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Message-ID: <CALCETrXy=ftik5U7nD9D+u8z-jLBOG_xX20QTDoP-CkV3=U2Vg@mail.gmail.com>
Date: Wed, 11 Mar 2015 15:26:13 -0700
From: Andy Lutomirski <luto@...capital.net>
To: Mikael Pettersson <mikpelinux@...il.com>
Cc: Jann Horn <jann@...jh.net>, Linux API <linux-api@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Michael Kerrisk <mtk.manpages@...il.com>,
Russell King <linux@....linux.org.uk>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
Jeff Dike <jdike@...toit.com>,
Richard Weinberger <richard@....at>,
Kees Cook <keescook@...omium.org>,
Will Drewry <wad@...omium.org>
Subject: Re: [PATCH] Don't allow blocking of signals using sigreturn.
On Wed, Mar 11, 2015 at 2:43 PM, Mikael Pettersson <mikpelinux@...il.com> wrote:
> Jann Horn writes:
> > Or should I throw this patch away and write a patch
> > for the prctl() manpage instead that documents that
> > being able to call sigreturn() implies being able to
> > effectively call sigprocmask(), at least on some
> > architectures like X86?
>
> Well, that is the semantics of sigreturn(). It is essentially
> setcontext() [which includes the actions of sigprocmask()], but
> with restrictions on parameter placement (at least on x86).
>
> You could introduce some setting to restrict that aspect for
> seccomp processes, but you can't change this for normal processes
> without breaking things.
Which leads to the interesting question: does anyone ever call
sigreturn with a different signal mask than the kernel put there
during signal delivery or, even more strangely, with a totally made up
context? I suspect that the former does happen, even if the latter
may be rare or completely implausible.
I certainly have code that modifies GPRs in the context prior to sigreturn.
--Andy
--
Andy Lutomirski
AMA Capital Management, LLC
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