From: Thomas Gleixner tglx@linutronix.de
commit 7cc765a67d8e04ef7d772425ca5a2a1e2b894c15 upstream.
Now that all prerequisites are in place:
- Add the prctl command line option
- Default the 'auto' mode to 'prctl'
- When SMT state changes, update the static key which controls the conditional STIBP evaluation on context switch.
- At init update the static key which controls the conditional IBPB evaluation on context switch.
Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Ingo Molnar mingo@kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: Andy Lutomirski luto@kernel.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Jiri Kosina jkosina@suse.cz Cc: Tom Lendacky thomas.lendacky@amd.com Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: David Woodhouse dwmw@amazon.co.uk Cc: Tim Chen tim.c.chen@linux.intel.com Cc: Andi Kleen ak@linux.intel.com Cc: Dave Hansen dave.hansen@intel.com Cc: Casey Schaufler casey.schaufler@intel.com Cc: Asit Mallick asit.k.mallick@intel.com Cc: Arjan van de Ven arjan@linux.intel.com Cc: Jon Masters jcm@redhat.com Cc: Waiman Long longman9394@gmail.com Cc: Greg KH gregkh@linuxfoundation.org Cc: Dave Stewart david.c.stewart@intel.com Cc: Kees Cook keescook@chromium.org Link: https://lkml.kernel.org/r/20181125185005.958421388@linutronix.de [bwh: Backported to 4.4: adjust filename] Signed-off-by: Ben Hutchings ben@decadent.org.uk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- Documentation/kernel-parameters.txt | 7 +++++- arch/x86/kernel/cpu/bugs.c | 41 ++++++++++++++++++++++++++++-------- 2 files changed, 38 insertions(+), 10 deletions(-)
--- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -3646,9 +3646,14 @@ bytes respectively. Such letter suffixes off - Unconditionally disable mitigations. Is enforced by spectre_v2=off
+ prctl - Indirect branch speculation is enabled, + but mitigation can be enabled via prctl + per thread. The mitigation control state + is inherited on fork. + auto - Kernel selects the mitigation depending on the available CPU features and vulnerability. - Default is off. + Default is prctl.
Not specifying this option is equivalent to spectre_v2_user=auto. --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -244,11 +244,13 @@ enum spectre_v2_user_cmd { SPECTRE_V2_USER_CMD_NONE, SPECTRE_V2_USER_CMD_AUTO, SPECTRE_V2_USER_CMD_FORCE, + SPECTRE_V2_USER_CMD_PRCTL, };
static const char * const spectre_v2_user_strings[] = { [SPECTRE_V2_USER_NONE] = "User space: Vulnerable", [SPECTRE_V2_USER_STRICT] = "User space: Mitigation: STIBP protection", + [SPECTRE_V2_USER_PRCTL] = "User space: Mitigation: STIBP via prctl", };
static const struct { @@ -259,6 +261,7 @@ static const struct { { "auto", SPECTRE_V2_USER_CMD_AUTO, false }, { "off", SPECTRE_V2_USER_CMD_NONE, false }, { "on", SPECTRE_V2_USER_CMD_FORCE, true }, + { "prctl", SPECTRE_V2_USER_CMD_PRCTL, false }, };
static void __init spec_v2_user_print_cond(const char *reason, bool secure) @@ -312,12 +315,15 @@ spectre_v2_user_select_mitigation(enum s smt_possible = false;
switch (spectre_v2_parse_user_cmdline(v2_cmd)) { - case SPECTRE_V2_USER_CMD_AUTO: case SPECTRE_V2_USER_CMD_NONE: goto set_mode; case SPECTRE_V2_USER_CMD_FORCE: mode = SPECTRE_V2_USER_STRICT; break; + case SPECTRE_V2_USER_CMD_AUTO: + case SPECTRE_V2_USER_CMD_PRCTL: + mode = SPECTRE_V2_USER_PRCTL; + break; }
/* Initialize Indirect Branch Prediction Barrier */ @@ -328,6 +334,9 @@ spectre_v2_user_select_mitigation(enum s case SPECTRE_V2_USER_STRICT: static_branch_enable(&switch_mm_always_ibpb); break; + case SPECTRE_V2_USER_PRCTL: + static_branch_enable(&switch_mm_cond_ibpb); + break; default: break; } @@ -340,6 +349,12 @@ spectre_v2_user_select_mitigation(enum s if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED) return;
+ /* + * If SMT is not possible or STIBP is not available clear the STIPB + * mode. + */ + if (!smt_possible || !boot_cpu_has(X86_FEATURE_STIBP)) + mode = SPECTRE_V2_USER_NONE; set_mode: spectre_v2_user = mode; /* Only print the STIBP mode when SMT possible */ @@ -547,6 +562,15 @@ static void update_stibp_strict(void) on_each_cpu(update_stibp_msr, NULL, 1); }
+/* Update the static key controlling the evaluation of TIF_SPEC_IB */ +static void update_indir_branch_cond(void) +{ + if (sched_smt_active()) + static_branch_enable(&switch_to_cond_stibp); + else + static_branch_disable(&switch_to_cond_stibp); +} + void arch_smt_update(void) { /* Enhanced IBRS implies STIBP. No update required. */ @@ -562,6 +586,7 @@ void arch_smt_update(void) update_stibp_strict(); break; case SPECTRE_V2_USER_PRCTL: + update_indir_branch_cond(); break; }
@@ -950,7 +975,8 @@ static char *stibp_state(void) case SPECTRE_V2_USER_STRICT: return ", STIBP: forced"; case SPECTRE_V2_USER_PRCTL: - return ""; + if (static_key_enabled(&switch_to_cond_stibp)) + return ", STIBP: conditional"; } return ""; } @@ -958,14 +984,11 @@ static char *stibp_state(void) static char *ibpb_state(void) { if (boot_cpu_has(X86_FEATURE_IBPB)) { - switch (spectre_v2_user) { - case SPECTRE_V2_USER_NONE: - return ", IBPB: disabled"; - case SPECTRE_V2_USER_STRICT: + if (static_key_enabled(&switch_mm_always_ibpb)) return ", IBPB: always-on"; - case SPECTRE_V2_USER_PRCTL: - return ""; - } + if (static_key_enabled(&switch_mm_cond_ibpb)) + return ", IBPB: conditional"; + return ", IBPB: disabled"; } return ""; }