linux-kernel - Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit?

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Message-ID: <CA+55aFycMWxCVY1p8n_D8nGz7Ky35uAmZMWm=zE5LBsqModiBg@mail.gmail.com>
Date:	Fri, 18 Dec 2015 12:37:23 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Dave Hansen <dave.hansen@...ux.intel.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	"H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
	Brian Gerst <brgerst@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@....de>
Subject: Re: Rethinking sigcontext's xfeatures slightly for PKRU's benefit?

On Fri, Dec 18, 2015 at 12:07 PM, Dave Hansen
<dave.hansen@...ux.intel.com> wrote:
>
> But, I think it's a small one.  Basically, RSP would have to pointing at
> a place which was allowed by protection keys for all of the sigframe
> setup.

Note that the whole "stack is special" is not at all a new issue.

It's the main reason why sigaltstack() and SS_ONSTACK exists. This is
in no way new to PKRU, people have had to handle the issue of
stack-related SIGSEGV faults for a long time.

So any application that uses PKRU and may play games that affects the
stack, will always have to have a separate "safe stack" that it uses
for signal handling. But that is in no way PKRU-specific, it's been
the case for a lot of other memory management faults.

                  Linus
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