From: Andrei Vagin <avagin@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
linux-um@lists.infradead.org, criu@openvz.org, avagin@google.com,
Andrew Morton <akpm@linux-foundation.org>,
Andy Lutomirski <luto@kernel.org>,
Anton Ivanov <anton.ivanov@cambridgegreys.com>,
Christian Brauner <christian.brauner@ubuntu.com>,
Dmitry Safonov <0x7f454c46@gmail.com>,
Ingo Molnar <mingo@redhat.com>, Jeff Dike <jdike@addtoit.com>,
Mike Rapoport <rppt@linux.ibm.com>,
Michael Kerrisk <mtk.manpages@gmail.com>,
Oleg Nesterov <oleg@redhat.com>,
Richard Weinberger <richard@nod.at>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 2/4] arch/x86: implement the process_vm_exec syscall
Date: Fri, 2 Jul 2021 15:21:22 -0700 [thread overview]
Message-ID: <YN+RYi5honrgjFAw@gmail.com> (raw)
In-Reply-To: <YN7TgV9RDJTRaY8R@hirez.programming.kicks-ass.net>
On Fri, Jul 02, 2021 at 10:51:13AM +0200, Peter Zijlstra wrote:
>
> I'm terrified of all of this...
>
> On Tue, Apr 13, 2021 at 10:52:15PM -0700, Andrei Vagin wrote:
>
> > +long swap_vm_exec_context(struct sigcontext __user *uctx)
> > +{
> > + struct sigcontext ctx = {};
> > + sigset_t set = {};
> > +
> > +
> > + if (copy_from_user(&ctx, uctx, CONTEXT_COPY_SIZE))
> > + return -EFAULT;
> > + /* A floating point state is managed from user-space. */
> > + if (ctx.fpstate != 0)
> > + return -EINVAL;
Here, we check that ctx doesn't have an FPU state.
> > + if (!user_access_begin(uctx, sizeof(*uctx)))
> > + return -EFAULT;
> > + unsafe_put_sigcontext(uctx, NULL, current_pt_regs(), (&set), Efault);
> > + user_access_end();
>
> But here you save the sigcontext without FPU state.
>
> > +
> > + if (__restore_sigcontext(current_pt_regs(), &ctx, 0))
> > + goto badframe;
>
> And here you restore sigcontext, *with* FPU state. At which point your
> FPU state is irrecoverably lost.
process_vm_exec doesn't change a process FPU state. Unlike signals, here
we can control it from a user-space. A process can set an FPU state
before process_vm_exec and then retore its FPU state after the
call.
This version of patches has a bug that I fixed in my tree when I
implemented the user-space part for gVisor. I didn't take into account
that restore_sigcontext(ctx) clears a process fpu state if ctx->fpstate
is zero. I moved fpu__restore_sig out from __restore_sigcontext to fix
this issue:
https://github.com/avagin/linux-task-diag/commit/55b7194d00ff
>
> Also, I'm not at all convinced this can ever do the right thing when the
> tasks don't agree on what the FPU state is. I suppose in the best case
> the save will EFAULT.
>
> > +
> > + return 0;
> > +Efault:
> > + user_access_end();
> > +badframe:
> > + signal_fault(current_pt_regs(), uctx, "swap_vm_exec_context");
> > + return -EFAULT;
> > +}
next prev parent reply other threads:[~2021-07-02 22:24 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-14 5:52 [PATCH 0/4 POC] Allow executing code and syscalls in another address space Andrei Vagin
2021-04-14 5:52 ` [PATCH 1/4] signal: add a helper to restore a process state from sigcontex Andrei Vagin
2021-04-14 5:52 ` [PATCH 2/4] arch/x86: implement the process_vm_exec syscall Andrei Vagin
2021-04-14 17:09 ` Oleg Nesterov
2021-04-23 6:59 ` Andrei Vagin
2021-06-28 16:13 ` Jann Horn
2021-06-28 16:30 ` Andy Lutomirski
2021-06-28 17:14 ` Jann Horn
2021-06-28 18:18 ` Eric W. Biederman
2021-06-29 1:01 ` Andrei Vagin
2021-07-02 6:22 ` Andrei Vagin
2021-07-02 11:51 ` Jann Horn
2021-07-02 20:40 ` Andy Lutomirski
2021-07-02 8:51 ` Peter Zijlstra
2021-07-02 22:21 ` Andrei Vagin [this message]
2021-07-02 20:56 ` Jann Horn
2021-07-02 22:48 ` Andrei Vagin
2021-04-14 5:52 ` [PATCH 3/4] arch/x86: allow to execute syscalls via process_vm_exec Andrei Vagin
2021-04-14 5:52 ` [PATCH 4/4] selftests: add tests for process_vm_exec Andrei Vagin
2021-04-14 6:46 ` [PATCH 0/4 POC] Allow executing code and syscalls in another address space Jann Horn
2021-04-14 22:10 ` Andrei Vagin
2021-07-02 6:57 ` Andrei Vagin
2021-07-02 15:12 ` Jann Horn
2021-07-18 0:38 ` Andrei Vagin
2021-04-14 7:22 ` Anton Ivanov
2021-04-14 7:34 ` Johannes Berg
2021-04-14 9:24 ` Benjamin Berg
2021-04-14 10:27 ` Florian Weimer
2021-04-14 11:24 ` Jann Horn
2021-04-14 12:20 ` Florian Weimer
2021-04-14 13:58 ` Jann Horn
2021-04-16 19:29 ` Kirill Smelkov
2021-04-17 16:28 ` sbaugh
2021-07-02 22:44 ` Andy Lutomirski
2021-07-18 1:34 ` Andrei Vagin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YN+RYi5honrgjFAw@gmail.com \
--to=avagin@gmail.com \
--cc=0x7f454c46@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=anton.ivanov@cambridgegreys.com \
--cc=avagin@google.com \
--cc=christian.brauner@ubuntu.com \
--cc=criu@openvz.org \
--cc=jdike@addtoit.com \
--cc=linux-api@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-um@lists.infradead.org \
--cc=luto@kernel.org \
--cc=mingo@redhat.com \
--cc=mtk.manpages@gmail.com \
--cc=oleg@redhat.com \
--cc=peterz@infradead.org \
--cc=richard@nod.at \
--cc=rppt@linux.ibm.com \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).