From: Jiri Kosina jikos@kernel.org
From: Jiri Kosina jkosina@suse.cz
If 'prctl' mode of app2app protection from spectre_v2 is selected on kernel command-line, we are currently applying STIBP protection to tasks that restrict their indirect branch speculation via
prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, PR_SPEC_ENABLE, 0, 0);
Let's extend this to cover also SECCOMP tasks (analogically to how we apply SSBD protection).
According to software guidance:
"Setting ... STIBP ... on a logical processor prevents the predicted targets of indirect branches on any logical processor of that core from being controlled by software that executes (or executed previously) on another logical processor of the same core."
https://software.intel.com/security-software-guidance/insights/deep-dive-sin...
Hence setting STIBP on a sandboxed task will prevent the task from attacking other sibling threads or getting attacked.
Signed-off-by: Jiri Kosina jkosina@suse.cz Signed-off-by: Tim Chen tim.c.chen@linux.intel.com --- Documentation/admin-guide/kernel-parameters.txt | 7 ++++++- arch/x86/include/asm/nospec-branch.h | 1 + arch/x86/kernel/cpu/bugs.c | 21 +++++++++++++++++++-- 3 files changed, 26 insertions(+), 3 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index d2255f7..89b193c 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4227,12 +4227,17 @@ and STIBP mitigations against Spectre V2 attacks. If the CPU is not vulnerable, "off" is selected. If the CPU is vulnerable, the default mitigation - is "prctl". + is architecture and Kconfig dependent. See below. prctl - Enable mitigations per thread by restricting indirect branch speculation via prctl. Mitigation for a thread is not enabled by default to avoid mitigation overhead. The state of of the control is inherited on fork. + seccomp - Same as "prctl" above, but all seccomp threads + will disable SSB unless they explicitly opt out. + + Default mitigations: + If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
Not specifying this option is equivalent to spectre_v2_app2app=auto. diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index 69d2657..077ec54 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -231,6 +231,7 @@ enum spectre_v2_app2app_mitigation { SPECTRE_V2_APP2APP_NONE, SPECTRE_V2_APP2APP_STRICT, SPECTRE_V2_APP2APP_PRCTL, + SPECTRE_V2_APP2APP_SECCOMP, };
/* The Speculative Store Bypass disable variants */ diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 44f7127..f349b3f 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -138,6 +138,7 @@ enum spectre_v2_app2app_mitigation_cmd { SPECTRE_V2_APP2APP_CMD_FORCE, SPECTRE_V2_APP2APP_CMD_AUTO, SPECTRE_V2_APP2APP_CMD_PRCTL, + SPECTRE_V2_APP2APP_CMD_SECCOMP, };
static const char *spectre_v2_strings[] = { @@ -153,6 +154,7 @@ static const char *spectre_v2_app2app_strings[] = { [SPECTRE_V2_APP2APP_NONE] = "App-App Vulnerable", [SPECTRE_V2_APP2APP_STRICT] = "App-App Mitigation: Full app to app attack protection", [SPECTRE_V2_APP2APP_PRCTL] = "App-App Mitigation: Protect branch speculation restricted tasks", + [SPECTRE_V2_APP2APP_SECCOMP] = "App-App Mitigation: Protect branch speculation restricted and seccomp tasks", };
/* Lightweight mitigation: mitigate only tasks with TIF_SPEC_INDIR_BRANCH */ @@ -573,10 +575,17 @@ static void __init spectre_v2_select_mitigation(void) break;
case SPECTRE_V2_APP2APP_CMD_PRCTL: - case SPECTRE_V2_APP2APP_CMD_AUTO: app2app_mode = SPECTRE_V2_APP2APP_PRCTL; break;
+ case SPECTRE_V2_APP2APP_CMD_AUTO: + case SPECTRE_V2_APP2APP_CMD_SECCOMP: + if (IS_ENABLED(CONFIG_SECCOMP)) + app2app_mode = SPECTRE_V2_APP2APP_SECCOMP; + else + app2app_mode = SPECTRE_V2_APP2APP_PRCTL; + break; + case SPECTRE_V2_APP2APP_CMD_FORCE: app2app_mode = SPECTRE_V2_APP2APP_STRICT; break; @@ -595,7 +604,8 @@ static void __init spectre_v2_select_mitigation(void) set_app2app_mode: spectre_v2_app2app_enabled = app2app_mode; pr_info("%s\n", spectre_v2_app2app_strings[app2app_mode]); - if (app2app_mode == SPECTRE_V2_APP2APP_PRCTL) + if (app2app_mode == SPECTRE_V2_APP2APP_PRCTL || + app2app_mode == SPECTRE_V2_APP2APP_SECCOMP) static_branch_enable(&spectre_v2_app_lite);
/* Enable STIBP if appropriate */ @@ -849,6 +859,8 @@ void arch_seccomp_spec_mitigate(struct task_struct *task) { if (ssb_mode == SPEC_STORE_BYPASS_SECCOMP) ssb_prctl_set(task, PR_SPEC_FORCE_DISABLE); + if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_SECCOMP) + set_task_restrict_indir_branch(task, true); } #endif
@@ -879,6 +891,7 @@ static int indir_branch_prctl_get(struct task_struct *task) switch (spectre_v2_app2app_enabled) { case SPECTRE_V2_APP2APP_NONE: return PR_SPEC_ENABLE; + case SPECTRE_V2_APP2APP_SECCOMP: case SPECTRE_V2_APP2APP_PRCTL: if (task_spec_indir_branch_force_disable(task)) return PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE; @@ -1075,6 +1088,8 @@ static char *stibp_state(void) return ""; else if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_PRCTL) return ", STIBP-prctl"; + else if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_SECCOMP) + return ", STIBP-seccomp"; else return ", STIBP-all"; } @@ -1085,6 +1100,8 @@ static char *ibpb_state(void) return ""; else if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_PRCTL) return ", IBPB-prctl"; + else if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_SECCOMP) + return ", IBPB-seccomp"; else return ", IBPB-all"; }