Re: [PATCH v2 05/13] arm64: kvm: deal with kernel symbols outside of linear mapping

Marc Zyngier
2016-01-04T11:03:09Z

On 04/01/16 10:31, Ard Biesheuvel wrote:
> On 4 January 2016 at 11:08, Marc Zyngier <marc.zyngier@arm.com> wrote:
>> Hi Ard,
>>
>> On 30/12/15 15:26, Ard Biesheuvel wrote:
>>> KVM on arm64 uses a fixed offset between the linear mapping at EL1 and
>>> the HYP mapping at EL2. Before we can move the kernel virtual mapping
>>> out of the linear mapping, we have to make sure that references to kernel
>>> symbols that are accessed via the HYP mapping are translated to their
>>> linear equivalent.
>>>
>>> To prevent inadvertent direct references from sneaking in later, change
>>> the type of all extern declarations to HYP kernel symbols to the opaque
>>> 'struct kvm_ksym', which does not decay to a pointer type like char arrays
>>> and function references. This is not bullet proof, but at least forces the
>>> user to take the address explicitly rather than referencing it directly.
>>>
>>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>>
>> This looks good to me, a few comments below.
>>
>>> ---
>>> arch/arm/include/asm/kvm_asm.h | 2 ++
>>> arch/arm/include/asm/kvm_mmu.h | 2 ++
>>> arch/arm/kvm/arm.c | 9 +++++----
>>> arch/arm/kvm/mmu.c | 12 +++++------
>>> arch/arm64/include/asm/kvm_asm.h | 21 +++++++++++---------
>>> arch/arm64/include/asm/kvm_mmu.h | 2 ++
>>> arch/arm64/include/asm/virt.h | 4 ----
>>> arch/arm64/kernel/vmlinux.lds.S | 4 ++--
>>> arch/arm64/kvm/debug.c | 4 +++-
>>> virt/kvm/arm/vgic-v3.c | 2 +-
>>> 10 files changed, 34 insertions(+), 28 deletions(-)
>>>
>>> diff --git a/arch/arm/include/asm/kvm_asm.h b/arch/arm/include/asm/kvm_asm.h
>>> index 194c91b610ff..484ffdf7c70b 100644
>>> --- a/arch/arm/include/asm/kvm_asm.h
>>> +++ b/arch/arm/include/asm/kvm_asm.h
>>> @@ -99,6 +99,8 @@ extern void __kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa);
>>> extern void __kvm_tlb_flush_vmid(struct kvm *kvm);
>>>
>>> extern int __kvm_vcpu_run(struct kvm_vcpu *vcpu);
>>> +
>>> +extern char __hyp_idmap_text_start[], __hyp_idmap_text_end[];
>>> #endif
>>>
>>> #endif /* __ARM_KVM_ASM_H__ */
>>> diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
>>> index 405aa1883307..412b363f79e9 100644
>>> --- a/arch/arm/include/asm/kvm_mmu.h
>>> +++ b/arch/arm/include/asm/kvm_mmu.h
>>> @@ -30,6 +30,8 @@
>>> #define HYP_PAGE_OFFSET PAGE_OFFSET
>>> #define KERN_TO_HYP(kva) (kva)
>>>
>>> +#define kvm_ksym_ref(kva) (kva)
>>> +
>>> /*
>>> * Our virtual mapping for the boot-time MMU-enable code. Must be
>>> * shared across all the page-tables. Conveniently, we use the vectors
>>> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
>>> index e06fd299de08..014b542ea658 100644
>>> --- a/arch/arm/kvm/arm.c
>>> +++ b/arch/arm/kvm/arm.c
>>> @@ -427,7 +42You can use it, but you don't have to, since yo7,7 @@ static void update_vttbr(struct kvm *kvm)
>>> * shareable domain to make sure all data structures are
>>> * clean.
>>> */
>>> - kvm_call_hyp(__kvm_flush_vm_context);
>>> + kvm_call_hyp(kvm_ksym_ref(__kvm_flush_vm_context));
>>> }
>>>
>>> kvm->arch.vmid_gen = atomic64_read(&kvm_vmid_gen);
>>> @@ -600,7 +600,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run)
>>> __kvm_guest_enter();
>>> vcpu->mode = IN_GUEST_MODE;
>>>
>>> - ret = kvm_call_hyp(__kvm_vcpu_run, vcpu);
>>> + ret = kvm_call_hyp(kvm_ksym_ref(__kvm_vcpu_run), vcpu);
>>>
>>> vcpu->mode = OUTSIDE_GUEST_MODE;
>>> /*
>>> @@ -969,7 +969,7 @@ static void cpu_init_hyp_mode(void *dummy)
>>> pgd_ptr = kvm_mmu_get_httbr();
>>> stack_page = __this_cpu_read(kvm_arm_hyp_stack_page);
>>> hyp_stack_ptr = stack_page + PAGE_SIZE;
>>> - vector_ptr = (unsigned long)__kvm_hyp_vector;
>>> + vector_ptr = (unsigned long)kvm_ksym_ref(__kvm_hyp_vector);
>>>
>>> __cpu_init_hyp_mode(boot_pgd_ptr, pgd_ptr, hyp_stack_ptr, vector_ptr);
>>>
>>> @@ -1061,7 +1061,8 @@ static int init_hyp_mode(void)
>>> /*
>>> * Map the Hyp-code called directly from the host
>>> */
>>> - err = create_hyp_mappings(__kvm_hyp_code_start, __kvm_hyp_code_end);
>>> + err = create_hyp_mappings(kvm_ksym_ref(__kvm_hyp_code_start),
>>> + kvm_ksym_ref(__kvm_hyp_code_end));
>>> if (err) {
>>> kvm_err("Cannot map world-switch code\n");
>>> goto out_free_mappings;
>>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
>>> index 7dace909d5cf..7c448b943e3a 100644
>>> --- a/arch/arm/kvm/mmu.c
>>> +++ b/arch/arm/kvm/mmu.c
>>> @@ -31,8 +31,6 @@
>>>
>>> #include "trace.h"
>>>
>>> -extern char __hyp_idmap_text_start[], __hyp_idmap_text_end[];
>>> -
>>> static pgd_t *boot_hyp_pgd;
>>> static pgd_t *hyp_pgd;
>>> static pgd_t *merged_hyp_pgd;
>>> @@ -63,7 +61,7 @@ static bool memslot_is_logging(struct kvm_memory_slot *memslot)
>>> */
>>> void kvm_flush_remote_tlbs(struct kvm *kvm)
>>> {
>>> - kvm_call_hyp(__kvm_tlb_flush_vmid, kvm);
>>> + kvm_call_hyp(kvm_ksym_ref(__kvm_tlb_flush_vmid), kvm);
>>
>> Any chance we could bury kvm_ksym_ref in kvm_call_hyp? It may make the
>> change more readable, but I have the feeling it would require an
>> intermediate #define...
>>
>
> Yes, we'd have to rename the actual kvm_call_hyp definition so we can
> wrap it in a macro
>
> And the call in __cpu_init_hyp_mode() would need to omit the macro,
> since it passes a pointer into the linear mapping, not a kernel
> symbol.
> So if you think that's ok, I'm happy to change that.

That'd be great, thanks.

M.
--
Jazz is not dead. It just smells funny...