[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20200210180740.GA24354@willie-the-truck>
Date: Mon, 10 Feb 2020 18:07:41 +0000
From: Will Deacon <will@...nel.org>
To: Mark Rutland <mark.rutland@....com>
Cc: James Morse <james.morse@....com>,
Sami Tolvanen <samitolvanen@...gle.com>,
Catalin Marinas <catalin.marinas@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Dave Martin <Dave.Martin@....com>,
Kees Cook <keescook@...omium.org>,
Laura Abbott <labbott@...hat.com>, Marc Zyngier <maz@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Jann Horn <jannh@...gle.com>,
Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>,
clang-built-linux@...glegroups.com,
kernel-hardening@...ts.openwall.com,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 09/11] arm64: disable SCS for hypervisor code
On Mon, Feb 10, 2020 at 06:03:28PM +0000, Mark Rutland wrote:
> On Mon, Feb 10, 2020 at 05:52:15PM +0000, Will Deacon wrote:
> > On Mon, Feb 10, 2020 at 05:18:58PM +0000, James Morse wrote:
> > > On 28/01/2020 18:49, Sami Tolvanen wrote:
> > > > Filter out CC_FLAGS_SCS and -ffixed-x18 for code that runs at a
> > > > different exception level.
> > >
> > > Hmmm, there are two things being disabled here.
> > >
> > > Stashing the lr in memory pointed to by VA won't work transparently at EL2 ... but
> > > shouldn't KVM's C code still treat x18 as a fixed register?
> >
> > My review of v6 suggested dropping the -ffixed-x18 as well, since it's only
> > introduced by SCS (in patch 5) and so isn't required by anything else. Why
> > do you think it's needed?
>
> When EL1 code calls up to hyp, it expects x18 to be preserved across the
> call, so hyp needs to either preserve it explicitly across a transitions
> from/to EL1 or always preserve it.
I thought we explicitly saved/restored it across the call after
af12376814a5 ("arm64: kvm: stop treating register x18 as caller save"). Is
that not sufficient?
> The latter is easiest since any code used by VHE hyp code will need x18
> saved anyway (ans so any common hyp code needs to).
I would personally prefer to split the VHE and non-VHE code so they can be
compiled with separate options.
Will
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
