Re: [PATCH v3 3/9] KVM: arm64: Enable UBSAN_BOUNDS for the both the kernel and hyp/nVHE

[David Brazdil <dbrazdil@google.com>]

On Fri, Jan 15, 2021 at 05:18:24PM +0000, Elena Petrova 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 from the buffer is straightforward.
> 
> Signed-off-by: George Popescu <georgepope@google.com>
> Signed-off-by: Elena Petrova <lenaptr@google.com>
> ---
>  arch/arm64/include/asm/kvm_ubsan.h | 19 ++++++++++++++++++-
>  arch/arm64/kvm/hyp/nvhe/ubsan.c    | 14 ++++++++++++--
>  arch/arm64/kvm/kvm_ubsan_buffer.c  | 10 ++++++++++
>  3 files changed, 40 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_ubsan.h b/arch/arm64/include/asm/kvm_ubsan.h
> index fb32c7fd65d4..4f471acb88b0 100644
> --- a/arch/arm64/include/asm/kvm_ubsan.h
> +++ b/arch/arm64/include/asm/kvm_ubsan.h
> @@ -9,6 +9,23 @@
>  #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_OUT_OF_BOUNDS,
> +	} type;
> +	union {
> +		struct out_of_bounds_data out_of_bounds_data;
> +	};
> +	union {
> +		struct ubsan_values u_val;
> +	};

I don't see this second union having more members later in the series.
Remove it? Even the 'struct ubsan_values' seems redundant and we could just
have those three fields directly here.

>  };
> +
> +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 8a194fb1f6cf..55a8f6db8555 100644
> --- a/arch/arm64/kvm/hyp/nvhe/ubsan.c
> +++ b/arch/arm64/kvm/hyp/nvhe/ubsan.c
> @@ -13,7 +13,6 @@
>  #include <asm/kvm_ubsan.h>
>  #include <asm/kvm_debug_buffer.h>
>  #include <kvm/arm_pmu.h>
> -#include <ubsan.h>
>  
>  DEFINE_KVM_DEBUG_BUFFER(struct kvm_ubsan_info, kvm_ubsan_buffer,
>                  kvm_ubsan_buff_wr_ind, KVM_UBSAN_BUFFER_SIZE);
> @@ -44,7 +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;
> +	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 4a1959ba9f68..a1523f86be3c 100644
> --- a/arch/arm64/kvm/kvm_ubsan_buffer.c
> +++ b/arch/arm64/kvm/kvm_ubsan_buffer.c
> @@ -17,6 +17,15 @@
>  DECLARE_KVM_DEBUG_BUFFER(struct kvm_ubsan_info, kvm_ubsan_buffer,
>  		kvm_ubsan_buff_wr_ind, KVM_UBSAN_BUFFER_SIZE);
>  
> +void __kvm_check_ubsan_data(struct kvm_ubsan_info *slot)
> +{
> +	switch (slot->type) {
> +	case UBSAN_OUT_OF_BOUNDS:
> +		__ubsan_handle_out_of_bounds(&slot->out_of_bounds_data,
> +				slot->u_val.lval);
> +		break;
> +	}
> +}
>  
>  void iterate_kvm_ubsan_buffer(unsigned long left, unsigned long right)
>  {
> @@ -26,6 +35,7 @@ void iterate_kvm_ubsan_buffer(unsigned long left, unsigned long right)
>  	slot = (struct kvm_ubsan_info *) this_cpu_ptr_nvhe_sym(kvm_ubsan_buffer);
>  	for (i = left; i < right; ++i) {
>  		/* check ubsan data */
> +		__kvm_check_ubsan_data(slot + i);

Not sure why this is breaking out into another function. The code will not
be shared with any other user.

>  		slot[i].type = 0;

This invalidation is redundant. The buffer's cursor will be reset on next
hypercall, which will implicitly invalidate all entries.

>  	}
>  }
> -- 
> 2.30.0.296.g2bfb1c46d8-goog
> 
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