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From: Linus Torvalds <torvalds@linux-foundation.org>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Andy Lutomirski <luto@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Oleg Nesterov <oleg@redhat.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Kees Cook <keescook@chromium.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	H Peter Anvin <hpa@zytor.com>
Subject: Re: [PATCH v2 10/32] signal/vm86_32: Properly send SIGSEGV when the vm86 state cannot be saved.
Date: Mon, 25 Oct 2021 14:12:03 -0700	[thread overview]
Message-ID: <CAHk-=whS0PL0NZrz2d8a3V+8=4szSZ6jqkg5fkjeaEjMN_NX8Q@mail.gmail.com> (raw)
In-Reply-To: <875ytkygfj.fsf_-_@disp2133>

On Mon, Oct 25, 2021 at 1:54 PM Eric W. Biederman <ebiederm@xmission.com> wrote:
>
> Update save_v86_state to always complete all of it's work except
> possibly some of the copies to userspace even if save_v86_state takes
> a fault.  This ensures that the kernel is always in a sane state, even
> if userspace has done something silly.

Well, honestly, with this change, you might as well replace the
force_sigsegv() with just a plain "force_sig()", and make it something
the process can catch.

The only thing that "force_sigsgv()" does is to make SIGSEGV
uncatchable. In contrast, a plain "force_sig()" just means that it
can't be ignored - but it can be caught, and it is fatal only when not
caught.

And with the "always complete the non-vm86 state restore" part change,
there's really no reason for it to not be caught.

Of course, the other case (where we have no state information for the
"enter vm86 mode" case) is still fatal, and is a "this should never
happen". But the "cannot write to the vm86 save state" thing isn't
technically fatal.

It should even be possible to write a test for it: passing a read-only
pointer to the vm86() system call. The vm86 entry will work (because
it only reads the vm86 state from it), but then at vm86 exit, writing
the state back will fail.

Anybody?

                 Linus

  parent reply	other threads:[~2021-10-25 21:12 UTC|newest]

