linux-kernel - Re: [PATCH 1/5] x86/mm/kaiser: Alternative ESPFIX

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Message-ID: <20171127223940.eedtdizvjqclz4xc@hirez.programming.kicks-ass.net>
Date:   Mon, 27 Nov 2017 23:39:40 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     linux-kernel@...r.kernel.org
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rik van Riel <riel@...hat.com>, daniel.gruss@...k.tugraz.at,
        hughd@...gle.com, keescook@...gle.com, linux-mm@...ck.org,
        michael.schwarz@...k.tugraz.at, moritz.lipp@...k.tugraz.at,
        richard.fellner@...dent.tugraz.at
Subject: Re: [PATCH 1/5] x86/mm/kaiser: Alternative ESPFIX

On Mon, Nov 27, 2017 at 11:31:11PM +0100, Peter Zijlstra wrote:
> Change the asm to do the CR3 switcheroo so we can remove the magic
> mappings.
> 
> Since RDI is unused after SWAPGS we can use it as a scratch reg for
> SWITCH_TO_KERNEL. And once we've computed the new RSP (in RAX) we no
> longer need RDI and can again use it as scratch reg for
> SWITCH_TO_USER.

Forgot to note; this passes tools/testing/selftests/x86/sigreturn_64.

> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>