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From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc: "Mark Rutland" <mark.rutland@arm.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"Dave Hansen" <dave.hansen@linux.intel.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Masahiro Yamada" <masahiroy@kernel.org>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	"Sami Tolvanen" <samitolvanen@google.com>,
	"Colin Ian King" <colin.king@canonical.com>,
	"Frederic Weisbecker" <frederic@kernel.org>,
	"Mike Rapoport" <rppt@kernel.org>,
	"YiFei Zhu" <yifeifz2@illinois.edu>,
	"Steven Rostedt (VMware)" <rostedt@goodmis.org>,
	"Viresh Kumar" <viresh.kumar@linaro.org>,
	"Andrey Konovalov" <andreyknvl@gmail.com>,
	"Wang Kefeng" <wangkefeng.wang@huawei.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Nathan Chancellor" <nathan@kernel.org>,
	"Nick Desaulniers" <ndesaulniers@google.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	bpf@vger.kernel.org
Subject: Re: [PATCH v2 1/2] arch/Kconfig: Make CONFIG_CPU_SPECTRE available for all architectures
Date: Fri, 29 Oct 2021 11:08:35 +0100	[thread overview]
Message-ID: <YXvIIwkfYcXEBf97@shell.armlinux.org.uk> (raw)
In-Reply-To: <20211028193658.7n2oehp6yogyqbwq@gupta-dev2.localdomain>

On Thu, Oct 28, 2021 at 12:36:58PM -0700, Pawan Gupta wrote:
> Isn't ARM already using CPU_SPECTRE for selecting things:
> 
> 	config HARDEN_BRANCH_PREDICTOR
> 	     bool "Harden the branch predictor against aliasing attacks" if EXPERT
> 	     depends on CPU_SPECTRE
> 
> This was the whole motivation for doing the same for x86.
> 
> Adding a condition for all architectures is also okay, but its going to
> a little messier:
> 
> 	 config BPF_UNPRIV_DEFAULT_OFF
> 	        default y if X86 || ARM || ...

It doesn't have to be (but sadly we end up repeating "DEFAULT"):

config BPF_UNPRIV_DEFAULT_OFF_DEFAULT
	bool

config BPF_UNPRIV_DEFAULT_OFF
	bool "Disable unprivileged BPF by default"
	default BPF_UNPRIV_DEFAULT_OFF_DEFAULT

Then architectures can select BPF_UNPRIV_DEFAULT_OFF_DEFAULT if they
wish this to be defaulted to "yes".

However, please note that this has limited use given that the
BPF_UNPRIV_DEFAULT_OFF option has been around for a while now. Any
existing configuration that mentions this symbol will override any
default specified in the Kconfig files if the option is user-visible.

So, IMHO, defaults need to be set correctly from the point in time
that the option is introduced.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

WARNING: multiple messages have this Message-ID (diff)
From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc: "Mark Rutland" <mark.rutland@arm.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"Dave Hansen" <dave.hansen@linux.intel.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Masahiro Yamada" <masahiroy@kernel.org>,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>,
	"Sami Tolvanen" <samitolvanen@google.com>,
	"Colin Ian King" <colin.king@canonical.com>,
	"Frederic Weisbecker" <frederic@kernel.org>,
	"Mike Rapoport" <rppt@kernel.org>,
	"YiFei Zhu" <yifeifz2@illinois.edu>,
	"Steven Rostedt (VMware)" <rostedt@goodmis.org>,
	"Viresh Kumar" <viresh.kumar@linaro.org>,
	"Andrey Konovalov" <andreyknvl@gmail.com>,
	"Wang Kefeng" <wangkefeng.wang@huawei.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Nathan Chancellor" <nathan@kernel.org>,
	"Nick Desaulniers" <ndesaulniers@google.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	bpf@vger.kernel.org
Subject: Re: [PATCH v2 1/2] arch/Kconfig: Make CONFIG_CPU_SPECTRE available for all architectures
Date: Fri, 29 Oct 2021 11:08:35 +0100	[thread overview]
Message-ID: <YXvIIwkfYcXEBf97@shell.armlinux.org.uk> (raw)
In-Reply-To: <20211028193658.7n2oehp6yogyqbwq@gupta-dev2.localdomain>

On Thu, Oct 28, 2021 at 12:36:58PM -0700, Pawan Gupta wrote:
> Isn't ARM already using CPU_SPECTRE for selecting things:
> 
> 	config HARDEN_BRANCH_PREDICTOR
> 	     bool "Harden the branch predictor against aliasing attacks" if EXPERT
> 	     depends on CPU_SPECTRE
> 
> This was the whole motivation for doing the same for x86.
> 
> Adding a condition for all architectures is also okay, but its going to
> a little messier:
> 
> 	 config BPF_UNPRIV_DEFAULT_OFF
> 	        default y if X86 || ARM || ...

It doesn't have to be (but sadly we end up repeating "DEFAULT"):

config BPF_UNPRIV_DEFAULT_OFF_DEFAULT
	bool

config BPF_UNPRIV_DEFAULT_OFF
	bool "Disable unprivileged BPF by default"
	default BPF_UNPRIV_DEFAULT_OFF_DEFAULT

Then architectures can select BPF_UNPRIV_DEFAULT_OFF_DEFAULT if they
wish this to be defaulted to "yes".

However, please note that this has limited use given that the
BPF_UNPRIV_DEFAULT_OFF option has been around for a while now. Any
existing configuration that mentions this symbol will override any
default specified in the Kconfig files if the option is user-visible.

So, IMHO, defaults need to be set correctly from the point in time
that the option is introduced.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2021-10-29 10:09 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-28  1:32 [PATCH ebpf v2 0/2] Unprivileged BPF default Pawan Gupta
2021-10-28  1:33 ` [PATCH v2 1/2] arch/Kconfig: Make CONFIG_CPU_SPECTRE available for all architectures Pawan Gupta
2021-10-28  1:33   ` Pawan Gupta
2021-10-28  5:27   ` Greg KH
2021-10-28  5:27     ` Greg KH
2021-10-28 13:49   ` Mark Rutland
2021-10-28 13:49     ` Mark Rutland
2021-10-28 19:36     ` Pawan Gupta
2021-10-28 19:36       ` Pawan Gupta
2021-10-29  9:22       ` Mark Rutland
2021-10-29  9:22         ` Mark Rutland
2021-10-29 16:05         ` Daniel Borkmann
2021-10-29 16:05           ` Daniel Borkmann
2021-10-29 19:15           ` Pawan Gupta
2021-10-29 19:15             ` Pawan Gupta
2021-10-29 10:08       ` Russell King (Oracle) [this message]
2021-10-29 10:08         ` Russell King (Oracle)
2021-10-29 22:51         ` Pawan Gupta
2021-10-29 22:51           ` Pawan Gupta
2021-10-28  1:35 ` [PATCH ebpf v2 2/2] bpf: Make unprivileged bpf depend on CONFIG_CPU_SPECTRE Pawan Gupta
2021-10-28  5:34   ` Greg KH
2021-10-28 19:38     ` Pawan Gupta
2021-10-28 13:57   ` Mark Rutland
2021-10-28 16:44     ` Greg KH

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