KVM: arm64: Add a buffer that can pass UBSan data from hyp/nVHE to ke…

…rnel

Share a buffer between the kernel and the hyp/nVHE code by using the
macros from kvm_debug_buffer.h.
The hyp/nVHE code requires a write index which counts how many elements
have been writtens inside the buffer and the kernel requires a read
index which counts how many elements have been read from the buffer.
The write index and the buffer are shared with the kernel in read-only.

The kvm_debug_buffer_ind returns the reading and writing points of the
circular buffer and updates the reading index.

Data collected from UBSan handlers inside hyp/nVHE is stored in the
kvm_ubsan_buffer.
This buffer stores only UBSan data because it should not be preoccupied
by other mechanisms data structures and functionalities.

Also, for the moment the buffer is mapped inside .bss, where both the kernel
and the hyp/nVHE code have Read/Write rights, but in the future this will change
and the kernel will not be able to acess hyp/nVHE's .bss. At that point the buffer
will only need to be mapped in order for this patch to work.

Change-Id: I696409db1de629b082abfe4c7f6bf066f12b539f
Signed-off-by: Elena Petrova <lenaptr@google.com>

arch/arm64/include/asm/assembler.h

@@ -258,6 +258,17 @@ alternative_endif
 	ldr	\dst, [\dst, \tmp]
 	.endm
 
+	/*
+         * @sym: The name of the per-cpu variable
+         * @reg: value to store
+         * @tmp1: scratch register
+         * @tmp2: scratch register
+         */
+        .macro str_this_cpu sym, reg, tmp1, tmp2
+        adr_this_cpu \tmp1, \sym, \tmp2
+        str \reg, [\tmp1]
+        .endm
+
 /*
  * vma_vm_mm - get mm pointer from vma pointer (vma->vm_mm)
  */

arch/arm64/include/asm/kvm_debug_buffer.h

@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2020 Google LLC
+ * Author: George Popescu <georgepope@google.com>
+ */
+
+#include <linux/percpu-defs.h>
+
+
+#define KVM_DEBUG_BUFFER_SIZE 1000
+
+#ifdef __KVM_NVHE_HYPERVISOR__
+#define DEFINE_KVM_DEBUG_BUFFER(type_name, buffer_name, write_ind, size)\
+	DEFINE_PER_CPU(type_name, buffer_name)[size];			\
+	DEFINE_PER_CPU(unsigned long, write_ind) = 0;
+
+#define DECLARE_KVM_DEBUG_BUFFER(type_name, buffer_name, write_ind, size)\
+	DECLARE_PER_CPU(type_name, buffer_name)[size];			\
+	DECLARE_PER_CPU(unsigned long, write_ind);
+#else
+#define DECLARE_KVM_DEBUG_BUFFER(type_name, buffer_name, write_ind, size)\
+	DECLARE_KVM_NVHE_PER_CPU(type_name, buffer_name)[size]; 	\
+        DECLARE_KVM_NVHE_PER_CPU(unsigned long, write_ind);
+#endif //__KVM_NVHE_HYPERVISOR__
+
+#ifdef __ASSEMBLY__
+#include <asm/assembler.h>
+
+.macro clear_buffer tmp1, tmp2, tmp3
+        mov \tmp1, 0
+#ifdef CONFIG_UBSAN
+        str_this_cpu kvm_ubsan_buff_wr_ind, \tmp1, \tmp2, \tmp3
+#endif //CONFIG_UBSAN
+.endm
+
+#endif

arch/arm64/include/asm/kvm_host.h

@@ -569,14 +569,20 @@ int kvm_test_age_hva(struct kvm *kvm, unsigned long hva);
 void kvm_arm_halt_guest(struct kvm *kvm);
 void kvm_arm_resume_guest(struct kvm *kvm);
 
+
+#ifdef CONFIG_UBSAN
+extern void __kvm_check_ubsan_buffer(void);
+#else
+static inline void __kvm_check_ubsan_buffer(void) {}
+#endif /* CONFIG_UBSAN */
 #define kvm_call_hyp_nvhe(f, ...)						\
 	({								\
 		struct arm_smccc_res res;				\
 									\
 		arm_smccc_1_1_hvc(KVM_HOST_SMCCC_FUNC(f),		\
 				  ##__VA_ARGS__, &res);			\
 		WARN_ON(res.a0 != SMCCC_RET_SUCCESS);			\
-									\
+		__kvm_check_ubsan_buffer();				\
 		res.a1;							\
 	})
 

arch/arm64/include/asm/kvm_ubsan.h

@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2020 Google LLC
+ * Author: George Popescu <georgepope@google.com>
+ */
+
+#include <ubsan.h>
+
+#define UBSAN_MAX_TYPE 6
+#define KVM_UBSAN_BUFFER_SIZE 1000
+
+struct kvm_ubsan_info {
+	int type;
+};

arch/arm64/kvm/Makefile

@@ -4,6 +4,7 @@
 #
 
 ccflags-y += -I $(srctree)/$(src)
+CFLAGS_kvm_ubsan_buffer.o += -I $(srctree)/lib/
 
