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

From: [email-masked] (Marc Zyngier)
Date: Mon, 04 Jan 2016 10:08:02 +0000

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 <[email-masked]>

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 +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);

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...

>  }
>  
>  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);

Why don't you need to use kvm_ksym_ref here? Is the idmap treated
differently?

>  
>  	/*
>  	 * 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;

And that's it? Never actually defined? That's cunning! ;-)

>  
>  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) = .;

I have a couple of patches going in the exact opposite direction (making
arm more similar to arm64):

http://git.kernel.org/cgit/linux/kernel/git/maz/arm-platforms.git/commit/?h=kvm-arm/wsinc&id=94a3d4d4ff1d8ad59f9150dfa9fdd1685ab03950
http://git.kernel.org/cgit/linux/kernel/git/maz/arm-platforms.git/commit/?h=kvm-arm/wsinc&id=44aec57b62dca67cf91f425e3707f257b9bbeb18

As at least the first patch is required to convert the 32bit HYP code to
C, I'd rather not change this in the 64bit code.

>  
>  #define IDMAP_TEXT					\
>  	. = ALIGN(SZ_4K);				\
> diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
> index 47e5f0feaee8..99e5a403af4e 100644
> --- a/arch/arm64/kvm/debug.c
> +++ b/arch/arm64/kvm/debug.c
> @@ -24,6 +24,7 @@
>  #include <asm/kvm_asm.h>
>  #include <asm/kvm_arm.h>
>  #include <asm/kvm_emulate.h>
> +#include <asm/kvm_mmu.h>
>  
>  #include "trace.h"
>  
> @@ -72,7 +73,8 @@ static void restore_guest_debug_regs(struct kvm_vcpu *vcpu)
>  
>  void kvm_arm_init_debug(void)
>  {
> -	__this_cpu_write(mdcr_el2, kvm_call_hyp(__kvm_get_mdcr_el2));
> +	__this_cpu_write(mdcr_el2,
> +			 kvm_call_hyp(kvm_ksym_ref(__kvm_get_mdcr_el2)));
>  }
>  
>  /**
> diff --git a/virt/kvm/arm/vgic-v3.c b/virt/kvm/arm/vgic-v3.c
> index 487d6357b7e7..58f5a6521307 100644
> --- a/virt/kvm/arm/vgic-v3.c
> +++ b/virt/kvm/arm/vgic-v3.c
> @@ -247,7 +247,7 @@ int vgic_v3_probe(struct device_node *vgic_node,
>  		goto out;
>  	}
>  
> -	ich_vtr_el2 = kvm_call_hyp(__vgic_v3_get_ich_vtr_el2);
> +	ich_vtr_el2 = kvm_call_hyp(kvm_ksym_ref(__vgic_v3_get_ich_vtr_el2));
>  
>  	/*
>  	 * The ListRegs field is 5 bits, but there is a architectural
> 

Thanks,

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