C pointer check at runtime

ptrcheck.asm

# Assembly code of:
#     clang -arch x86_64 -masm=intel -S -Wall -O3 -o - ptrcheck.c
#
	.text
	.intel_syntax noprefix
	.file	"ptrcheck.c"
	.globl	isValidPointer                  # -- Begin function isValidPointer
	.p2align	4, 0x90
	.type	isValidPointer,@function
isValidPointer:                         # @isValidPointer
	.cfi_startproc
# %bb.0:
	push	rbp
	.cfi_def_cfa_offset 16
	.cfi_offset rbp, -16
	mov	rbp, rsp
	.cfi_def_cfa_register rbp
	push	rbx
	push	rax
	.cfi_offset rbx, -24
	test	rdi, rdi
	je	.LBB0_3
# %bb.1:
	mov	rbx, rdi
	lea	rdi, [rbp - 16]
	call	pipe
	test	eax, eax
	je	.LBB0_4
.LBB0_3:
	xor	ebx, ebx
	jmp	.LBB0_7
.LBB0_4:
	mov	edi, dword ptr [rbp - 12]
	mov	edx, 8
	mov	rsi, rbx
	call	write
	mov	rbx, rax
	test	rax, rax
	jns	.LBB0_6
# %bb.5:
	call	__error
.LBB0_6:
	test	rbx, rbx
	setns	bl
	mov	edi, dword ptr [rbp - 16]
	call	close
	mov	edi, dword ptr [rbp - 12]
	call	close
.LBB0_7:
	mov	eax, ebx
	add	rsp, 8
	pop	rbx
	pop	rbp
	.cfi_def_cfa rsp, 8
	ret
.Lfunc_end0:
	.size	isValidPointer, .Lfunc_end0-isValidPointer
	.cfi_endproc
                                        # -- End function
	.ident	"FreeBSD clang version 14.0.5 (https://github.com/llvm/llvm-project.git llvmorg-14.0.5-0-gc12386ae247c)"
	.section	".note.GNU-stack","",@progbits
	.addrsig

ptrcheck.c

#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdbool.h>
#include <unistd.h>

bool isValidPointer(void * ptr) {
    bool ret = false;
    int fd[2];
    if (NULL == ptr) {
        return ret;
    }
    if (pipe(fd) == 0) {
        if (write(fd[1], ptr, sizeof(ptr)) < 0) {
            if (errno == EFAULT) {
//                 strerror(errno);  // this is what we expected to happen
            }
//             strerror(errno);  // to see what happened...
        } else {
            ret = true;
        }
        close(fd[0]);   // close filedescriptors
        close(fd[1]);   //
    }
    return ret;
}

ptrcheck.h

#ifndef __PTRCHECK__H__
#define __PTRCHECK__H__
#include <stdbool.h>
bool isValidPointer(void *ptr);
#endif  //!__PTRCHECK__H__

test.c

#include <stdio.h>
#include <stdlib.h>
#include "ptrcheck.h"

int main(int argc, char** argv) {
    void *ptr = NULL;
    int a = 0;
    int* pa = &a;
    int* ip = 0x08219431a2;
    printf("    void* ptr: %s [%p]\n", isValidPointer(ptr) ? "Valid" : "Invalid", ptr);
    printf("       int* a: %s [%p]\n", isValidPointer(pa) ? "Valid" : "Invalid", pa);
    printf("      int* ip: %s [%p]\n", isValidPointer(ip) ? "Valid" : "Invalid", ip);
    printf("   void** ptr: %s [%p]\n", isValidPointer(&ptr) ? "Valid" : "Invalid", &ptr);
    return  EXIT_SUCCESS;
}

How to check is your C pointer is valid in your process's address space?
After a great review of Jacob Sorber.

After a test run, the output should be: "Invalid, Valid, Invalid, Valid" in this order.

However as it used to be, better to avoid bad pointers in your code, than utilize extra resources to check their validity.