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SubjectRe: [PATCH 3/5] lguest: avoid accidental recycling of pgdir pages
Rusty Russell wrote:
> Impact: potential bugfix
>
> In theory, the kernel could reuse the same page as pgdir for a new process
> while the hypervisor keeps it cached. This would have undesirable results.
>

You can't just do this in tlb flush?

J
> Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
> ---
> arch/x86/include/asm/lguest_hcall.h | 1 +
> arch/x86/lguest/boot.c | 8 ++++++++
> drivers/lguest/hypercalls.c | 3 +++
> drivers/lguest/lg.h | 1 +
> drivers/lguest/page_tables.c | 16 ++++++++++++++++
> 5 files changed, 29 insertions(+)
>
> diff --git a/drivers/lguest/hypercalls.c b/drivers/lguest/hypercalls.c
> index 54d66f0..a160894 100644
> --- a/drivers/lguest/hypercalls.c
> +++ b/drivers/lguest/hypercalls.c
> @@ -92,6 +92,9 @@ static void do_hcall(struct lg_cpu *cpu, struct hcall_args *args)
> case LHCALL_NOTIFY:
> cpu->pending_notify = args->arg1;
> break;
> + case LHCALL_INVALIDATE_PGTABLE:
> + invalidate_pagetable(cpu, args->arg1);
> + break;
> default:
> /* It should be an architecture-specific hypercall. */
> if (lguest_arch_do_hcall(cpu, args))
> diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c
> index 65f0b8a..c3bdf0b 100644
> --- a/arch/x86/lguest/boot.c
> +++ b/arch/x86/lguest/boot.c
> @@ -540,6 +551,13 @@ static void lguest_flush_tlb_kernel(void)
> lazy_hcall(LHCALL_FLUSH_TLB, 1, 0, 0);
> }
>
> +/* This routine is called when a process exits, and we're throwing away the
> + * page table. */
> +static void lguest_pgd_free(struct mm_struct *mm, pgd_t *pgd)
> +{
> + lazy_hcall(LHCALL_INVALIDATE_PGTABLE, __pa(pgd), 0, 0);
> +}
> +
> /*
> * The Unadvanced Programmable Interrupt Controller.
> *
> @@ -1018,6 +1046,7 @@ __init void lguest_init(void)
> pv_mmu_ops.lazy_mode.leave = lguest_leave_lazy_mode;
> pv_mmu_ops.pte_update = lguest_pte_update;
> pv_mmu_ops.pte_update_defer = lguest_pte_update;
> + pv_mmu_ops.pgd_free = lguest_pgd_free;
>
> #ifdef CONFIG_X86_LOCAL_APIC
> /* apic read/write intercepts */
> diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h
> index 5faefea..363c231 100644
> --- a/drivers/lguest/lg.h
> +++ b/drivers/lguest/lg.h
> @@ -174,6 +174,7 @@ void guest_set_pte(struct lg_cpu *cpu, unsigned long gpgdir,
> unsigned long vaddr, pte_t val);
> void map_switcher_in_guest(struct lg_cpu *cpu, struct lguest_pages *pages);
> int demand_page(struct lg_cpu *cpu, unsigned long cr2, int errcode);
> +void invalidate_pagetable(struct lg_cpu *cpu, unsigned long pgtable);
> void pin_page(struct lg_cpu *cpu, unsigned long vaddr);
> unsigned long guest_pa(struct lg_cpu *cpu, unsigned long vaddr);
> void page_table_guest_data_init(struct lg_cpu *cpu);
> diff --git a/drivers/lguest/page_tables.c b/drivers/lguest/page_tables.c
> index 81d0c60..fd3e1f5 100644
> --- a/drivers/lguest/page_tables.c
> +++ b/drivers/lguest/page_tables.c
> @@ -448,6 +571,22 @@ void guest_new_pagetable(struct lg_cpu *cpu, unsigned long pgtable)
> pin_stack_pages(cpu);
> }
>
> +/* The Guest tells us when a page is no longer being used as a pagetable.
> + * Without this there can be a subtle bug where the same page gets re-used
> + * for a different process, and we think it's the same one as the one we have
> + * in our little pgdir cache. */
> +void invalidate_pagetable(struct lg_cpu *cpu, unsigned long pgtable)
> +{
> + unsigned int pgdir = find_pgdir(cpu->lg, pgtable);
> +
> + if (pgdir != ARRAY_SIZE(cpu->lg->pgdirs)) {
> + if (pgdir == cpu->cpu_pgd)
> + kill_guest(cpu, "Attempt to invalidate in-use pgdir");
> + /* We set it to an invalid value. */
> + cpu->lg->pgdirs[pgdir].gpgdir = -1UL;
> + }
> +}
> +
> /*H:470 Finally, a routine which throws away everything: all PGD entries in all
> * the shadow page tables, including the Guest's kernel mappings. This is used
> * when we destroy the Guest. */
> diff --git a/arch/x86/include/asm/lguest_hcall.h b/arch/x86/include/asm/lguest_hcall.h
> index 8f034ba..3e200ea 100644
> --- a/arch/x86/include/asm/lguest_hcall.h
> +++ b/arch/x86/include/asm/lguest_hcall.h
> @@ -17,6 +17,7 @@
> #define LHCALL_SET_PMD 15
> #define LHCALL_LOAD_TLS 16
> #define LHCALL_NOTIFY 17
> +#define LHCALL_INVALIDATE_PGTABLE 18
>
> #define LGUEST_TRAP_ENTRY 0x1F
>
>
> _______________________________________________
> Virtualization mailing list
> Virtualization@lists.linux-foundation.org
> https://lists.linux-foundation.org/mailman/listinfo/virtualization
>



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