From: Kees Cook <keescook@chromium.org>
To: Gabriel Krisman Bertazi <krisman@collabora.com>
Cc: Christian Brauner <christian.brauner@ubuntu.com>,
luto@kernel.org, tglx@linutronix.de, x86@kernel.org,
linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
willy@infradead.org, linux-kselftest@vger.kernel.org,
shuah@kernel.org, kernel@collabora.com
Subject: Re: [PATCH v6 1/9] kernel: Support TIF_SYSCALL_INTERCEPT flag
Date: Tue, 22 Sep 2020 12:42:53 -0700 [thread overview]
Message-ID: <202009221241.4C36E4EB@keescook> (raw)
In-Reply-To: <87wo14n9ru.fsf@collabora.com>
On Tue, Sep 08, 2020 at 12:59:49AM -0400, Gabriel Krisman Bertazi wrote:
> Christian Brauner <christian.brauner@ubuntu.com> writes:
>
> > On Fri, Sep 04, 2020 at 04:31:39PM -0400, Gabriel Krisman Bertazi wrote:
> >> index afe01e232935..3511c98a7849 100644
> >> --- a/include/linux/sched.h
> >> +++ b/include/linux/sched.h
> >> @@ -959,7 +959,11 @@ struct task_struct {
> >> kuid_t loginuid;
> >> unsigned int sessionid;
> >> #endif
> >> - struct seccomp seccomp;
> >> +
> >> + struct {
> >> + unsigned int syscall_intercept;
> >> + struct seccomp seccomp;
> >> + };
> >
> > If there's no specific reason to do this I'd not wrap this in an
> > anonymous struct. It doesn't really buy anything and there doesn't seem
> > to be precedent in struct task_struct right now. Also, if this somehow
> > adds padding it seems you might end up increasing the size of struct
> > task_struct more than necessary by accident? (I might be wrong
> > though.)
>
> Hi Christian,
>
> Thanks for your review on this and on the other patches of this series.
>
> I wrapped these to prevent struct layout randomization from separating
> the flags field from seccomp, as they are going to be used together and
> I was trying to reduce overhead to seccomp entry due to two cache misses
> when reading this structure. Measuring it seccomp_benchmark didn't show
> any difference with the unwrapped version, so perhaps it was a bit of
> premature optimization?
That should not be a thing to think about here. Structure randomization
already has a mode to protect against cache line issues. I would leave
this as just a new member; no wrapping struct.
--
Kees Cook
next prev parent reply other threads:[~2020-09-22 19:43 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-04 20:31 [PATCH v6 0/9] Syscall User Dispatch Gabriel Krisman Bertazi
2020-09-04 20:31 ` [PATCH v6 1/9] kernel: Support TIF_SYSCALL_INTERCEPT flag Gabriel Krisman Bertazi
2020-09-07 10:16 ` Christian Brauner
2020-09-08 4:59 ` Gabriel Krisman Bertazi
2020-09-22 19:42 ` Kees Cook [this message]
2020-09-23 20:28 ` Gabriel Krisman Bertazi
2020-09-11 9:32 ` peterz
2020-09-11 20:08 ` Gabriel Krisman Bertazi
2020-09-24 11:24 ` Peter Zijlstra
2020-09-22 19:44 ` Kees Cook
2020-09-23 20:18 ` Gabriel Krisman Bertazi
2020-09-23 20:49 ` Kees Cook
2020-09-25 8:00 ` Thomas Gleixner
2020-09-25 16:15 ` Gabriel Krisman Bertazi
2020-09-25 20:30 ` Kees Cook
2020-09-04 20:31 ` [PATCH v6 2/9] kernel: entry: Support TIF_SYSCAL_INTERCEPT on common entry code Gabriel Krisman Bertazi
2020-09-07 10:16 ` Christian Brauner
2020-09-11 9:35 ` peterz
2020-09-11 20:11 ` Gabriel Krisman Bertazi
2020-09-04 20:31 ` [PATCH v6 3/9] x86: vdso: Expose sigreturn address on vdso to the kernel Gabriel Krisman Bertazi
2020-09-22 19:40 ` Kees Cook
2020-09-04 20:31 ` [PATCH v6 4/9] signal: Expose SYS_USER_DISPATCH si_code type Gabriel Krisman Bertazi
2020-09-07 10:15 ` Christian Brauner
2020-09-22 19:39 ` Kees Cook
2020-09-04 20:31 ` [PATCH v6 5/9] kernel: Implement selective syscall userspace redirection Gabriel Krisman Bertazi
2020-09-05 11:24 ` Matthew Wilcox
2020-09-11 9:44 ` peterz
2020-09-04 20:31 ` [PATCH v6 6/9] kernel: entry: Support Syscall User Dispatch for common syscall entry Gabriel Krisman Bertazi
2020-09-07 10:15 ` Christian Brauner
2020-09-07 14:15 ` Andy Lutomirski
2020-09-07 14:25 ` Christian Brauner
2020-09-07 20:20 ` Andy Lutomirski
2020-09-11 9:46 ` peterz
2020-09-04 20:31 ` [PATCH v6 7/9] x86: Enable Syscall User Dispatch Gabriel Krisman Bertazi
2020-09-22 19:37 ` Kees Cook
2020-09-23 20:23 ` Gabriel Krisman Bertazi
2020-09-04 20:31 ` [PATCH v6 8/9] selftests: Add kselftest for syscall user dispatch Gabriel Krisman Bertazi
2020-09-22 19:35 ` Kees Cook
2020-09-04 20:31 ` [PATCH v6 9/9] doc: Document Syscall User Dispatch Gabriel Krisman Bertazi
2020-09-22 19:35 ` Kees Cook
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