Messages in this thread | | | From | Alex Ghiti <> | Subject | Re: [PATCH RFC 2/8] riscv/kaslr: introduce functions to clear page table | Date | Tue, 7 Apr 2020 01:09:02 -0400 |
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On 3/24/20 3:30 AM, Zong Li wrote: > In KASLR, we need to re-create page table after getting a random > destination. Introduce clear function to clear old content. Also, the > page table entries allow writing value when it's empty, so we have to > clear the early page table. > > This patch is a preparation to support KASLR. > > Signed-off-by: Zong Li <zong.li@sifive.com> > --- > arch/riscv/mm/init.c | 54 ++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 54 insertions(+) > > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c > index ace5d74fd939..51e263c04fa2 100644 > --- a/arch/riscv/mm/init.c > +++ b/arch/riscv/mm/init.c > @@ -315,6 +315,7 @@ static void __init create_pmd_mapping(pmd_t *pmdp, > #define get_pgd_next_virt(__pa) get_pmd_virt(__pa) > #define create_pgd_next_mapping(__nextp, __va, __pa, __sz, __prot) \ > create_pmd_mapping(__nextp, __va, __pa, __sz, __prot) > +#define clear_pgd_next_mapping(__nextp) clear_pmd(__nextp) > #define fixmap_pgd_next fixmap_pmd > #else > #define pgd_next_t pte_t > @@ -322,6 +323,7 @@ static void __init create_pmd_mapping(pmd_t *pmdp, > #define get_pgd_next_virt(__pa) get_pte_virt(__pa) > #define create_pgd_next_mapping(__nextp, __va, __pa, __sz, __prot) \ > create_pte_mapping(__nextp, __va, __pa, __sz, __prot) > +#define clear_pgd_next_mapping(__nextp) clear_pte(__nextp) > #define fixmap_pgd_next fixmap_pte > #endif > > @@ -361,6 +363,58 @@ static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size) > return PMD_SIZE; > } > > +#ifdef CONFIG_RANDOMIZE_BASE > +static void __init clear_pte(pte_t *ptep) > +{ > + unsigned int i; > + > + for (i = 0; i < PTRS_PER_PTE; i++) > + if (!pte_none(ptep[i])) > + ptep[i] = __pte(0); > +} > + > +static void __init clear_pmd(pmd_t *pmdp) > +{ > + unsigned int i; > + pte_t *ptep; > + phys_addr_t pte_phys; > + uintptr_t kaslr_offset = get_kaslr_offset(); > + > + for (i = 0; i < PTRS_PER_PMD; i++) > + if (!pmd_none(pmdp[i])) { > + if (pmd_leaf(pmdp[i])) { > + pmd_clear(&pmdp[i]); > + } else { > + pte_phys = PFN_PHYS(_pmd_pfn(pmdp[i])); > + ptep = get_pte_virt(pte_phys + kaslr_offset); > + clear_pte(ptep); > + pmd_clear(&pmdp[i]); > + } > + } > +} > + > +static void __init clear_pgd(pgd_t *pgdp) > +{ > + unsigned int i; > + pgd_next_t *nextp; > + phys_addr_t next_phys; > + uintptr_t kaslr_offset = get_kaslr_offset(); > + > + for (i = 0; i < PTRS_PER_PGD; i++) > + if (pgd_val(pgdp[i]) != 0) { > + if (pgd_leaf(pgd_val(pgdp[i]))) { > + set_pgd(&pgdp[i], __pgd(0)); > + } else { > + next_phys = PFN_PHYS(_pgd_pfn(pgdp[i])); > + nextp = get_pgd_next_virt(next_phys + > + kaslr_offset); > + clear_pgd_next_mapping(nextp); > + set_pgd(&pgdp[i], __pgd(0)); > + } > + } > +} > +#endif > + > /* > * setup_vm() is called from head.S with MMU-off. > * >
If this is only for clearing early page tables, a memset is way easier as there is only one page per level to clear.
Alex
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