The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 58c9a5060cb7cd529d49c93954cdafe81c1d642a Mon Sep 17 00:00:00 2001 From: James Morse james.morse@arm.com Date: Thu, 3 Mar 2022 16:53:56 +0000 Subject: [PATCH] arm64: proton-pack: Include unprivileged eBPF status in Spectre v2 mitigation reporting
The mitigations for Spectre-BHB are only applied when an exception is taken from user-space. The mitigation status is reported via the spectre_v2 sysfs vulnerabilities file.
When unprivileged eBPF is enabled the mitigation in the exception vectors can be avoided by an eBPF program.
When unprivileged eBPF is enabled, print a warning and report vulnerable via the sysfs vulnerabilities file.
Acked-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: James Morse james.morse@arm.com
diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c index d3fbff00993d..6d45c63c6454 100644 --- a/arch/arm64/kernel/proton-pack.c +++ b/arch/arm64/kernel/proton-pack.c @@ -18,6 +18,7 @@ */
#include <linux/arm-smccc.h> +#include <linux/bpf.h> #include <linux/cpu.h> #include <linux/device.h> #include <linux/nospec.h> @@ -111,6 +112,15 @@ static const char *get_bhb_affected_string(enum mitigation_state bhb_state) } }
+static bool _unprivileged_ebpf_enabled(void) +{ +#ifdef CONFIG_BPF_SYSCALL + return !sysctl_unprivileged_bpf_disabled; +#else + return false; +#endif +} + ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, char *buf) { @@ -130,6 +140,9 @@ ssize_t cpu_show_spectre_v2(struct device *dev, struct device_attribute *attr, v2_str = "CSV2"; fallthrough; case SPECTRE_MITIGATED: + if (bhb_state == SPECTRE_MITIGATED && _unprivileged_ebpf_enabled()) + return sprintf(buf, "Vulnerable: Unprivileged eBPF enabled\n"); + return sprintf(buf, "Mitigation: %s%s\n", v2_str, bhb_str); case SPECTRE_VULNERABLE: fallthrough; @@ -1125,3 +1138,16 @@ void __init spectre_bhb_patch_clearbhb(struct alt_instr *alt, *updptr++ = cpu_to_le32(aarch64_insn_gen_nop()); *updptr++ = cpu_to_le32(aarch64_insn_gen_nop()); } + +#ifdef CONFIG_BPF_SYSCALL +#define EBPF_WARN "Unprivileged eBPF is enabled, data leaks possible via Spectre v2 BHB attacks!\n" +void unpriv_ebpf_notify(int new_state) +{ + if (spectre_v2_state == SPECTRE_VULNERABLE || + spectre_bhb_state != SPECTRE_MITIGATED) + return; + + if (!new_state) + pr_err("WARNING: %s", EBPF_WARN); +} +#endif