Refinement of extended errors for mmap(2)

[mckusick]

Summary

Provide more precise error explanations for several of the mmap(2) EINVAL errors.

Test Plan

Run this program to verify that the updates are sensible:

#include <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/file.h>
#include <sys/mman.h>
#include <sys/stat.h>

int
main(int ac, char *av[])
{
	struct stat st;
	size_t len;
	off_t offset;
	int fd;
	char *mapaddr;

	if (ac != 2) {
		printf("Usage: %s file_to_map\n", av[0]);
		exit(1);
	}
	if ((fd = open(av[1], O_CREAT|O_RDWR, 0664)) < 0) {
		err(2, "open %s failed", av[1]);
	}
	if ((ftruncate(fd, 0x6400000)) < 0) {
		err(3, "truncate %s failed", av[1]);
	}
	if ((fstat(fd, &st)) < 0) {
		err(4, "stat %s failed", av[1]);
	}
	len = st.st_size;
	printf("%s size = %ld\n", av[1], len);
	offset = 0;
	if ((mapaddr = mmap(0, len, MAP_NOSYNC, PROT_READ, fd, offset)) == (char *)-1) {
		warn("mmap %s failed1", av[1]);
	}
	if ((mapaddr = mmap(0, 0, PROT_READ, MAP_ANON, fd, offset)) == (char *)-1) {
		warn("mmap %s failed2", av[1]);
	}
	if ((mapaddr = mmap(0, len, PROT_READ, MAP_STACK, fd, offset)) == (char *)-1) {
		warn("mmap %s failed3", av[1]);
	}
	if ((mapaddr = mmap(0, len, PROT_READ, MAP_RESERVED0080, fd, offset)) == (char *)-1) {
		warn("mmap %s failed4", av[1]);
	}
	if ((mapaddr = mmap(0, len, PROT_READ, MAP_EXCL, fd, offset)) == (char *)-1) {
		warn("mmap %s failed5", av[1]);
	}
	if ((mapaddr = mmap(0, len, PROT_READ, MAP_SHARED | MAP_PRIVATE, fd, offset)) == (char *)-1) {
		warn("mmap %s failed6", av[1]);
	}
	if ((mapaddr = mmap(0, len, PROT_READ, MAP_GUARD, fd, offset)) == (char *)-1) {
		warn("mmap %s failed7", av[1]);
	}
	if ((mapaddr = mmap(0, len, PROT_READ, MAP_ALIGNED(2), fd, offset)) == (char *)-1) {
		warn("mmap %s failed8", av[1]);
	}
	if ((mapaddr = mmap((char *)1, len, PROT_READ, MAP_FIXED, fd, offset)) == (char *)-1) {
		warn("mmap %s failed9", av[1]);
	}
	if ((mapaddr = mmap((void *)0x0000000080000000, len, PROT_READ, MAP_FIXED, fd, offset)) == (char *)-1) {
		warn("mmap %s failed10", av[1]);
	}
	if ((mapaddr = mmap((void *)0x0000000080000000, len, PROT_READ, MAP_32BIT|MAP_FIXED, fd, offset)) == (char *)-1) {
		warn("mmap %s failed11", av[1]);
	}
	printf("Mapped at 0x%lx\n", (unsigned long)mapaddr);
	close(fd);
	exit(0);
}

[kib]

sys/vm/vm_mmap.c

238–246

If doing that, I suggest not to repeat the tests. Split the main error check. as you did in the next chunk.

[mckusick]

Update per kib's suggestion.

[mckusick]

Update per your suggestion.

[kib]

sys/vm/vm_mmap.c

238–246

Isn't the new version changes the logic?

Before, if len == 0 and p_osrel >= something, we returned EINVAL.
Now it would only do that if fd != -1 or pos != 0.

I believe more splitting of the if() conditions is needed. And each case would get its own exterr.

[mckusick]

Valid complaint, but not sure what the error message should be for the third case.

sys/vm/vm_mmap.c

238–246

You are right that we did return EINVAL, but with an error that complained about two things that were not wrong. What should be the error message if (len == 0 && p->p_osrel >= P_OSREL_MAP_ANON)?

[kib]

sys/vm/vm_mmap.c

238–246

I propose "mapping with zero length".

[mckusick]

Further error message refinement.

[mckusick]

This time for sure!

[kib]

sys/vm/vm_mmap.c

277

This change should be a separate commit with the proper commit message.

330