[PATCH bpf-next] bpf: Inherit system settings for CPU security mitigations

[Yafang Shao <laoar.shao@gmail.com>]

Currently, there exists a system-wide setting related to CPU security
mitigations, denoted as 'mitigations='. When set to 'mitigations=off', it
deactivates all optional CPU mitigations. Therefore, if we implement a
system-wide 'mitigations=off' setting, it should inherently bypass Spectre
v1 and Spectre v4 in the BPF subsystem.

Please note that there is also a 'nospectre_v1' setting on x86 and ppc
architectures, though it is not currently exported. For the time being,
let's disregard it.

This idea emerged during our discussion about potential Spectre v1 attacks
with Luis[1].

[1]. https://lore.kernel.org/bpf/b4fc15f7-b204-767e-ebb9-fdb4233961fb@iogearbox.net/

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Cc: Luis Gerhorst <gerhorst@cs.fau.de>
---
 include/linux/bpf.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index a82efd34b741..61bde4520f5c 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2164,12 +2164,12 @@ static inline bool bpf_allow_uninit_stack(void)
 
 static inline bool bpf_bypass_spec_v1(void)
 {
-	return perfmon_capable();
+	return perfmon_capable() || cpu_mitigations_off();
 }
 
 static inline bool bpf_bypass_spec_v4(void)
 {
-	return perfmon_capable();
+	return perfmon_capable() || cpu_mitigations_off();
 }
 
 int bpf_map_new_fd(struct bpf_map *map, int flags);
-- 
2.30.1 (Apple Git-130)