linux/arch/x86/mm/maccess.c

// SPDX-License-Identifier: GPL-2.0-only

#include <linux/uaccess.h>
#include <linux/kernel.h>

#ifdef CONFIG_X86_64
static __always_inline u64 canonical_address(u64 vaddr, u8 vaddr_bits)
{
	return ((s64)vaddr << (64 - vaddr_bits)) >> (64 - vaddr_bits);
}

bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size)
{
	unsigned long vaddr = (unsigned long)unsafe_src;

	/*
	 * Range covering the highest possible canonical userspace address
	 * as well as non-canonical address range. For the canonical range
	 * we also need to include the userspace guard page.
	 */
	return vaddr >= TASK_SIZE_MAX + PAGE_SIZE &&
	       canonical_address(vaddr, boot_cpu_data.x86_virt_bits) == vaddr;
}
#else
bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size)
{
	return (unsigned long)unsafe_src >= TASK_SIZE_MAX;
}
#endif