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From: Al Viro <viro@zeniv.linux.org.uk>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Michael Schmitz <schmitzmic@gmail.com>,
	linux-arch <linux-arch@vger.kernel.org>,
	Jens Axboe <axboe@kernel.dk>, Oleg Nesterov <oleg@redhat.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Richard Henderson <rth@twiddle.net>,
	Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
	Matt Turner <mattst88@gmail.com>,
	alpha <linux-alpha@vger.kernel.org>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	linux-m68k <linux-m68k@lists.linux-m68k.org>,
	Arnd Bergmann <arnd@kernel.org>,
	Ley Foon Tan <ley.foon.tan@intel.com>, Tejun Heo <tj@kernel.org>,
	Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH 2/2] alpha/ptrace: Add missing switch_stack frames
Date: Wed, 16 Jun 2021 20:28:54 +0000	[thread overview]
Message-ID: <YMpfBsIvqbK0L4Gh@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <YMpeP0CrRUVKIysE@zeniv-ca.linux.org.uk>

On Wed, Jun 16, 2021 at 08:25:35PM +0000, Al Viro wrote:
> On Wed, Jun 16, 2021 at 01:32:50PM -0500, Eric W. Biederman wrote:
> 
> > -.macro	fork_like name
> > +.macro	allregs name
> >  	.align	4
> >  	.globl	alpha_\name
> >  	.ent	alpha_\name
> > +	.cfi_startproc
> >  alpha_\name:
> >  	.prologue 0
> > -	bsr	$1, do_switch_stack
> > +	SAVE_SWITCH_STACK
> >  	jsr	$26, sys_\name
> > -	ldq	$26, 56($sp)
> > -	lda	$sp, SWITCH_STACK_SIZE($sp)
> > +	RESTORE_SWITCH_STACK
> 
> 	No.  You've just added one hell of an overhead to fork(2),
> for no reason whatsoever.  sys_fork() et.al. does *NOT* modify the
> callee-saved registers; it's plain C.  So this change is complete
> BS.
> 
> > +allregs exit
> > +allregs exit_group
> 
> 	Details, please - what exactly makes exit(2) different from
> e.g. open(2)?

Ah... PTRACE_EVENT_EXIT garbage, fortunately having no counterparts in case of
open(2)...  Still, WTF would you want to restore callee-saved registers for
in case of exit(2)?

  reply	other threads:[~2021-06-16 20:29 UTC|newest]

