Re: [PATCH 07/14] KVM: arm64: Enable UBSAN_BOUNDS for the both the kernel and hyp/nVHE

[Andrew Scull <ascull@google.com>]

On Mon, Sep 14, 2020 at 05:27:43PM +0000, George-Aurelian Popescu wrote:
> From: George Popescu <georgepope@google.com>
> 
> If an out of bounds happens inside the hyp/nVHE code, the
> ubsan_out_of_bounds handler stores the logging data inside the
> kvm_ubsan_buffer. The one responsible for printing is the kernel
> ubsan_out_of_bounds handler. The process of decapsulating the data happens
> in kvm_ubsan_buffer.c.
> 
> The struct kvm_ubsan_info contains three main components:
> -enum type, which is used to identify which handler to call from the
> kernel.
> -struct ubsan_values, which stores the operands involved during the
> undefined behaviours, which can be one, two or zero, depending on what
> undefiend behaviour is reported. As an example for: out_of_bounds there
> is only one operand (the index).
> 
> Accessing a slot with no type should do nothing. Each slot is marked
> with the UBSAN_NONE tag after it's first usage.
> 
> Signed-off-by: George Popescu <georgepope@google.com>
> ---
>  arch/arm64/include/asm/kvm_ubsan.h | 19 ++++++++++++++++++-
>  arch/arm64/kvm/hyp/nvhe/ubsan.c    | 13 ++++++++++++-
>  arch/arm64/kvm/kvm_ubsan_buffer.c  | 13 ++++++++++++-
>  3 files changed, 42 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_ubsan.h b/arch/arm64/include/asm/kvm_ubsan.h
> index af607a796376..575881e0bd5f 100644
> --- a/arch/arm64/include/asm/kvm_ubsan.h
> +++ b/arch/arm64/include/asm/kvm_ubsan.h
> @@ -11,7 +11,24 @@
>  #define UBSAN_MAX_TYPE 6
>  #define KVM_UBSAN_BUFFER_SIZE 1000
>  
> +struct ubsan_values {
> +	void *lval;
> +	void *rval;
> +	char op;
> +};
> +
>  struct kvm_ubsan_info {
> -	int type;
> +	enum {
> +		UBSAN_NONE,
> +		UBSAN_OUT_OF_BOUNDS
> +	} type;
> +	union {
> +		struct out_of_bounds_data out_of_bounds_data;
> +	};
> +	union {
> +		struct ubsan_values u_val;
> +	};
>  };
>  #endif
> +
> +void __ubsan_handle_out_of_bounds(void *_data, void *index);
> diff --git a/arch/arm64/kvm/hyp/nvhe/ubsan.c b/arch/arm64/kvm/hyp/nvhe/ubsan.c
> index a43c9646e1e8..b2d3404f6215 100644
> --- a/arch/arm64/kvm/hyp/nvhe/ubsan.c
> +++ b/arch/arm64/kvm/hyp/nvhe/ubsan.c
> @@ -43,7 +43,18 @@ void __ubsan_handle_type_mismatch(struct type_mismatch_data *data, void *ptr) {}
>  
>  void __ubsan_handle_type_mismatch_v1(void *_data, void *ptr) {}
>  
> -void __ubsan_handle_out_of_bounds(void *_data, void *index) {}
> +void __ubsan_handle_out_of_bounds(void *_data, void *index)
> +{
> +	struct kvm_ubsan_info *slot = NULL;
> +	struct out_of_bounds_data *data = _data;
> +
> +	slot = kvm_ubsan_buffer_next_slot();
> +	if (slot) {
> +		slot->type = UBSAN_OUT_OF_BOUNDS;
> +		slot->out_of_bounds_data = *data;
> +		slot->u_val.lval = index;
> +	}
> +}
>  
>  void __ubsan_handle_shift_out_of_bounds(void *_data, void *lhs, void *rhs) {}
>  
> diff --git a/arch/arm64/kvm/kvm_ubsan_buffer.c b/arch/arm64/kvm/kvm_ubsan_buffer.c
> index 28dcf19b5706..ce796bdd027e 100644
> --- a/arch/arm64/kvm/kvm_ubsan_buffer.c
> +++ b/arch/arm64/kvm/kvm_ubsan_buffer.c
> @@ -16,6 +16,17 @@
>  
>  DECLARE_KVM_DEBUG_BUFFER(struct kvm_ubsan_info, kvm_ubsan_buff, KVM_UBSAN_BUFFER_SIZE);
>  
> +void __kvm_check_ubsan_data(struct kvm_ubsan_info *slot)
> +{
> +	switch (slot->type) {
> +	case UBSAN_NONE:
> +		break;
> +	case UBSAN_OUT_OF_BOUNDS:
> +		__ubsan_handle_out_of_bounds(&slot->out_of_bounds_data,
> +				slot->u_val.lval);
> +		break;
> +	}
> +}
>  
>  void __kvm_check_ubsan_buffer(void)
>  {
> @@ -25,7 +36,7 @@ void __kvm_check_ubsan_buffer(void)
>  
>  	init_kvm_debug_buffer(kvm_ubsan_buff, struct kvm_ubsan_info, slot, write_ind);
>  	for_each_kvm_debug_buffer_slot(slot, write_ind, it) {
> -		/* check ubsan data */
> +		__kvm_check_ubsan_data(slot);
>  		slot->type = 0;

0's called UBSAN_NONE now

>  	}
>  }
> -- 
> 2.28.0.618.gf4bc123cb7-goog
>