Thread overview: 110+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-20 17:32 [PATCH 00/20] exit cleanups Eric W. Biederman
2021-10-20 17:32 ` [OpenRISC] " Eric W. Biederman
2021-10-20 17:32 ` Eric W. Biederman
2021-10-20 17:43 ` [PATCH 01/20] exit/doublefault: Remove apparently bogus comment about rewind_stack_do_exit Eric W. Biederman
2021-10-21 16:02   ` Kees Cook
2021-10-20 17:43 ` [PATCH 02/20] exit: Remove calls of do_exit after noreturn versions of die Eric W. Biederman
2021-10-20 17:43   ` [OpenRISC] " Eric W. Biederman
2021-10-21 16:02   ` Kees Cook
2021-10-21 16:02     ` [OpenRISC] " Kees Cook
2021-10-21 16:25     ` Eric W. Biederman
2021-10-21 16:25       ` [OpenRISC] " Eric W. Biederman
2021-10-20 17:43 ` [PATCH 03/20] reboot: Remove the unreachable panic after do_exit in reboot(2) Eric W. Biederman
2021-10-21 16:05   ` Kees Cook
2021-10-20 17:43 ` [PATCH 04/20] signal/sparc32: Remove unreachable do_exit in do_sparc_fault Eric W. Biederman
2021-10-21 16:05   ` Kees Cook
2021-10-20 17:43 ` [PATCH 05/20] signal/mips: Update (_save|_restore)_fp_context to fail with -EFAULT Eric W. Biederman
2021-10-21 16:06   ` Kees Cook
2021-10-24  4:24   ` Maciej W. Rozycki
2021-10-25 20:55     ` Eric W. Biederman
2021-10-24 15:27   ` Thomas Bogendoerfer
2021-10-20 17:43 ` [PATCH 06/20] signal/sh: Use force_sig(SIGKILL) instead of do_group_exit(SIGKILL) Eric W. Biederman
2021-10-20 19:57   ` Linus Torvalds
2021-10-27 14:24     ` Rich Felker
2021-10-21 16:08   ` Kees Cook
2021-10-20 17:43 ` [PATCH 07/20] signal/powerpc: On swapcontext failure force SIGSEGV Eric W. Biederman
2021-10-20 17:43   ` Eric W. Biederman
2021-10-21 16:09   ` Kees Cook
2021-10-21 16:09     ` Kees Cook
2021-10-20 17:43 ` [PATCH 08/20] signal/sparc: In setup_tsb_params convert open coded BUG into BUG Eric W. Biederman
2021-10-21 16:12   ` Kees Cook
2021-10-20 17:43 ` [PATCH 09/20] signal/vm86_32: Replace open coded BUG_ON with an actual BUG_ON Eric W. Biederman
2021-10-21 16:15   ` Kees Cook
2021-11-12 15:40   ` Eric W. Biederman
2021-11-12 17:51     ` Brian Gerst
2021-11-12 19:57       ` Eric W. Biederman
2021-11-12 20:40         ` Linus Torvalds
2021-11-12 21:03           ` Eric W. Biederman
2021-11-12 21:23             ` Linus Torvalds
2021-11-12 21:24               ` Linus Torvalds
2021-11-12 21:37                 ` [GIT PULL ] signal/vm86_32: Remove pointless test in BUG_ON Eric W. Biederman
2021-11-13 19:15                   ` pr-tracker-bot
2021-11-12 21:43                 ` [PATCH 09/20] signal/vm86_32: Replace open coded BUG_ON with an actual BUG_ON Eric W. Biederman
2021-10-20 17:43 ` [PATCH 10/20] signal/vm86_32: Properly send SIGSEGV when the vm86 state cannot be saved Eric W. Biederman
2021-10-21 16:16   ` Kees Cook
2021-10-21 17:02     ` Eric W. Biederman
2021-10-21 20:33       ` Kees Cook
2021-10-21 23:08   ` Andy Lutomirski
2021-10-24 16:06     ` Eric W. Biederman
     [not found]   ` <875ytkygfj.fsf_-_@disp2133>
2021-10-25 21:12     ` Linus Torvalds [this message]
2021-10-25 21:28       ` [PATCH v2 10/32] " Eric W. Biederman
2021-10-25 22:25     ` Andy Lutomirski
2021-10-25 23:45       ` Linus Torvalds
2021-10-26  0:21         ` Andy Lutomirski
2021-10-20 17:43 ` [PATCH 11/20] signal/s390: Use force_sigsegv in default_trap_handler Eric W. Biederman
2021-10-21 16:17   ` Kees Cook
2021-10-26  9:38   ` Christian Borntraeger
2021-10-28 15:56     ` Eric W. Biederman
2021-10-29 19:32       ` Eric W. Biederman
2021-10-20 17:43 ` [PATCH 12/20] exit/kthread: Have kernel threads return instead of calling do_exit Eric W. Biederman
2021-10-21 11:12   ` Christoph Hellwig
2021-10-21 15:11     ` Eric W. Biederman
2021-10-21 16:21   ` Kees Cook
2021-10-20 17:43 ` [PATCH 13/20] signal: Implement force_fatal_sig Eric W. Biederman
2021-10-20 20:05   ` Linus Torvalds
2021-10-20 21:25     ` Eric W. Biederman
2021-10-25 22:41     ` Andy Lutomirski
2021-10-25 23:15       ` Linus Torvalds
2021-10-26  4:45         ` Eric W. Biederman
2021-10-26  4:57         ` Eric W. Biederman
2021-10-26 16:15           ` Linus Torvalds
2021-10-28 16:33             ` Eric W. Biederman
2021-10-21 16:24   ` Kees Cook
2021-10-21 16:33     ` Eric W. Biederman
2021-10-21 16:39       ` Kees Cook
2021-10-20 17:44 ` [PATCH 14/20] exit/syscall_user_dispatch: Send ordinary signals on failure Eric W. Biederman
2021-10-21 16:25   ` Kees Cook
2021-10-21 16:37     ` Eric W. Biederman
2021-10-21 16:40       ` Kees Cook
2021-10-21 17:05         ` Eric W. Biederman
2021-10-25 22:32     ` Andy Lutomirski
2021-10-21 16:35   ` Gabriel Krisman Bertazi
2021-10-20 17:44 ` [PATCH 15/20] signal/sparc32: Exit with a fatal signal when try_to_clear_window_buffer fails Eric W. Biederman
2021-10-21 16:34   ` Kees Cook
2021-10-21 16:56     ` Eric W. Biederman
2021-10-20 17:44 ` [PATCH 16/20] signal/sparc32: In setup_rt_frame and setup_fram use force_fatal_sig Eric W. Biederman
2021-10-21 16:34   ` Kees Cook
2021-10-20 17:44 ` [PATCH 17/20] signal/x86: In emulate_vsyscall force a signal instead of calling do_exit Eric W. Biederman
2021-10-21 16:36   ` Kees Cook
2021-10-20 17:44 ` [PATCH 18/20] exit/rtl8723bs: Replace the macro thread_exit with a simple return 0 Eric W. Biederman
2021-10-21  7:06   ` Greg KH
2021-10-21 15:06     ` Eric W. Biederman
2021-10-21 16:37   ` Kees Cook
2021-10-20 17:44 ` [PATCH 19/20] exit/rtl8712: " Eric W. Biederman
2021-10-21  7:07   ` Greg KH
2021-10-21 16:37   ` Kees Cook
2021-10-20 17:44 ` [PATCH 20/20] exit/r8188eu: " Eric W. Biederman
2021-10-21  7:07   ` Greg KH
2021-10-21 16:37   ` Kees Cook
2021-10-20 21:51 ` [PATCH 21/20] signal: Replace force_sigsegv(SIGSEGV) with force_fatal_sig(SIGSEGV) Eric W. Biederman
2021-10-20 21:51   ` [OpenRISC] " Eric W. Biederman
2021-10-20 21:51   ` Eric W. Biederman
2021-10-21  8:09   ` Geert Uytterhoeven
2021-10-21  8:09     ` [OpenRISC] " Geert Uytterhoeven
2021-10-21  8:09     ` Geert Uytterhoeven
2021-10-21 13:33     ` Eric W. Biederman
2021-10-21 13:33       ` [OpenRISC] " Eric W. Biederman
2021-10-21 13:33       ` Eric W. Biederman
2021-10-21  8:32   ` Philippe Mathieu-Daudé
2021-10-21  8:32     ` [OpenRISC] " Philippe =?unknown-8bit?q?Mathieu-Daud=C3=A9?=
2021-10-21  8:32     ` Philippe Mathieu-Daudé

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