arm64: bpf: Add BHB mitigation to the epilogue for cBPF programs

A malicious BPF program may manipulate the branch history to influence
what the hardware speculates will happen next.

On exit from a BPF program, emit the BHB mititgation sequence.

This is only applied for 'classic' cBPF programs that are loaded by
seccomp.

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 1 insertions, 1 deletions

diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
index 3154094a9e33..4459b613077e 100644
--- a/arch/arm64/kernel/proton-pack.c
+++ b/arch/arm64/kernel/proton-pack.c
@@ -1021,7 +1021,7 @@ static void this_cpu_set_vectors(enum arm64_bp_harden_el1_vectors slot)
 	isb();
 }
 
-static bool __read_mostly __nospectre_bhb;
+bool __read_mostly __nospectre_bhb;
 static int __init parse_spectre_bhb_param(char *str)
 {
 	__nospectre_bhb = true;