From: Brian Gerst <brgerst@gmail.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.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>, Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH 09/20] signal/vm86_32: Replace open coded BUG_ON with an actual BUG_ON
Date: Fri, 12 Nov 2021 12:51:32 -0500 [thread overview]
Message-ID: <CAMzpN2jkK5sAv-Kg_kVnCEyVySiqeTdUORcC=AdG1gV6r8nUew@mail.gmail.com> (raw)
In-Reply-To: <874k8htmb2.fsf@email.froward.int.ebiederm.org>
On Fri, Nov 12, 2021 at 10:41 AM Eric W. Biederman
<ebiederm@xmission.com> wrote:
>
> "Eric W. Biederman" <ebiederm@xmission.com> writes:
>
> > The function save_v86_state is only called when userspace was
> > operating in vm86 mode before entering the kernel. Not having vm86
> > state in the task_struct should never happen. So transform the hand
> > rolled BUG_ON into an actual BUG_ON to make it clear what is
> > happening.
>
> Now that this change has been merged into Linus' tree I have a report
> that it is possible to trigger this new BUG_ON. Which obviously is not
> good.
>
> We could revert the change but I think that would just be shooting the
> messenger.
>
> Does anyone have an idea where to start to track down what is going on?
>
> A very quick skim through the code suggests that the only code path
> that calls save_v86_state that has not already accessed is
> current->thread.vm86 is handle_signal.
>
> Another quick look suggests that the only place where X86_VM_MASK gets
> set in eflags is in do_sys_vm86. So it appears do_sys_vm86 must
> be called before v8086_mode returns true in handle_signal.
>
> Which seems to suggest that the bug on can't trigger.
>
> But that is obviously wrong.
>
> I will keep digging but if anyone has some ideas that would be appreciated.
>
> Eric
It's possible that a null pointer was passed to the vm86 syscall.
Since vm86 mode usually requires memory to be mapped at address 0 this
wouldn't trigger a fault when reading the vm86_struct data. It should
be fine to remove !vm86->user_vm86 from the BUG_ON(), since the write
to userspace can handle a fault.
--
Brian Gerst
next prev parent reply other threads:[~2021-11-12 17:51 UTC|newest]
Thread overview: 95+ 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 17:43 ` [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
2021-10-21 16:02 ` Kees Cook
2021-10-21 16:25 ` 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
2021-10-21 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 [this message]
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 ` [PATCH v2 10/32] " Linus Torvalds
2021-10-25 21:28 ` 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
2021-10-21 8:09 ` Geert Uytterhoeven
2021-10-21 13:33 ` Eric W. Biederman
2021-10-21 8:32 ` Philippe Mathieu-Daudé
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