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x86/speculation: Enable prctl mode for spectre_v2_user 

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>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20181125185005.958421388@linutronix.de
This commit is contained in:
Thomas Gleixner 2018-11-25 19:33:54 +01:00
parent 9137bb27e6
commit 7cc765a67d
2 changed files with 38 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
Documentation/admin-guide/kernel-parameters.txt
View File

@ -4236,9 +4236,14 @@
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.

41
arch/x86/kernel/cpu/bugs.c
View File

@ -255,11 +255,13 @@ 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 {
@ -270,6 +272,7 @@ 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)
@ -324,12 +327,15 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
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 */
@ -340,6 +346,9 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
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;
}
@ -352,6 +361,12 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
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 */
@ -552,6 +567,15 @@ 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. */
@ -567,6 +591,7 @@ void arch_smt_update(void)
update_stibp_strict();
break;
case SPECTRE_V2_USER_PRCTL:
update_indir_branch_cond();
break;
}
@ -1038,7 +1063,8 @@ 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 "";
}
@ -1046,14 +1072,11 @@ 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 "";
}