From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
KOSAKI Motohiro <kosaki.motohiro@gmail.com>,
"H. Peter Anvin" <hpa@zytor.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
linux-kernel@vger.kernel.org,
Pavel Emelyanov <xemul@parallels.com>,
Serge Hallyn <serge.hallyn@canonical.com>,
Kees Cook <keescook@chromium.org>, Tejun Heo <tj@kernel.org>,
Andrew Vagin <avagin@openvz.org>,
Alexey Dobriyan <adobriyan@gmail.com>,
Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>,
Glauber Costa <glommer@parallels.com>,
Andi Kleen <andi@firstfloor.org>,
Matt Helsley <matthltc@us.ibm.com>,
Pekka Enberg <penberg@kernel.org>,
Eric Dumazet <eric.dumazet@gmail.com>,
Vasiliy Kulikov <segoon@openwall.com>,
Valdis.Kletnieks@vt.edu
Subject: Re: [patch 2/4] [RFC] syscalls, x86: Add __NR_kcmp syscall v4
Date: Wed, 25 Jan 2012 01:46:30 +0400 [thread overview]
Message-ID: <20120124214630.GF2546@moon> (raw)
In-Reply-To: <20120124132222.d78bc0d4.akpm@linux-foundation.org>
On Tue, Jan 24, 2012 at 01:22:22PM -0800, Andrew Morton wrote:
>
> PIDs are not unique. One wonders what happens in this syscall if the
> same pid appears in two namespaces.
>
> <reads the code>
>
> Seems that it performs lookups only in the caller's PID namespace.
> Maybe this is appropriate but it should be described and justified in
> the changelog and in code comments, please. And in the forthcoming
> manpage ;)
>
Yes, caller's namespace was used intentionally, will add comments (manpage
makes me shiver).
> > At moment only x86 is supported.
>
> Presumably you have a test app. Please let's include that app in
> tools/testing/selftests/ for arch maintainers and others to use and
> maintain.
ok
> > +static unsigned long cookies[KCMP_TYPES][2] __read_mostly;
>
> This reader of this code doesn't understand why all this cookie stuff
> is in here. Please include code comments which explain the reason for
> the existence of this code.
>
ok
> > +static long kptr_obfuscate(long v, int type)
> > +{
> > + return (v ^ cookies[type][0]) * cookies[type][1];
> > +}
> > +
> > +/*
> > + * 0 - equal
> > + * 1 - less than
> > + * 2 - greater than
> > + * 3 - not equal but ordering unavailable
>
> what the heck does case 3 mean? Why is it here?
>
I'll add a comment. It's reserved for case where we might
need to disable gt/lt comparision result. Probably in future.
> > +
> > +#define KCMP_PTR(ptr1, ptr2, type) \
> > + kcmp_ptr((long)ptr1, (long)ptr2, type)
>
> ugh. This:
>
> static long kptr_obfuscate(void *p, enum you_forgot_to_name_the_enum type)
> {
> return ((long)p ^ cookies[type][0]) * cookies[type][1];
> }
>
> static int kcmp_task_pointers(void *task1, void *task2, size_t field_offset,
> enum you_forgot_to_name_the_enum type)
> {
> void **field1 = t1 + field_offset; /* points to a pointer in the task_struct */
> void **field2 = t1 + field_offset;
> long diff;
>
> diff = kptr_obfuscate(*field1, type) - kptr_obfuscate(*field2, type);
> return (diff < 0) | ((diff > 0) << 1);
> }
>
> ...
> ret = kcmp_task_pointers(task1, task2, offsetof(task_struct, mm),
> KCMP_VM);
> ...
>
> see? No nasty macros, it's type-correct and it uses only a single
> explicit typecast.
>
ok, i'll change it of course, but I personally like macros version more.
> > +/* A caller must be sure the task is presented in memory */
> "The caller must have pinned the task"
>
> > + if (!ptrace_may_access(task1, PTRACE_MODE_READ) ||
> > + !ptrace_may_access(task2, PTRACE_MODE_READ)) {
>
> Add a comment explaining this decision.
>
OK.
>
> ENOENT seems inappropriate here.
>
Which one should be better?
> > +static __init int kcmp_cookie_init(void)
> > +{
> > + int i, j;
> > +
> > + for (i = 0; i < KCMP_TYPES; i++) {
> > + for (j = 0; j < 2; j++) {
> > + get_random_bytes(&cookies[i][j],
> > + sizeof(cookies[i][j]));
> > + }
> > + cookies[i][1] |= (~(~0UL >> 1) | 1);
>
> hm, what's the point in writing a random number to cookies[i][1] and
> then immediately overwriting that with a constant?
