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

Christoffer Dall
2016-01-05T14:56:01Z

On Tue, Jan 05, 2016 at 03:51:58PM +0100, Ard Biesheuvel wrote:
> On 5 January 2016 at 15:41, Christoffer Dall
> <christoffer.dall@linaro.org> wrote:
> > On Wed, Dec 30, 2015 at 04:26:04PM +0100, 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>
> >> ---
> >> 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 +427,7 @@ 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);
> >> }
> >>
> >> static void kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa)
> >> @@ -75,7 +73,7 @@ static void kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa)
> >> * anything there.
> >> */
> >> if (kvm)
> >> - kvm_call_hyp(__kvm_tlb_flush_vmid_ipa, kvm, ipa);
> >> + kvm_call_hyp(kvm_ksym_ref(__kvm_tlb_flush_vmid_ipa), kvm, ipa);
> >> }
> >>
> >> /*
> >> @@ -1647,9 +1645,9 @@ int kvm_mmu_init(void)
> >> {
> >> int err;
> >>
> >> - hyp_idmap_start = kvm_virt_to_phys(__hyp_idmap_text_start);
> >> - hyp_idmap_end = kvm_virt_to_phys(__hyp_idmap_text_end);
> >> - hyp_idmap_vector = kvm_virt_to_phys(__kvm_hyp_init);
> >> + hyp_idmap_start = kvm_virt_to_phys(&__hyp_idmap_text_start);
> >> + hyp_idmap_end = kvm_virt_to_phys(&__hyp_idmap_text_end);
> >> + hyp_idmap_vector = kvm_virt_to_phys(&__kvm_hyp_init);
> >>
> >> /*
> >> * We rely on the linker script to ensure at build time that the HYP
> >> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> >> index 5e377101f919..830402f847e0 100644
> >> --- a/arch/arm64/include/asm/kvm_asm.h
> >> +++ b/arch/arm64/include/asm/kvm_asm.h
> >> @@ -105,24 +105,27 @@
> >> #ifndef __ASSEMBLY__
> >> struct kvm;
> >> struct kvm_vcpu;
> >> +struct kvm_ksym;
> >>
> >> extern char __kvm_hyp_init[];
> >> extern char __kvm_hyp_init_end[];
> >>
> >> -extern char __kvm_hyp_vector[];
> >> +extern struct kvm_ksym __kvm_hyp_vector;
> >>
> >> -#define __kvm_hyp_code_start __hyp_text_start
> >> -#define __kvm_hyp_code_end __hyp_text_end
> >> +extern struct kvm_ksym __kvm_hyp_code_start;
> >> +extern struct kvm_ksym __kvm_hyp_code_end;
> >>
> >> -extern void __kvm_flush_vm_context(void);
> >> -extern void __kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa);
> >> -extern void __kvm_tlb_flush_vmid(struct kvm *kvm);
> >> +extern struct kvm_ksym __kvm_flush_vm_context;
> >> +extern struct kvm_ksym __kvm_tlb_flush_vmid_ipa;
> >> +extern struct kvm_ksym __kvm_tlb_flush_vmid;
> >>
> >> -extern int __kvm_vcpu_run(struct kvm_vcpu *vcpu);
> >> +extern struct kvm_ksym __kvm_vcpu_run;
> >>
> >> -extern u64 __vgic_v3_get_ich_vtr_el2(void);
> >> +extern struct kvm_ksym __hyp_idmap_text_start, __hyp_idmap_text_end;
> >>
> >> -extern u32 __kvm_get_mdcr_el2(void);
> >> +extern struct kvm_ksym __vgic_v3_get_ich_vtr_el2;
> >> +
> >> +extern struct kvm_ksym __kvm_get_mdcr_el2;
> >>
> >> #endif
> >>
> >> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> >> index 61505676d085..0899026a2821 100644
> >> --- a/arch/arm64/include/asm/kvm_mmu.h
> >> +++ b/arch/arm64/include/asm/kvm_mmu.h
> >> @@ -73,6 +73,8 @@
> >>
> >> #define KERN_TO_HYP(kva) ((unsigned long)kva - PAGE_OFFSET + HYP_PAGE_OFFSET)
> >>
> >> +#define kvm_ksym_ref(sym) ((void *)&sym - KIMAGE_VADDR + PAGE_OFFSET)
> >> +
> >> /*
> >> * We currently only support a 40bit IPA.
> >> */
> >> diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
> >> index 7a5df5252dd7..215ad4649dd7 100644
> >> --- a/arch/arm64/include/asm/virt.h
> >> +++ b/arch/arm64/include/asm/virt.h
> >> @@ -50,10 +50,6 @@ static inline bool is_hyp_mode_mismatched(void)
> >> return __boot_cpu_mode[0] != __boot_cpu_mode[1];
> >> }
> >>
> >> -/* The section containing the hypervisor text */
> >> -extern char __hyp_text_start[];
> >> -extern char __hyp_text_end[];
> >> -
> >> #endif /* __ASSEMBLY__ */
> >>
> >> #endif /* ! __ASM__VIRT_H */
> >> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> >> index 363c2f529951..f935f082188d 100644
> >> --- a/arch/arm64/kernel/vmlinux.lds.S
> >> +++ b/arch/arm64/kernel/vmlinux.lds.S
> >> @@ -35,9 +35,9 @@ jiffies = jiffies_64;
> >> VMLINUX_SYMBOL(__hyp_idmap_text_start) = .; \
> >> *(.hyp.idmap.text) \
> >> VMLINUX_SYMBOL(__hyp_idmap_text_end) = .; \
> >> - VMLINUX_SYMBOL(__hyp_text_start) = .; \
> >> + VMLINUX_SYMBOL(__kvm_hyp_code_start) = .; \
> >> *(.hyp.text) \
> >> - VMLINUX_SYMBOL(__hyp_text_end) = .;
> >> + VMLINUX_SYMBOL(__kvm_hyp_code_end) = .;
> >
> > why this rename?
> >
>
> I already got rid of it based on Marc's feedback. The only reason was
> to align between ARM and arm64, but he is already doing the same in
> the opposite direction

ah, now I understand what Marc was referring to in his comment, thanks.

-Christoffer