x86/bpf: do not audit capability check in do_jit()

The failure of this check only results in a security mitigation being
applied, slightly affecting performance of the compiled BPF program. It
doesn't result in a failed syscall, an thus auditing a failed LSM
permission check for it is unwanted. For example with SELinux, it causes
a denial to be reported for confined processes running as root, which
tends to be flagged as a problem to be fixed in the policy. Yet
dontauditing or allowing CAP_SYS_ADMIN to the domain may not be
desirable, as it would allow/silence also other checks - either going
against the principle of least privilege or making debugging potentially
harder.

Fix it by changing it from capable() to ns_capable_noaudit(), which
instructs the LSMs to not audit the resulting denials.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=2369326
Fixes: d4e89d2 ("x86/bpf: Call branch history clearing sequence on exit")
Signed-off-by: Ondrej Mosnacek <[email protected]>
Reviewed-by: Paul Moore <[email protected]>

Author: WOnder93

arch/x86/net/bpf_jit_comp.c

@@ -2701,7 +2701,7 @@ st:			if (is_imm8(insn->off))
 			/* Update cleanup_addr */
 			ctx->cleanup_addr = proglen;
 			if (bpf_prog_was_classic(bpf_prog) &&
-			    !capable(CAP_SYS_ADMIN)) {
+			    !ns_capable_noaudit(&init_user_ns, CAP_SYS_ADMIN)) {
 				u8 *ip = image + addrs[i - 1];
 
 				if (emit_spectre_bhb_barrier(&prog, ip, bpf_prog))