linux-kernel - Re: [patch cr 2/4] [RFC] syscalls, x86: Add __NR

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Date:	Fri, 3 Feb 2012 08:46:56 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Kees Cook <keescook@...omium.org>, Tejun Heo <tj@...nel.org>,
	Andrew Vagin <avagin@...nvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Glauber Costa <glommer@...allels.com>,
	Matt Helsley <matthltc@...ibm.com>,
	Pekka Enberg <penberg@...nel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Vasiliy Kulikov <segoon@...nwall.com>, Valdis.Kletnieks@...edu
Subject: Re: [patch cr 2/4] [RFC] syscalls, x86: Add __NR_kcmp syscall v7


* Cyrill Gorcunov <gorcunov@...nvz.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
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