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Date: Wed, 28 Nov 2018 06:29:37 -0800
From: tip-bot for Thomas Gleixner <tipbot@...or.com>
To: linux-tip-commits@...r.kernel.org
Cc: aarcange@...hat.com, longman9394@...il.com,
david.c.stewart@...el.com, tim.c.chen@...ux.intel.com,
asit.k.mallick@...el.com, arjan@...ux.intel.com, hpa@...or.com,
gregkh@...uxfoundation.org, ak@...ux.intel.com,
casey.schaufler@...el.com, dwmw@...zon.co.uk, tglx@...utronix.de,
jpoimboe@...hat.com, keescook@...omium.org, mingo@...nel.org,
jcm@...hat.com, peterz@...radead.org,
torvalds@...ux-foundation.org, jkosina@...e.cz, luto@...nel.org,
linux-kernel@...r.kernel.org, thomas.lendacky@....com,
dave.hansen@...el.com
Subject: [tip:x86/pti] x86/speculation: Add command line control for
indirect branch speculation
Commit-ID: fa1202ef224391b6f5b26cdd44cc50495e8fab54
Gitweb: https://git.kernel.org/tip/fa1202ef224391b6f5b26cdd44cc50495e8fab54
Author: Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Sun, 25 Nov 2018 19:33:45 +0100
Committer: Thomas Gleixner <tglx@...utronix.de>
CommitDate: Wed, 28 Nov 2018 11:57:10 +0100
x86/speculation: Add command line control for indirect branch speculation
Add command line control for user space indirect branch speculation
mitigations. The new option is: spectre_v2_user=
The initial options are:
- on: Unconditionally enabled
- off: Unconditionally disabled
-auto: Kernel selects mitigation (default off for now)
When the spectre_v2= command line argument is either 'on' or 'off' this
implies that the application to application control follows that state even
if a contradicting spectre_v2_user= argument is supplied.
Originally-by: Tim Chen <tim.c.chen@...ux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Jiri Kosina <jkosina@...e.cz>
Cc: Tom Lendacky <thomas.lendacky@....com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: David Woodhouse <dwmw@...zon.co.uk>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Casey Schaufler <casey.schaufler@...el.com>
Cc: Asit Mallick <asit.k.mallick@...el.com>
Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Jon Masters <jcm@...hat.com>
Cc: Waiman Long <longman9394@...il.com>
Cc: Greg KH <gregkh@...uxfoundation.org>
Cc: Dave Stewart <david.c.stewart@...el.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: stable@...r.kernel.org
Link: https://lkml.kernel.org/r/20181125185005.082720373@linutronix.de
---
Documentation/admin-guide/kernel-parameters.txt | 32 +++++-
arch/x86/include/asm/nospec-branch.h | 10 ++
arch/x86/kernel/cpu/bugs.c | 133 +++++++++++++++++++++---
3 files changed, 156 insertions(+), 19 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 19f4423e70d9..b6e5b33b9d75 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4194,9 +4194,13 @@
spectre_v2= [X86] Control mitigation of Spectre variant 2
(indirect branch speculation) vulnerability.
+ The default operation protects the kernel from
+ user space attacks.
- on - unconditionally enable
- off - unconditionally disable
+ on - unconditionally enable, implies
+ spectre_v2_user=on
+ off - unconditionally disable, implies
+ spectre_v2_user=off
auto - kernel detects whether your CPU model is
vulnerable
@@ -4206,6 +4210,12 @@
CONFIG_RETPOLINE configuration option, and the
compiler with which the kernel was built.
+ Selecting 'on' will also enable the mitigation
+ against user space to user space task attacks.
+
+ Selecting 'off' will disable both the kernel and
+ the user space protections.
+
Specific mitigations can also be selected manually:
retpoline - replace indirect branches
@@ -4215,6 +4225,24 @@
Not specifying this option is equivalent to
spectre_v2=auto.
+ spectre_v2_user=
+ [X86] Control mitigation of Spectre variant 2
+ (indirect branch speculation) vulnerability between
+ user space tasks
+
+ on - Unconditionally enable mitigations. Is
+ enforced by spectre_v2=on
+
+ off - Unconditionally disable mitigations. Is
+ enforced by spectre_v2=off
+
+ auto - Kernel selects the mitigation depending on
+ the available CPU features and vulnerability.
