Re: [patch cr 2/4] [RFC] syscalls, x86: Add __NR_kcmp syscall v7

Ingo Molnar
2012-02-03T07:47:38Z

* Cyrill Gorcunov <gorcunov@openvz.org> wrote:

> +/* Comparision type */

> + * We don't expose real in-memory order of objects for security
> + * reasons, still the comparision results should be suitable for
> + * sorting. Thus, we obfuscate kernel pointers values (using random
> + * cookies obtaned at early boot stage) and compare the production
> + * instead.

> + * 0 - equal
> + * 1 - less than
> + * 2 - greater than
> + * 3 - not equal but ordering unavailable (reserved for future)

Broken spelling in each of those comment blocks. Are these
comments write-only?

> + /*
> + * Tasks are looked up in caller's
> + * PID namespace only.
> + */

Could be a single line.

> +
> + task1 = find_task_by_vpid(pid1);
> + if (!task1) {
> + rcu_read_unlock();
> + return -ESRCH;
> + }
> +
> + task2 = find_task_by_vpid(pid2);
> + if (!task2) {
> + put_task_struct(task1);
> + rcu_read_unlock();
> + return -ESRCH;
> + }

This is not the standard pattern of how we do error paths ...

> + /*
> + * Note for all cases but the KCMP_FILE we
> + * don't take any locks in a sake of speed.
> + */

Spelling.

> + get_random_bytes(&cookies[i][j],
> + sizeof(cookies[i][j]));

ugly line break.

> +late_initcall(kcmp_cookie_init);

any particular reason why this needs to be a late initcall?

> --- /dev/null
> +++ linux-2.6.git/tools/testing/selftests/kcmp/Makefile
> @@ -0,0 +1,35 @@
> +ifeq ($(strip $(V)),)
> + E = @echo
> + Q = @
> +else
> + E = @\#
> + Q =
> +endif
> +export E Q
> +
> +uname_M := $(shell uname -m 2>/dev/null || echo not)
> +ARCH ?= $(shell echo $(uname_M) | sed -e s/i.86/i386/)
> +ifeq ($(ARCH),i386)
> + ARCH := X86
> + CFLAGS := -DCONFIG_X86_32
> +endif
> +ifeq ($(ARCH),x86_64)
> + ARCH := X86
> + CFLAGS := -DCONFIG_X86_64
> +endif
> +
> +CFLAGS += -I../../../../arch/x86/include/generated/
> +CFLAGS += -I../../../../include/
> +
> +all:
> +ifeq ($(ARCH),X86)
> + $(E) " CC run_test"
> + $(Q) gcc $(CFLAGS) kcmp_test.c -o run_test
> +else
> + $(E) "Not an x86 target, can't build breakpoints selftests"
> +endif
> +
> +clean:
> + $(E) " CLEAN"
> + $(Q) rm -fr ./run_test
> + $(Q) rm -fr ./test-file

Needs buy-in from the kbuild guys.

> +#ifdef CONFIG_X86_64
> +#include <asm/unistd_64.h>
> +#else
> +#include <asm/unistd_32.h>
> +#endif

Why is asm/unistd.h not good?

> +static long sys_kcmp(int pid1, int pid2, int type, int fd1, int fd2)
> +{
> + return syscall(__NR_kcmp, (long)pid1, (long)pid2,
> + (long)type, (long)fd1, (long)fd2);
> +}

Why is a syscall that takes long arguments defined and called
with int and then cast over to long again?

> + int pid2 = getpid();
> + int ret;
> +
> + fd2 = open("test-file", O_RDWR, 0644);
> + if (fd2 < 0) {
> + perror("Can't open file");
> + exit(1);
> + }
> +
> + /* An example of output and arguments */
> + printf("pid1: %6d pid2: %6d FD: %2d FILES: %2d VM: %2d FS: %2d "
> + "SIGHAND: %2d IO: %2d SYSVSEM: %2d INV: %2d\n",

Visibly stray whitespaces.

> + /* This one should return same fd */
> + ret = sys_kcmp(pid1, pid2, KCMP_FILE, fd1, fd1);
> + if (ret) {
> + printf("FAIL: 0 expected but %d returned\n", ret);
> + ret = -1;
> + } else
> + printf("PASS: 0 returned as expected\n");
> + exit(ret);

this is main(), what's wrong with the standard pattern of return
ret?

I don't know whether this code is correct, but the high amount
of basic cleanliness problems makes me worry about that.

Thanks,

Ingo