[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <ZTEmBU73nLnYMfEC@apocalypse>
Date: Thu, 19 Oct 2023 14:50:13 +0200
From: Andrea della Porta <aporta@...e.de>
To: Mark Rutland <mark.rutland@....com>
Cc: Andrea della Porta <andrea.porta@...e.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
nik.borisov@...e.com
Subject: Re: [PATCH 4/4] arm64: Make Aarch32 emulation boot time configurable
On 14:02 Wed 18 Oct , Mark Rutland wrote:
> On Wed, Oct 18, 2023 at 01:13:22PM +0200, Andrea della Porta wrote:
> > Distributions would like to reduce their attack surface as much as
> > possible but at the same time they'd want to retain flexibility to
> > cater to a variety of legacy software. This stems from the conjecture
> > that compat layer is likely rarely tested and could have latent
> > security bugs. Ideally distributions will set their default policy
> > and also give users the ability to override it as appropriate.
> >
> > To enable this use case, introduce CONFIG_AARCH32_EMULATION_DEFAULT_DISABLED
> > compile time option, which controls whether 32bit processes/syscalls
> > should be allowed or not. This option is aimed mainly at distributions
> > to set their preferred default behavior in their kernels.
> >
> > To allow users to override the distro's policy, introduce the
> > 'aarch32_emulation' parameter which allows overriding
> > CONFIG_AARCH32_EMULATION_DEFAULT_DISABLED state at boot time.
> >
> > Signed-off-by: Andrea della Porta <andrea.porta@...e.com>
> > ---
> > Documentation/admin-guide/kernel-parameters.txt | 7 +++++++
> > arch/arm64/Kconfig | 9 +++++++++
> > arch/arm64/kernel/entry-common.c | 8 +++++++-
> > 3 files changed, 23 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 0a1731a0f0ef..a41c5e6f5d2e 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -1,3 +1,10 @@
> > + aarch32_emulation= [ARM64]
> > + Format: <bool>
> > + When true, allows loading 32-bit programs and executing
> > + 32-bit syscalls, essentially overriding
> > + AARCH32_EMULATION_DEFAULT_DISABLED at boot time. when false,
> > + unconditionally disables AARCH32 emulation.
>
> Can we please drop the 'emulation' part of the name? We don't use that
> terminology on arm64 for regular execution of compat tasks, and only use that
> to refer to true emulation of deprecated instructions.
>
> We already have the 'allow_mismatched_32bit_el0' option; can we please us a
> name that aligns with that? e.g. 'allow_32bit_el0=false' to disable support.
>
Sure, 'allow_mismatched_32bit_el0' will do. I'll prepare a patch accordingly.
Andrea
Powered by blists - more mailing lists