+ Default is off.
+
+ Not specifying this option is equivalent to
+ spectre_v2_user=auto.
+
spec_store_bypass_disable=
[HW] Control Speculative Store Bypass (SSB) Disable mitigation
(Speculative Store Bypass vulnerability)
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index c202a64edd95..be0b0aa780e2 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -3,6 +3,8 @@
#ifndef _ASM_X86_NOSPEC_BRANCH_H_
#define _ASM_X86_NOSPEC_BRANCH_H_
+#include <linux/static_key.h>
+
#include <asm/alternative.h>
#include <asm/alternative-asm.h>
#include <asm/cpufeatures.h>
@@ -226,6 +228,12 @@ enum spectre_v2_mitigation {
SPECTRE_V2_IBRS_ENHANCED,
};
+/* The indirect branch speculation control variants */
+enum spectre_v2_user_mitigation {
+ SPECTRE_V2_USER_NONE,
+ SPECTRE_V2_USER_STRICT,
+};
+
/* The Speculative Store Bypass disable variants */
enum ssb_mitigation {
SPEC_STORE_BYPASS_NONE,
@@ -303,6 +311,8 @@ do { \
preempt_enable(); \
} while (0)
+DECLARE_STATIC_KEY_FALSE(switch_to_cond_stibp);
+
#endif /* __ASSEMBLY__ */
/*
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 4f5a6319dca6..3a223cce1fac 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -54,6 +54,9 @@ static u64 __ro_after_init x86_spec_ctrl_mask = SPEC_CTRL_IBRS;
u64 __ro_after_init x86_amd_ls_cfg_base;
u64 __ro_after_init x86_amd_ls_cfg_ssbd_mask;
+/* Control conditional STIPB in switch_to() */
+DEFINE_STATIC_KEY_FALSE(switch_to_cond_stibp);
+
void __init check_bugs(void)
{
identify_boot_cpu();
@@ -199,6 +202,9 @@ static void x86_amd_ssb_disable(void)
static enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init =
SPECTRE_V2_NONE;
+static enum spectre_v2_user_mitigation spectre_v2_user __ro_after_init =
+ SPECTRE_V2_USER_NONE;
+
#ifdef RETPOLINE
static bool spectre_v2_bad_module;
@@ -237,6 +243,104 @@ enum spectre_v2_mitigation_cmd {
SPECTRE_V2_CMD_RETPOLINE_AMD,
};
+enum spectre_v2_user_cmd {
+ SPECTRE_V2_USER_CMD_NONE,
+ SPECTRE_V2_USER_CMD_AUTO,
+ SPECTRE_V2_USER_CMD_FORCE,
+};
+
+static const char * const spectre_v2_user_strings[] = {
+ [SPECTRE_V2_USER_NONE] = "User space: Vulnerable",
+ [SPECTRE_V2_USER_STRICT] = "User space: Mitigation: STIBP protection",
+};
+
+static const struct {
+ const char *option;
+ enum spectre_v2_user_cmd cmd;
+ bool secure;
+} v2_user_options[] __initdata = {
+ { "auto", SPECTRE_V2_USER_CMD_AUTO, false },
+ { "off", SPECTRE_V2_USER_CMD_NONE, false },
+ { "on", SPECTRE_V2_USER_CMD_FORCE, true },
+};
+
+static void __init spec_v2_user_print_cond(const char *reason, bool secure)
+{
+ if (boot_cpu_has_bug(X86_BUG_SPECTRE_V2) != secure)
+ pr_info("spectre_v2_user=%s forced on command line.\n", reason);
+}
+
+static enum spectre_v2_user_cmd __init
+spectre_v2_parse_user_cmdline(enum spectre_v2_mitigation_cmd v2_cmd)
+{
+ char arg[20];
+ int ret, i;
+
+ switch (v2_cmd) {
+ case SPECTRE_V2_CMD_NONE:
+ return SPECTRE_V2_USER_CMD_NONE;
+ case SPECTRE_V2_CMD_FORCE:
+ return SPECTRE_V2_USER_CMD_FORCE;
+ default:
+ break;
+ }
+
+ ret = cmdline_find_option(boot_command_line, "spectre_v2_user",
+ arg, sizeof(arg));
+ if (ret < 0)
+ return SPECTRE_V2_USER_CMD_AUTO;
+
+ for (i = 0; i < ARRAY_SIZE(v2_user_options); i++) {
