[PATCH] x86/bpf: use bpf_capable() instead of capable(CAP_SYS_ADMIN)

[Serge E. Hallyn]

On Wed, Aug 06, 2025 at 04:31:05PM +0200, Ondrej Mosnacek wrote:
> Don't check against the overloaded CAP_SYS_ADMINin do_jit(), but instead
> use bpf_capable(), which checks against the more granular CAP_BPF first.
> Going straight to CAP_SYS_ADMIN may cause unnecessary audit log spam
> under SELinux, as privileged domains using BPF would usually only be
> allowed CAP_BPF and not CAP_SYS_ADMIN.
> 
> Link: https://bugzilla.redhat.com/show_bug.cgi?id=2369326
> Fixes: d4e89d212d40 ("x86/bpf: Call branch history clearing sequence on exit")
> Signed-off-by: Ondrej Mosnacek <omosnace at redhat.com>

So this seems correct, *provided* that we consider it within the purview of
CAP_BPF to be able to avoid clearing the branch history buffer.

I suspect that's the case, but it might warrant discussion.

Reviewed-by: Serge Hallyn <serge at hallyn.com>

> ---
>  arch/x86/net/bpf_jit_comp.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 15672cb926fc1..2a825e5745ca1 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -2591,8 +2591,7 @@ emit_jmp:
>  			seen_exit = true;
>  			/* Update cleanup_addr */
>  			ctx->cleanup_addr = proglen;
> -			if (bpf_prog_was_classic(bpf_prog) &&
> -			    !capable(CAP_SYS_ADMIN)) {
> +			if (bpf_prog_was_classic(bpf_prog) && !bpf_capable()) {
>  				u8 *ip = image + addrs[i - 1];
>  
>  				if (emit_spectre_bhb_barrier(&prog, ip, bpf_prog))
> -- 
> 2.50.1
>