 KVM=../../../virt/kvm
 
@@ -24,4 +25,5 @@ kvm-y := $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o $(KVM)/eventfd.o \
 	 vgic/vgic-mmio-v3.o vgic/vgic-kvm-device.o \
 	 vgic/vgic-its.o vgic/vgic-debug.o
 
+kvm-$(CONFIG_UBSAN) += kvm_ubsan_buffer.o
 kvm-$(CONFIG_KVM_ARM_PMU)  += pmu-emul.o

arch/arm64/kvm/arm.c

@@ -1780,6 +1780,15 @@ static int init_hyp_mode(void)
 			goto out_err;
 		}
 	}
+#ifdef CONFIG_UBSAN
+	/* required by ubsan to access the handlers structures fields */
+	err = create_hyp_mappings(kvm_ksym_ref(_data),
+				  kvm_ksym_ref(__end_once), PAGE_HYP_RO);
+	if (err) {
+		kvm_err("Cannot map data section\n");
+		goto out_err;
+	}
+#endif
 
 	/*
 	 * Map Hyp percpu pages

arch/arm64/kvm/hyp/nvhe/host.S

@@ -8,6 +8,7 @@
 
 #include <asm/assembler.h>
 #include <asm/kvm_asm.h>
+#include <asm/kvm_debug_buffer.h>
 #include <asm/kvm_mmu.h>
 
 	.text
@@ -34,6 +35,9 @@ SYM_FUNC_START(__host_exit)
 	/* Store the host regs x18-x29, lr */
 	save_callee_saved_regs x0
 
+	/* when entering the host clear the buffers */
+   	clear_buffer    x4, x5, x6  
+
 	/* Save the host context pointer in x29 across the function call */
 	mov	x29, x0
 	bl	handle_trap

arch/arm64/kvm/hyp/nvhe/ubsan.c

@@ -3,10 +3,33 @@
  * Copyright 2020 Google LLC
  * Author: George Popescu <georgepope@google.com>
  */
+#include <linux/bitops.h>
 #include <linux/ctype.h>
 #include <linux/types.h>
+#include <linux/percpu-defs.h>
+#include <linux/kvm_host.h>
+#include <asm/kvm_arm.h>
+#include <asm/kvm_asm.h>
+#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);
+
+static inline struct kvm_ubsan_info *kvm_ubsan_buffer_next_slot(void)
+{
+	struct kvm_ubsan_info *res = NULL;
+	unsigned long write_ind = __this_cpu_read(kvm_ubsan_buff_wr_ind);
+	if (write_ind < KVM_UBSAN_BUFFER_SIZE) {
+		res = this_cpu_ptr(&kvm_ubsan_buffer[write_ind]);
+		++write_ind;
+		__this_cpu_write(kvm_ubsan_buff_wr_ind, write_ind);
+	}
+	return res;
+}
+
 void __ubsan_handle_add_overflow(void *_data, void *lhs, void *rhs) {}
 
 void __ubsan_handle_sub_overflow(void *_data, void *lhs, void *rhs) {}

arch/arm64/kvm/kvm_ubsan_buffer.c

@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2020 Google LLC
+ * Author: George Popescu <georgepope@google.com>
+ */
+
+#include <linux/ctype.h>
+#include <linux/types.h>
+#include <asm/kvm_debug_buffer.h>
+#include <asm/kvm_arm.h>
+#include <asm/kvm_asm.h>
+#include <kvm/arm_pmu.h>
+
+#include <ubsan.h>
+#include <asm/kvm_ubsan.h>
+
+DECLARE_KVM_DEBUG_BUFFER(struct kvm_ubsan_info, kvm_ubsan_buffer,
+		kvm_ubsan_buff_wr_ind, KVM_UBSAN_BUFFER_SIZE);
+
+
+void iterate_kvm_ubsan_buffer(unsigned long left, unsigned long right)
+{
+	unsigned long i;
+	struct kvm_ubsan_info *slot;
+
+	slot = (struct kvm_ubsan_info *) this_cpu_ptr_nvhe_sym(kvm_ubsan_buffer);
+	for (i = left; i < right; ++i) {
+		/* check ubsan data */
+		slot[i].type = 0;
+	}
+}
+
+void __kvm_check_ubsan_buffer(void)
+{
+	unsigned long *write_ind;
+
+	write_ind = (unsigned long *) this_cpu_ptr_nvhe_sym(kvm_ubsan_buff_wr_ind);
+	iterate_kvm_ubsan_buffer(0, *write_ind);
+}
+