+ if (match_option(arg, ret, v2_user_options[i].option)) {
+ spec_v2_user_print_cond(v2_user_options[i].option,
+ v2_user_options[i].secure);
+ return v2_user_options[i].cmd;
+ }
+ }
+
+ pr_err("Unknown user space protection option (%s). Switching to AUTO select\n", arg);
+ return SPECTRE_V2_USER_CMD_AUTO;
+}
+
+static void __init
+spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
+{
+ enum spectre_v2_user_mitigation mode = SPECTRE_V2_USER_NONE;
+ bool smt_possible = IS_ENABLED(CONFIG_SMP);
+
+ if (!boot_cpu_has(X86_FEATURE_IBPB) && !boot_cpu_has(X86_FEATURE_STIBP))
+ return;
+
+ if (cpu_smt_control == CPU_SMT_FORCE_DISABLED ||
+ cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
+ 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;
+ }
+
+ /* Initialize Indirect Branch Prediction Barrier */
+ if (boot_cpu_has(X86_FEATURE_IBPB)) {
+ setup_force_cpu_cap(X86_FEATURE_USE_IBPB);
+ pr_info("Spectre v2 mitigation: Enabling Indirect Branch Prediction Barrier\n");
+ }
+
+ /* If enhanced IBRS is enabled no STIPB required */
+ if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
+ return;
+
+set_mode:
+ spectre_v2_user = mode;
+ /* Only print the STIBP mode when SMT possible */
+ if (smt_possible)
+ pr_info("%s\n", spectre_v2_user_strings[mode]);
+}
+
static const char * const spectre_v2_strings[] = {
[SPECTRE_V2_NONE] = "Vulnerable",
[SPECTRE_V2_RETPOLINE_GENERIC] = "Mitigation: Full generic retpoline",
@@ -385,12 +489,6 @@ specv2_set_mode:
setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW);
pr_info("Spectre v2 / SpectreRSB mitigation: Filling RSB on context switch\n");
- /* Initialize Indirect Branch Prediction Barrier if supported */
- if (boot_cpu_has(X86_FEATURE_IBPB)) {
- setup_force_cpu_cap(X86_FEATURE_USE_IBPB);
- pr_info("Spectre v2 mitigation: Enabling Indirect Branch Prediction Barrier\n");
- }
-
/*
* Retpoline means the kernel is safe because it has no indirect
* branches. Enhanced IBRS protects firmware too, so, enable restricted
@@ -407,23 +505,21 @@ specv2_set_mode:
pr_info("Enabling Restricted Speculation for firmware calls\n");
}
+ /* Set up IBPB and STIBP depending on the general spectre V2 command */
+ spectre_v2_user_select_mitigation(cmd);
+
/* Enable STIBP if appropriate */
arch_smt_update();
}
static bool stibp_needed(void)
{
- if (spectre_v2_enabled == SPECTRE_V2_NONE)
- return false;
-
/* Enhanced IBRS makes using STIBP unnecessary. */
if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
return false;
- if (!boot_cpu_has(X86_FEATURE_STIBP))
- return false;
-
- return true;
+ /* Check for strict user mitigation mode */
+ return spectre_v2_user == SPECTRE_V2_USER_STRICT;
}
static void update_stibp_msr(void *info)
@@ -844,10 +940,13 @@ static char *stibp_state(void)
if (spectre_v2_enabled == SPECTRE_V2_IBRS_ENHANCED)
return "";
- if (x86_spec_ctrl_base & SPEC_CTRL_STIBP)
- return ", STIBP";
- else
- return "";
+ switch (spectre_v2_user) {
+ case SPECTRE_V2_USER_NONE:
+ return ", STIBP: disabled";
+ case SPECTRE_V2_USER_STRICT:
+ return ", STIBP: forced";
+ }
+ return "";
}
static char *ibpb_state(void)
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