Thread overview: 126+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-10 20:57 Kernel stack read with PTRACE_EVENT_EXIT and io_uring threads Eric W. Biederman
2021-06-10 20:57 ` Eric W. Biederman
2021-06-10 22:04 ` Linus Torvalds
2021-06-11 21:39   ` Eric W. Biederman
2021-06-11 23:26     ` Linus Torvalds
2021-06-13 21:54       ` Eric W. Biederman
2021-06-13 22:18         ` Linus Torvalds
2021-06-14  2:05           ` Michael Schmitz
2021-06-14  5:03             ` Michael Schmitz
2021-06-14 16:26               ` Eric W. Biederman
2021-06-14 22:26                 ` Michael Schmitz
2021-06-15 19:30                   ` Eric W. Biederman
2021-06-15 19:36                     ` [PATCH] alpha: Add extra switch_stack frames in exit, exec, and kernel threads Eric W. Biederman
2021-06-15 22:02                       ` Linus Torvalds
2021-06-16 16:32                         ` Eric W. Biederman
2021-06-16 18:29                           ` [PATCH 0/2] alpha/ptrace: Improved switch_stack handling Eric W. Biederman
2021-06-16 18:31                             ` [PATCH 1/2] alpha/ptrace: Record and handle the absence of switch_stack Eric W. Biederman
2021-06-16 20:00                               ` Linus Torvalds
2021-06-16 20:37                                 ` Linus Torvalds
2021-06-16 20:57                                   ` Eric W. Biederman
2021-06-16 21:02                                     ` Al Viro
2021-06-16 21:08                                     ` Linus Torvalds
2021-06-16 20:42                                 ` Eric W. Biederman
2021-06-16 20:17                               ` Al Viro
2021-06-21  2:01                               ` Michael Schmitz
2021-06-21  2:17                                 ` Linus Torvalds
2021-06-21  3:18                                   ` Michael Schmitz
2021-06-21  3:37                                     ` Linus Torvalds
2021-06-21  4:08                                       ` Michael Schmitz
2021-06-21  3:44                                     ` Al Viro
2021-06-21  5:31                                       ` Michael Schmitz
2021-06-21  2:27                                 ` Al Viro
2021-06-21  3:36                                   ` Michael Schmitz
2021-06-16 18:32                             ` [PATCH 2/2] alpha/ptrace: Add missing switch_stack frames Eric W. Biederman
2021-06-16 20:25                               ` Al Viro
2021-06-16 20:28                                 ` Al Viro [this message]
2021-06-16 20:49                                   ` Eric W. Biederman
2021-06-16 20:54                                     ` Al Viro
2021-06-16 20:47                                 ` Eric W. Biederman
2021-06-16 20:55                                   ` Al Viro
2021-06-16 20:50                       ` [PATCH] alpha: Add extra switch_stack frames in exit, exec, and kernel threads Al Viro
2021-06-15 20:56                     ` Kernel stack read with PTRACE_EVENT_EXIT and io_uring threads Michael Schmitz
2021-06-16  0:23                       ` Finn Thain
2021-06-15 21:58                     ` Linus Torvalds
2021-06-16 15:06                       ` Eric W. Biederman
2021-06-21 13:54                       ` Al Viro
2021-06-21 14:16                         ` Al Viro
2021-06-21 16:50                           ` Eric W. Biederman
2021-06-21 23:05                             ` Al Viro
2021-06-22 16:39                               ` Eric W. Biederman
2021-06-21 15:38                         ` Linus Torvalds
2021-06-21 18:59                         ` Al Viro
2021-06-21 19:22                           ` Linus Torvalds
2021-06-21 19:45                             ` Al Viro
2021-06-21 23:14                               ` Linus Torvalds
2021-06-21 23:23                                 ` Al Viro
2021-06-21 23:36                                   ` Linus Torvalds
2021-06-22 21:02                                     ` Eric W. Biederman
2021-06-22 21:48                                       ` Michael Schmitz
2021-06-23  5:26                                         ` Michael Schmitz
2021-06-23 14:36                                           ` Eric W. Biederman
2021-06-22  0:01                                 ` Michael Schmitz
2021-06-22 20:04                                 ` Michael Schmitz
2021-06-22 20:18                                   ` Al Viro
2021-06-22 21:57                                     ` Michael Schmitz
2021-06-21 20:03                             ` Eric W. Biederman
2021-06-21 23:15                               ` Linus Torvalds
2021-06-22 20:52                                 ` Eric W. Biederman
2021-06-23  0:41                                   ` Linus Torvalds
2021-06-23 14:33                                     ` Eric W. Biederman
2021-06-24 18:57                                       ` [PATCH 0/9] Refactoring exit Eric W. Biederman
2021-06-24 18:59                                         ` [PATCH 1/9] signal/sh: Use force_sig(SIGKILL) instead of do_group_exit(SIGKILL) Eric W. Biederman
