[PATCH v3 8/9] KVM: arm64: Detect arithmetic overflow is inside hyp/nVHE.

[Elena Petrova]

From: George Popescu <georgepope at google.com>

Whenever an arithmetic overflow: addition, substraction, multiplication,
division or negating happens inside the hyp/nVHE code,
an __ubsan_handle_*_overflow is called.

All the overflow handlers are sharing the same structure called
overflow_data.

Signed-off-by: George Popescu <georgepope at google.com>
Signed-off-by: Elena Petrova <lenaptr at google.com>
---
 arch/arm64/include/asm/kvm_ubsan.h | 10 ++++++--
 arch/arm64/kvm/hyp/nvhe/ubsan.c    | 40 ++++++++++++++++++++++++++----
 arch/arm64/kvm/kvm_ubsan_buffer.c  | 20 ++++++++++++++-
 3 files changed, 62 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_ubsan.h b/arch/arm64/include/asm/kvm_ubsan.h
index 93c1b695097a..da4a3b4e28e0 100644
--- a/arch/arm64/include/asm/kvm_ubsan.h
+++ b/arch/arm64/include/asm/kvm_ubsan.h
@@ -22,7 +22,8 @@ struct kvm_ubsan_info {
 		UBSAN_UNREACHABLE_DATA,
 		UBSAN_SHIFT_OUT_OF_BOUNDS,
 		UBSAN_INVALID_DATA,
-		UBSAN_TYPE_MISMATCH
+		UBSAN_TYPE_MISMATCH,
+		UBSAN_OVERFLOW_DATA
 	} type;
 	union {
 		struct out_of_bounds_data out_of_bounds_data;
@@ -30,6 +31,7 @@ struct kvm_ubsan_info {
 		struct shift_out_of_bounds_data shift_out_of_bounds_data;
 		struct invalid_value_data invalid_value_data;
 		struct type_mismatch_data type_mismatch_data;
+		struct overflow_data overflow_data;
 	};
 	union {
 		struct ubsan_values u_val;
@@ -41,4 +43,8 @@ void __ubsan_handle_builtin_unreachable(void *_data);
 void __ubsan_handle_shift_out_of_bounds(void *_data, void *lhs, void *rhs);
 void __ubsan_handle_load_invalid_value(void *_data, void *val);
 void __ubsan_handle_type_mismatch(struct type_mismatch_data  *_data, void *ptr);
-
+void __ubsan_handle_add_overflow(void *data, void *lhs, void *rhs);
+void __ubsan_handle_sub_overflow(void *data, void *lhs, void *rhs);
+void __ubsan_handle_mul_overflow(void *data, void *lhs, void *rhs);
+void __ubsan_handle_negate_overflow(void *_data, void *old_val);
+void __ubsan_handle_divrem_overflow(void *_data, void *lhs, void *rhs);
diff --git a/arch/arm64/kvm/hyp/nvhe/ubsan.c b/arch/arm64/kvm/hyp/nvhe/ubsan.c
index a9f72d4bcab7..f16842ff7316 100644
--- a/arch/arm64/kvm/hyp/nvhe/ubsan.c
+++ b/arch/arm64/kvm/hyp/nvhe/ubsan.c
@@ -47,15 +47,45 @@ static void write_type_mismatch_data(struct type_mismatch_data_common *data, voi
 	}
 }
 
-void __ubsan_handle_add_overflow(void *_data, void *lhs, void *rhs) {}
+static void write_overflow_data(struct overflow_data *data, void *lval, void *rval, char op)
+{
+	struct kvm_ubsan_info *slot = kvm_ubsan_buffer_next_slot();
+
+	if (slot) {
+		slot->type = UBSAN_OVERFLOW_DATA;
+		slot->overflow_data = *data;
+		slot->u_val.op = op;
+		slot->u_val.lval = lval;
+		if (op != '!')
+			slot->u_val.rval = rval;
+	}
+}
+
+void __ubsan_handle_add_overflow(void *_data, void *lhs, void *rhs)
+{
+	write_overflow_data(_data, lhs, rhs, '+');
+}
 
-void __ubsan_handle_sub_overflow(void *_data, void *lhs, void *rhs) {}
+void __ubsan_handle_sub_overflow(void *_data, void *lhs, void *rhs)
+{
+	write_overflow_data(_data, lhs, rhs, '-');
+}
 
-void __ubsan_handle_mul_overflow(void *_data, void *lhs, void *rhs) {}
+void __ubsan_handle_mul_overflow(void *_data, void *lhs, void *rhs)
+{
+	write_overflow_data(_data, lhs, rhs, '*');
+}
 
-void __ubsan_handle_negate_overflow(void *_data, void *old_val) {}
+void __ubsan_handle_negate_overflow(void *_data, void *old_val)
+{
+	write_overflow_data(_data, old_val, NULL, '!');
+}
+
+void __ubsan_handle_divrem_overflow(void *_data, void *lhs, void *rhs)
+{
+	write_overflow_data(_data, lhs, rhs, '/');
+}
 
-void __ubsan_handle_divrem_overflow(void *_data, void *lhs, void *rhs) {}
 
 void __ubsan_handle_type_mismatch(struct type_mismatch_data *data, void *ptr)
 {
diff --git a/arch/arm64/kvm/kvm_ubsan_buffer.c b/arch/arm64/kvm/kvm_ubsan_buffer.c
index b7823dedf8b1..2c7060cbb48b 100644
--- a/arch/arm64/kvm/kvm_ubsan_buffer.c
+++ b/arch/arm64/kvm/kvm_ubsan_buffer.c
@@ -39,7 +39,25 @@ void __kvm_check_ubsan_data(struct kvm_ubsan_info *slot)
 		__ubsan_handle_type_mismatch(&slot->type_mismatch_data,
 				slot->u_val.lval);
 		break;
-    	}
+	case UBSAN_OVERFLOW_DATA:
+		if (slot->u_val.op == '/') {
+			__ubsan_handle_divrem_overflow(&slot->overflow_data,
+					slot->u_val.lval, slot->u_val.rval);
+		} else if (slot->u_val.op == '!') {
+			__ubsan_handle_negate_overflow(&slot->overflow_data,
+					slot->u_val.lval);
+		} else if (slot->u_val.op == '+') {
+			__ubsan_handle_add_overflow(&slot->overflow_data,
+					slot->u_val.lval, slot->u_val.rval);
+		} else if (slot->u_val.op == '-') {
+			__ubsan_handle_sub_overflow(&slot->overflow_data,
+					slot->u_val.lval, slot->u_val.rval);
+		} else if (slot->u_val.op == '*') {
+			__ubsan_handle_mul_overflow(&slot->overflow_data,
+					slot->u_val.lval, slot->u_val.rval);
+		}
+		break;
+    }
 }
 
 void iterate_kvm_ubsan_buffer(unsigned long left, unsigned long right)
-- 
2.30.0.296.g2bfb1c46d8-goog