[PATCH 5.15 14/43] ARM: include unprivileged BPF status in Spectre V2 reporting

Greg Kroah-Hartman
2022-03-09T16:14:35Z

From: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

commit 25875aa71dfefd1959f07e626c4d285b88b27ac2 upstream.

The mitigations for Spectre-BHB are only applied when an exception
is taken, but when unprivileged BPF is enabled, userspace can
load BPF programs that can be used to exploit the problem.

When unprivileged BPF is enabled, report the vulnerable status via
the spectre_v2 sysfs file.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/arm/kernel/spectre.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

--- a/arch/arm/kernel/spectre.c
+++ b/arch/arm/kernel/spectre.c
@@ -1,9 +1,19 @@
// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/bpf.h>
#include <linux/cpu.h>
#include <linux/device.h>

#include <asm/spectre.h>

+static bool _unprivileged_ebpf_enabled(void)
+{
+#ifdef CONFIG_BPF_SYSCALL
+ return !sysctl_unprivileged_bpf_disabled;
+#else
+ return false
+#endif
+}
+
ssize_t cpu_show_spectre_v1(struct device *dev, struct device_attribute *attr,
char *buf)
{
@@ -31,6 +41,9 @@ ssize_t cpu_show_spectre_v2(struct devic
if (spectre_v2_state != SPECTRE_MITIGATED)
return sprintf(buf, "%s\n", "Vulnerable");

+ if (_unprivileged_ebpf_enabled())
+ return sprintf(buf, "Vulnerable: Unprivileged eBPF enabled\n");
+
switch (spectre_v2_methods) {
case SPECTRE_V2_METHOD_BPIALL:
method = "Branch predictor hardening";