Re: [PATCH ebpf v2 2/2] bpf: Make unprivileged bpf depend on CONFIG_CPU_SPECTRE
From: Mark Rutland <mark.rutland@arm.com>
Date: 2021-10-28 13:58:21
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On Wed, Oct 27, 2021 at 06:35:44PM -0700, Pawan Gupta wrote:
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Disabling unprivileged BPF would help prevent unprivileged users from creating the conditions required for potential speculative execution side-channel attacks on affected hardware. A deep dive on such attacks and mitigation is available here [1]. If an architecture selects CONFIG_CPU_SPECTRE, disable unprivileged BPF by default. An admin can enable this at runtime, if necessary. Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com> [1] https://ebpf.io/summit-2021-slides/eBPF_Summit_2021-Keynote-Daniel_Borkmann-BPF_and_Spectre.pdf --- kernel/bpf/Kconfig | 5 +++++ 1 file changed, 5 insertions(+)diff --git a/kernel/bpf/Kconfig b/kernel/bpf/Kconfig index a82d6de86522..510a5a73f9a2 100644 --- a/kernel/bpf/Kconfig +++ b/kernel/bpf/Kconfig@@ -64,6 +64,7 @@ config BPF_JIT_DEFAULT_ON config BPF_UNPRIV_DEFAULT_OFF bool "Disable unprivileged BPF by default" + default y if CPU_SPECTRE
Why can't this just be "default y"? This series makes that the case on x86, and if SW is going to have to deal with that we may as well do that everywhere, and say that on all architectures we leave it to the sysadmin or kernel builder to optin to permitting unprivileged BPF. If we can change the default for x86 I see no reason we can't change this globally, and we avoid tying this to CPU_SPECTRE specifically. Thanks, Mark.
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depends on BPF_SYSCALL help Disables unprivileged BPF by default by setting the corresponding@@ -72,6 +73,10 @@ config BPF_UNPRIV_DEFAULT_OFF disable it by setting it to 1 (from which no other transition to 0 is possible anymore). + Unprivileged BPF can be used to exploit potential speculative + execution side-channel vulnerabilities on affected hardware. If you + are concerned about it, answer Y. + source "kernel/bpf/preload/Kconfig" config BPF_LSM-- 2.31.1