asi, void *offset)

return p4d;
}
+
+/*
+ * asi_set_pXX() functions are equivalent to kernel set_pXX() functions
+ * but, in addition, they ensure that they are not overwriting an already
+ * existing reference in the page table. Otherwise an error is returned.
+ */
+static int asi_set_pte(struct asi *asi, pte_t *pte, pte_t pte_value)
+{
+#ifdef DEBUG
+ /*
+ * The pte pointer should come from asi_pte_alloc() or asi_pte_offset()
+ * both of which check if the pointer is in the kernel isolation page
+ * table. So this is a paranoid check to ensure the pointer is really
+ * in the kernel page table.
+ */
+ if (!asi_valid_offset(asi, pte)) {
+ pr_err("ASI %p: PTE %px not found\n", asi, pte);
+ return -EINVAL;
+ }
+#endif
+ set_pte(pte, pte_value);
+
+ return 0;
+}
+
+static int asi_set_pmd(struct asi *asi, pmd_t *pmd, pmd_t pmd_value)
+{
+#ifdef DEBUG
+ /*
+ * The pmd pointer should come from asi_pmd_alloc() or asi_pmd_offset()
+ * both of which check if the pointer is in the kernel isolation page
+ * table. So this is a paranoid check to ensure the pointer is really
+ * in the kernel page table.
+ */
+ if (!asi_valid_offset(asi, pmd)) {
+ pr_err("ASI %p: PMD %px not found\n", asi, pmd);
+ return -EINVAL;
+ }
+#endif
+ if (pmd_val(*pmd) == pmd_val(pmd_value))
+ return 0;
+
+ if (!pmd_none(*pmd)) {
+ pr_err("ASI %p: PMD %px overwriting %lx with %lx\n",
+ asi, pmd, pmd_val(*pmd), pmd_val(pmd_value));
+ return -EBUSY;
+ }
+
+ set_pmd(pmd, pmd_value);
+
+ return 0;
+}
+
+static int asi_set_pud(struct asi *asi, pud_t *pud, pud_t pud_value)
+{
+#ifdef DEBUG
+ /*
+ * The pud pointer should come from asi_pud_alloc() or asi_pud_offset()
+ * both of which check if the pointer is in the kernel isolation page
+ * table. So this is a paranoid check to ensure the pointer is really
+ * in the kernel page table.
+ */
+ if (!asi_valid_offset(asi, pud)) {
+ pr_err("ASI %p: PUD %px not found\n", asi, pud);
+ return -EINVAL;
+ }
+#endif
+ if (pud_val(*pud) == pud_val(pud_value))
+ return 0;
+
+ if (!pud_none(*pud)) {
+ pr_err("ASI %p: PUD %px overwriting %lx with %lx\n",
+ asi, pud, pud_val(*pud), pud_val(pud_value));
+ return -EBUSY;
+ }
+
+ set_pud(pud, pud_value);
+
+ return 0;
+}
+
+static int asi_set_p4d(struct asi *asi, p4d_t *p4d, p4d_t p4d_value)
+{
+#ifdef DEBUG
+ /*
+ * The p4d pointer should come from asi_p4d_alloc() or asi_p4d_offset()
+ * both of which check if the pointer is in the kernel isolation page
+ * table. So this is a paranoid check to ensure the pointer is really
+ * in the kernel page table.
+ */
+ if (!asi_valid_offset(asi, p4d)) {
+ pr_err("ASI %p: P4D %px not found\n", asi, p4d);
+ return -EINVAL;
+ }
+#endif
+ if (p4d_val(*p4d) == p4d_val(p4d_value))
+ return 0;
+
+ if (!p4d_none(*p4d)) {
+ pr_err("ASI %p: P4D %px overwriting %lx with %lx\n",
+ asi, p4d, p4d_val(*p4d), p4d_val(p4d_value));
+ return -EBUSY;
+ }
+
+ set_p4d(p4d, p4d_value);
+
+ return 0;
+}
+
+static int asi_set_pgd(struct asi *asi, pgd_t *pgd, pgd_t pgd_value)
+{
+ if (pgd_val(*pgd) == pgd_val(pgd_value))
+ return 0;
+
+ if (!pgd_none(*pgd)) {
+ pr_err("ASI %p: PGD %px overwriting %lx with %lx\n",
+ asi, pgd, pgd_val(*pgd), pgd_val(pgd_value));
+ return -EBUSY;
+ }
+
+ set_pgd(pgd, pgd_value);
+
+ return 0;
+}
--
1.7.1
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