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 <[email protected]> --- arch/x86/mm/dpt.c | 126 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 126 insertions(+) diff --git a/arch/x86/mm/dpt.c b/arch/x86/mm/dpt.c index a2f54ba00255..7a1b4cd53b03 100644 --- a/arch/x86/mm/dpt.c +++ b/arch/x86/mm/dpt.c @@ -258,6 +258,132 @@ static p4d_t *dpt_p4d_alloc(struct dpt *dpt, pgd_t *pgd, unsigned long addr) return p4d; } +/* + * dpt_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 decorated page table. Otherwise an error is + * returned. + */ + +static int dpt_set_pte(struct dpt *dpt, pte_t *pte, pte_t pte_value) +{ +#ifdef DEBUG + /* + * The pte pointer should come from dpt_pte_alloc() or dpt_pte_offset() + * both of which check if the pointer is in the decorated page table. + * So this is a paranoid check to ensure the pointer is really in the + * decorated page table. + */ + if (!dpt_valid_offset(dpt, pte)) { + pr_err("DPT %p: PTE %px not found\n", dpt, pte); + return -EINVAL; + } +#endif + set_pte(pte, pte_value); + + return 0; +} + +static int dpt_set_pmd(struct dpt *dpt, pmd_t *pmd, pmd_t pmd_value) +{ +#ifdef DEBUG + /* + * The pmd pointer should come from dpt_pmd_alloc() or dpt_pmd_offset() + * both of which check if the pointer is in the decorated page table. + * So this is a paranoid check to ensure the pointer is really in the + * decorated page table. + */ + if (!dpt_valid_offset(dpt, pmd)) { + pr_err("DPT %p: PMD %px not found\n", dpt, pmd); + return -EINVAL; + } +#endif + if (pmd_val(*pmd) == pmd_val(pmd_value)) + return 0; + + if (!pmd_none(*pmd)) { + pr_err("DPT %p: PMD %px overwriting %lx with %lx\n", + dpt, pmd, pmd_val(*pmd), pmd_val(pmd_value)); + return -EBUSY; + } + + set_pmd(pmd, pmd_value); + + return 0; +} + +static int dpt_set_pud(struct dpt *dpt, pud_t *pud, pud_t pud_value) +{ +#ifdef DEBUG + /* + * The pud pointer should come from dpt_pud_alloc() or dpt_pud_offset() + * both of which check if the pointer is in the decorated page table. + * So this is a paranoid check to ensure the pointer is really in the + * decorated page table. + */ + if (!dpt_valid_offset(dpt, pud)) { + pr_err("DPT %p: PUD %px not found\n", dpt, pud); + return -EINVAL; + } +#endif + if (pud_val(*pud) == pud_val(pud_value)) + return 0; + + if (!pud_none(*pud)) { + pr_err("DPT %p: PUD %px overwriting %lx with %lx\n", + dpt, pud, pud_val(*pud), pud_val(pud_value)); + return -EBUSY; + } + + set_pud(pud, pud_value); + + return 0; +} + +static int dpt_set_p4d(struct dpt *dpt, p4d_t *p4d, p4d_t p4d_value) +{ +#ifdef DEBUG + /* + * The p4d pointer should come from dpt_p4d_alloc() or dpt_p4d_offset() + * both of which check if the pointer is in the decorated page table. + * So this is a paranoid check to ensure the pointer is really in the + * decorated page table. + */ + if (!dpt_valid_offset(dpt, p4d)) { + pr_err("DPT %p: P4D %px not found\n", dpt, p4d); + return -EINVAL; + } +#endif + if (p4d_val(*p4d) == p4d_val(p4d_value)) + return 0; + + if (!p4d_none(*p4d)) { + pr_err("DPT %p: P4D %px overwriting %lx with %lx\n", + dpt, p4d, p4d_val(*p4d), p4d_val(p4d_value)); + return -EBUSY; + } + + set_p4d(p4d, p4d_value); + + return 0; +} + +static int dpt_set_pgd(struct dpt *dpt, pgd_t *pgd, pgd_t pgd_value) +{ + if (pgd_val(*pgd) == pgd_val(pgd_value)) + return 0; + + if (!pgd_none(*pgd)) { + pr_err("DPT %p: PGD %px overwriting %lx with %lx\n", + dpt, pgd, pgd_val(*pgd), pgd_val(pgd_value)); + return -EBUSY; + } + + set_pgd(pgd, pgd_value); + + return 0; +} + /* * dpt_create - allocate a page-table and create a corresponding * decorated page-table. The page-table is allocated and aligned -- 2.18.2
