arch/x86/coco/virt_exception.c

// SPDX-License-Identifier: GPL-2.0-only
#include <linux/cpufeature.h>
#include <asm/insn.h>
#include <asm/insn-eval.h>
#include <asm/virt_exception.h>

struct ve_x86_ops ve_x86_ops;

int ve_handle_mmio(struct pt_regs *regs, struct ve_info *ve)
{
	unsigned long *reg, val, vaddr;
	char buffer[MAX_INSN_SIZE];
	enum insn_mmio_type mmio;
	struct insn insn = {};
	int size, extend_size;
	u8 extend_val = 0;

	/* Only in-kernel MMIO is supported */
	if (WARN_ON_ONCE(user_mode(regs)))
		return -EFAULT;

	if (copy_from_kernel_nofault(buffer, (void *)regs->ip, MAX_INSN_SIZE))
		return -EFAULT;

	if (insn_decode(&insn, buffer, MAX_INSN_SIZE, INSN_MODE_64))
		return -EINVAL;

	mmio = insn_decode_mmio(&insn, &size);
	if (WARN_ON_ONCE(mmio == INSN_MMIO_DECODE_FAILED))
		return -EINVAL;

	if (mmio != INSN_MMIO_WRITE_IMM && mmio != INSN_MMIO_MOVS) {
		reg = insn_get_modrm_reg_ptr(&insn, regs);
		if (!reg)
			return -EINVAL;
	}

	/*
	 * Reject EPT violation #VEs that split pages.
	 *
	 * MMIO accesses are supposed to be naturally aligned and therefore
	 * never cross page boundaries. Seeing split page accesses indicates
	 * a bug or a load_unaligned_zeropad() that stepped into an MMIO page.
	 *
	 * load_unaligned_zeropad() will recover using exception fixups.
	 */
	vaddr = (unsigned long)insn_get_addr_ref(&insn, regs);
	if (vaddr / PAGE_SIZE != (vaddr + size - 1) / PAGE_SIZE)
		return -EFAULT;

	/* Handle writes first */
	switch (mmio) {
	case INSN_MMIO_WRITE:
		memcpy(&val, reg, size);
		if (!ve_x86_ops.mmio_write(size, ve->gpa, val))
			return -EIO;
		return insn.length;
	case INSN_MMIO_WRITE_IMM:
		val = insn.immediate.value;
		if (!ve_x86_ops.mmio_write(size, ve->gpa, val))
			return -EIO;
		return insn.length;
	case INSN_MMIO_READ:
	case INSN_MMIO_READ_ZERO_EXTEND:
	case INSN_MMIO_READ_SIGN_EXTEND:
		/* Reads are handled below */
		break;
	case INSN_MMIO_MOVS:
	case INSN_MMIO_DECODE_FAILED:
		/*
		 * MMIO was accessed with an instruction that could not be
		 * decoded or handled properly. It was likely not using io.h
		 * helpers or accessed MMIO accidentally.
		 */
		return -EINVAL;
	default:
		WARN_ONCE(1, "Unknown insn_decode_mmio() decode value?");
		return -EINVAL;
	}

	/* Handle reads */
	if (!ve_x86_ops.mmio_read(size, ve->gpa, &val))
		return -EIO;

	switch (mmio) {
	case INSN_MMIO_READ:
		/* Zero-extend for 32-bit operation */
		extend_size = size == 4 ? sizeof(*reg) : 0;
		break;
	case INSN_MMIO_READ_ZERO_EXTEND:
		/* Zero extend based on operand size */
		extend_size = insn.opnd_bytes;
		break;
	case INSN_MMIO_READ_SIGN_EXTEND:
		/* Sign extend based on operand size */
		extend_size = insn.opnd_bytes;
		if (size == 1 && val & BIT(7))
			extend_val = 0xFF;
		else if (size > 1 && val & BIT(15))
			extend_val = 0xFF;
		break;
	default:
		/* All other cases has to be covered with the first switch() */
		WARN_ON_ONCE(1);
		return -EINVAL;
	}

	if (extend_size)
		memset(reg, extend_val, extend_size);
	memcpy(reg, &val, size);
	return insn.length;
}

bool handle_virt_exception(struct pt_regs *regs, struct ve_info *ve)
{
	if (ve_x86_ops.handle_virt_exception)
		return ve_x86_ops.handle_virt_exception(regs, ve);

	return false;
}

void get_ve_info(struct ve_info *ve)
{
	if (ve_x86_ops.get_ve_info)
		ve_x86_ops.get_ve_info(ve);
}