Messages in this thread | | | From | Zong Li <> | Date | Tue, 7 Apr 2020 17:17:22 +0800 | Subject | Re: [PATCH RFC 2/8] riscv/kaslr: introduce functions to clear page table |
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On Tue, Apr 7, 2020 at 1:09 PM Alex Ghiti <alex@ghiti.fr> wrote: > > 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. >
Yes, it's a better way. Thanks.
> Alex
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