2021-06-24 18:59                                         ` [PATCH 2/9] signal/seccomp: Refactor seccomp signal and coredump generation Eric W. Biederman
2021-06-26  3:17                                           ` Kees Cook
2021-06-28 19:21                                             ` Eric W. Biederman
2021-06-28 14:34                                           ` [signal/seccomp] 3fdd8c68c2: kernel-selftests.seccomp.seccomp_bpf.fail kernel test robot
2021-06-28 14:34                                             ` kernel test robot
2021-06-24 19:00                                         ` [PATCH 3/9] signal/seccomp: Dump core when there is only one live thread Eric W. Biederman
2021-06-26  3:20                                           ` Kees Cook
2021-06-24 19:01                                         ` [PATCH 4/9] signal: Factor start_group_exit out of complete_signal Eric W. Biederman
2021-06-24 20:04                                           ` Linus Torvalds
2021-06-25  8:47                                           ` kernel test robot
2021-06-25  8:47                                             ` kernel test robot
2021-06-26  3:24                                           ` Kees Cook
2021-06-24 19:01                                         ` [PATCH 5/9] signal/group_exit: Use start_group_exit in place of do_group_exit Eric W. Biederman
2021-06-26  3:35                                           ` Kees Cook
2021-06-24 19:02                                         ` [PATCH 6/9] signal: Fold do_group_exit into get_signal fixing io_uring threads Eric W. Biederman
2021-06-26  3:42                                           ` Kees Cook
2021-06-28 19:25                                             ` Eric W. Biederman
2021-06-24 19:02                                         ` [PATCH 7/9] signal: Make individual tasks exiting a first class concept Eric W. Biederman
2021-06-24 20:11                                           ` Linus Torvalds
2021-06-24 21:37                                             ` Eric W. Biederman
2021-06-24 19:03                                         ` [PATCH 8/9] signal/task_exit: Use start_task_exit in place of do_exit Eric W. Biederman
2021-06-26  5:56                                           ` Kees Cook
2021-06-24 19:03                                         ` [PATCH 9/9] signal: Move PTRACE_EVENT_EXIT into get_signal Eric W. Biederman
2021-06-24 22:45                                         ` [PATCH 0/9] Refactoring exit Al Viro
2021-06-27 22:13                                           ` Al Viro
2021-06-27 22:59                                             ` Michael Schmitz
2021-06-28  7:31                                               ` Geert Uytterhoeven
2021-06-28 16:20                                                 ` Eric W. Biederman
2021-06-28 17:14                                                 ` Michael Schmitz
2021-06-28 19:17                                                   ` Geert Uytterhoeven
2021-06-28 20:13                                                     ` Michael Schmitz
2021-06-28 21:18                                                       ` Geert Uytterhoeven
2021-06-28 23:42                                                         ` Michael Schmitz
2021-06-29 20:28                                                           ` [CFT][PATCH] exit/bdflush: Remove the deprecated bdflush system call Eric W. Biederman
2021-06-29 20:28                                                             ` Eric W. Biederman
2021-06-29 21:45                                                             ` Michael Schmitz
2021-06-29 21:45                                                               ` Michael Schmitz
2021-06-30  8:24                                                             ` Geert Uytterhoeven
2021-06-30  8:37                                                             ` Arnd Bergmann
2021-06-30 12:30                                                             ` Cyril Hrubis
2021-06-28 19:02                                           ` [PATCH 0/9] Refactoring exit Eric W. Biederman
2021-06-21 19:24                           ` Kernel stack read with PTRACE_EVENT_EXIT and io_uring threads Al Viro
2021-06-21 23:24                             ` Michael Schmitz
2021-06-16  7:38                     ` Geert Uytterhoeven
2021-06-16 19:40                       ` Michael Schmitz
2021-06-12 23:38 ` [PATCH v1] m68k: save extra registers on sys_exit and sys_exit_group syscall entry Michael Schmitz
2021-06-13 19:59   ` Linus Torvalds
2021-06-13 20:07     ` Michael Schmitz
2021-06-13 20:26       ` Linus Torvalds
2021-06-13 20:33         ` Linus Torvalds
2021-06-13 20:47         ` Linus Torvalds
2021-06-14  7:13   ` Michael Schmitz
2021-06-14  7:40     ` Andreas Schwab
2021-06-14  8:19       ` Michael Schmitz

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