It's '|=' , not '='.
Cyrill
next prev parent reply other threads:[~2012-01-24 21:46 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-23 14:20 [patch 0/4] A few patches in a sake of c/r functionality Cyrill Gorcunov
2012-01-23 14:20 ` [patch 1/4] fs, proc: Introduce /proc/<pid>/task/<tid>/children entry v8 Cyrill Gorcunov
2012-01-23 18:54 ` Kees Cook
2012-01-23 19:33 ` Cyrill Gorcunov
2012-01-23 20:29 ` Kees Cook
2012-01-23 20:39 ` Cyrill Gorcunov
2012-01-24 2:07 ` KAMEZAWA Hiroyuki
2012-01-24 6:53 ` Cyrill Gorcunov
2012-01-24 7:07 ` KAMEZAWA Hiroyuki
2012-01-24 7:21 ` Cyrill Gorcunov
2012-01-24 8:52 ` Eric W. Biederman
2012-01-24 9:11 ` Cyrill Gorcunov
2012-01-25 1:14 ` KOSAKI Motohiro
2012-01-25 2:11 ` Eric W. Biederman
2012-01-25 6:55 ` Cyrill Gorcunov
2012-01-25 15:29 ` Cyrill Gorcunov
2012-01-24 8:51 ` Cyrill Gorcunov
2012-01-24 23:53 ` Andrew Morton
2012-01-25 6:52 ` Cyrill Gorcunov
2012-01-23 14:20 ` [patch 2/4] [RFC] syscalls, x86: Add __NR_kcmp syscall v4 Cyrill Gorcunov
2012-01-23 18:48 ` H. Peter Anvin
2012-01-23 20:03 ` Cyrill Gorcunov
2012-01-24 2:16 ` KAMEZAWA Hiroyuki
2012-01-24 6:47 ` Cyrill Gorcunov
2012-01-24 7:04 ` H. Peter Anvin
2012-01-24 7:17 ` Cyrill Gorcunov
2012-01-24 7:20 ` KAMEZAWA Hiroyuki
2012-01-24 7:38 ` Cyrill Gorcunov
2012-01-24 7:40 ` KAMEZAWA Hiroyuki
2012-01-24 8:48 ` Cyrill Gorcunov
2012-01-24 20:20 ` KOSAKI Motohiro
2012-01-24 20:26 ` Cyrill Gorcunov
2012-01-24 20:44 ` Eric W. Biederman
2012-01-24 20:50 ` Cyrill Gorcunov
2012-01-24 21:20 ` Eric W. Biederman
2012-01-24 21:34 ` Cyrill Gorcunov
2012-01-24 21:22 ` Andrew Morton
2012-01-24 21:45 ` Andrew Morton
2012-01-24 21:46 ` H. Peter Anvin
2012-01-24 22:00 ` Andrew Morton
2012-01-24 22:52 ` H. Peter Anvin
2012-01-24 23:42 ` Andrew Morton
2012-01-24 21:46 ` Cyrill Gorcunov [this message]
2012-01-24 21:59 ` Andrew Morton
2012-01-24 22:54 ` Eric W. Biederman
2012-01-24 22:54 ` Andrew Morton
2012-01-24 21:25 ` Andrew Morton
2012-01-24 21:31 ` Cyrill Gorcunov
2012-01-24 8:49 ` Eric W. Biederman
2012-01-24 8:49 ` Cyrill Gorcunov
2012-01-23 14:20 ` [patch 3/4] c/r: procfs: add arg_start/end, env_start/end and exit_code members to /proc/$pid/stat Cyrill Gorcunov
2012-01-23 20:42 ` Kees Cook
2012-01-23 20:53 ` Cyrill Gorcunov
2012-01-24 23:59 ` Andrew Morton
2012-01-25 6:54 ` Cyrill Gorcunov
2012-01-25 7:12 ` Andrew Morton
2012-01-25 7:18 ` Cyrill Gorcunov
2012-01-23 14:20 ` [patch 4/4] c/r: prctl: Extend PR_SET_MM to set up more mm_struct entries Cyrill Gorcunov
2012-01-23 15:55 ` Cyrill Gorcunov
2012-01-23 20:02 ` Cyrill Gorcunov
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