2021-10-29 19:44:06

by Pawan Gupta

Subject: [PATCH ebpf v3] bpf: Disallow unprivileged bpf by default

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].

Sync with what many distros are currently applying, disable unprivileged
BPF by default. An admin can enable this at runtime, if necessary.

[1] https://ebpf.io/summit-2021-slides/eBPF_Summit_2021-Keynote-Daniel_Borkmann-BPF_and_Spectre.pdf

Signed-off-by: Pawan Gupta <[email protected]>
---
v3:
- Drop the conditional default for CONFIG_BPF_UNPRIV_DEFAULT_OFF until
we have an arch generic way to determine arch-common spectre type bugs.
[Mark Rutland, Daniel Borkmann].
- Also drop the patch to Generalize ARM's CONFIG_CPU_SPECTRE.
- Minor changes to commit message.

v2: https://lore.kernel.org/lkml/[email protected]/
- Generalize ARM's CONFIG_CPU_SPECTRE to be available for all architectures.
- Make CONFIG_BPF_UNPRIV_DEFAULT_OFF depend on CONFIG_CPU_SPECTRE.
- Updated commit message to reflect the dependency on CONFIG_CPU_SPECTRE.
- Add reference to BPF spectre presentation in commit message.

v1: https://lore.kernel.org/all/d37b01e70e65dced2659561ed5bc4b2ed1a50711.1635367330.git.pawan.kumar.gupta@linux.intel.com/

kernel/bpf/Kconfig | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/kernel/bpf/Kconfig b/kernel/bpf/Kconfig
index a82d6de86522..73d446294455 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
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

2021-11-01 11:58:55

by Mark Rutland

Subject: Re: [PATCH ebpf v3] bpf: Disallow unprivileged bpf by default

On Fri, Oct 29, 2021 at 12:43:54PM -0700, Pawan Gupta wrote:
> 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].
>
> Sync with what many distros are currently applying, disable unprivileged
> BPF by default. An admin can enable this at runtime, if necessary.
>
> [1] https://ebpf.io/summit-2021-slides/eBPF_Summit_2021-Keynote-Daniel_Borkmann-BPF_and_Spectre.pdf
>
> Signed-off-by: Pawan Gupta <[email protected]>

FWIW:

Acked-by: Mark Rutland <[email protected]>

Mark.

> ---
> v3:
> - Drop the conditional default for CONFIG_BPF_UNPRIV_DEFAULT_OFF until
> we have an arch generic way to determine arch-common spectre type bugs.
> [Mark Rutland, Daniel Borkmann].
> - Also drop the patch to Generalize ARM's CONFIG_CPU_SPECTRE.
> - Minor changes to commit message.
>
> v2: https://lore.kernel.org/lkml/[email protected]/
> - Generalize ARM's CONFIG_CPU_SPECTRE to be available for all architectures.
> - Make CONFIG_BPF_UNPRIV_DEFAULT_OFF depend on CONFIG_CPU_SPECTRE.
> - Updated commit message to reflect the dependency on CONFIG_CPU_SPECTRE.
> - Add reference to BPF spectre presentation in commit message.
>
> v1: https://lore.kernel.org/all/d37b01e70e65dced2659561ed5bc4b2ed1a50711.1635367330.git.pawan.kumar.gupta@linux.intel.com/
>
> kernel/bpf/Kconfig | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/kernel/bpf/Kconfig b/kernel/bpf/Kconfig
> index a82d6de86522..73d446294455 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
> 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
>