From: Kees Cook <keescook@chromium.org>
Date: Thu, 3 May 2018 14:37:54 -0700
Subject: x86/speculation: Make "seccomp" the default mode for Speculative Store Bypass
Patch-mainline: v4.17-rc7
Git-commit: f21b53b20c754021935ea43364dbf53778eeba32
References: bsc#1087082 CVE-2018-3639
Unless explicitly opted out of, anything running under seccomp will have
SSB mitigations enabled. Choosing the "prctl" mode will disable this.
[ tglx: Adjusted it to the new arch_seccomp_spec_mitigate() mechanism ]
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Borislav Petkov <bp@suse.de>
---
Documentation/admin-guide/kernel-parameters.txt | 26 ++++++++++++-------
arch/x86/include/asm/nospec-branch.h | 1
arch/x86/kernel/cpu/bugs.c | 32 +++++++++++++++++-------
3 files changed, 41 insertions(+), 18 deletions(-)
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -230,6 +230,7 @@ enum ssb_mitigation {
SPEC_STORE_BYPASS_NONE,
SPEC_STORE_BYPASS_DISABLE,
SPEC_STORE_BYPASS_PRCTL,
+ SPEC_STORE_BYPASS_SECCOMP,
};
extern char __indirect_thunk_start[];
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -434,22 +434,25 @@ enum ssb_mitigation_cmd {
SPEC_STORE_BYPASS_CMD_AUTO,
SPEC_STORE_BYPASS_CMD_ON,
SPEC_STORE_BYPASS_CMD_PRCTL,
+ SPEC_STORE_BYPASS_CMD_SECCOMP,
};
static const char *ssb_strings[] = {
[SPEC_STORE_BYPASS_NONE] = "Vulnerable",
[SPEC_STORE_BYPASS_DISABLE] = "Mitigation: Speculative Store Bypass disabled",
- [SPEC_STORE_BYPASS_PRCTL] = "Mitigation: Speculative Store Bypass disabled via prctl"
+ [SPEC_STORE_BYPASS_PRCTL] = "Mitigation: Speculative Store Bypass disabled via prctl",
+ [SPEC_STORE_BYPASS_SECCOMP] = "Mitigation: Speculative Store Bypass disabled via prctl and seccomp",
};
static const struct {
const char *option;
enum ssb_mitigation_cmd cmd;
} ssb_mitigation_options[] = {
- { "auto", SPEC_STORE_BYPASS_CMD_AUTO }, /* Platform decides */
- { "on", SPEC_STORE_BYPASS_CMD_ON }, /* Disable Speculative Store Bypass */
- { "off", SPEC_STORE_BYPASS_CMD_NONE }, /* Don't touch Speculative Store Bypass */
- { "prctl", SPEC_STORE_BYPASS_CMD_PRCTL }, /* Disable Speculative Store Bypass via prctl */
+ { "auto", SPEC_STORE_BYPASS_CMD_AUTO }, /* Platform decides */
+ { "on", SPEC_STORE_BYPASS_CMD_ON }, /* Disable Speculative Store Bypass */
+ { "off", SPEC_STORE_BYPASS_CMD_NONE }, /* Don't touch Speculative Store Bypass */
+ { "prctl", SPEC_STORE_BYPASS_CMD_PRCTL }, /* Disable Speculative Store Bypass via prctl */
+ { "seccomp", SPEC_STORE_BYPASS_CMD_SECCOMP }, /* Disable Speculative Store Bypass via prctl and seccomp */
};
static enum ssb_mitigation_cmd __init ssb_parse_cmdline(void)
@@ -499,8 +502,15 @@ static enum ssb_mitigation_cmd __init __
switch (cmd) {
case SPEC_STORE_BYPASS_CMD_AUTO:
- /* Choose prctl as the default mode */
- mode = SPEC_STORE_BYPASS_PRCTL;
+ case SPEC_STORE_BYPASS_CMD_SECCOMP:
+ /*
+ * Choose prctl+seccomp as the default mode if seccomp is
+ * enabled.
+ */
+ if (IS_ENABLED(CONFIG_SECCOMP))
+ mode = SPEC_STORE_BYPASS_SECCOMP;
+ else
+ mode = SPEC_STORE_BYPASS_PRCTL;
break;
case SPEC_STORE_BYPASS_CMD_ON:
mode = SPEC_STORE_BYPASS_DISABLE;
@@ -548,12 +558,14 @@ static void ssb_select_mitigation()
}
#undef pr_fmt
+#define pr_fmt(fmt) "Speculation prctl: " fmt
static int ssb_prctl_set(struct task_struct *task, unsigned long ctrl)
{
bool update;
- if (ssb_mode != SPEC_STORE_BYPASS_PRCTL)
+ if (ssb_mode != SPEC_STORE_BYPASS_PRCTL &&
+ ssb_mode != SPEC_STORE_BYPASS_SECCOMP)
return -ENXIO;
switch (ctrl) {
@@ -601,7 +613,8 @@ int arch_prctl_spec_ctrl_set(struct task
#ifdef CONFIG_SECCOMP
void arch_seccomp_spec_mitigate(struct task_struct *task)
{
- ssb_prctl_set(task, PR_SPEC_FORCE_DISABLE);
+ if (ssb_mode == SPEC_STORE_BYPASS_SECCOMP)
+ ssb_prctl_set(task, PR_SPEC_FORCE_DISABLE);
}
#endif
@@ -610,6 +623,7 @@ static int ssb_prctl_get(struct task_str
switch (ssb_mode) {
case SPEC_STORE_BYPASS_DISABLE:
return PR_SPEC_DISABLE;
+ case SPEC_STORE_BYPASS_SECCOMP:
case SPEC_STORE_BYPASS_PRCTL:
if (task_spec_ssb_force_disable(task))
return PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE;
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3928,19 +3928,27 @@
This parameter controls whether the Speculative Store
Bypass optimization is used.
- on - Unconditionally disable Speculative Store Bypass
- off - Unconditionally enable Speculative Store Bypass
- auto - Kernel detects whether the CPU model contains an
- implementation of Speculative Store Bypass and
- picks the most appropriate mitigation.
- prctl - Control Speculative Store Bypass per thread
- via prctl. Speculative Store Bypass is enabled
- for a process by default. The state of the control
- is inherited on fork.
+ on - Unconditionally disable Speculative Store Bypass
+ off - Unconditionally enable Speculative Store Bypass
+ auto - Kernel detects whether the CPU model contains an
+ implementation of Speculative Store Bypass and
+ picks the most appropriate mitigation. If the
+ CPU is not vulnerable, "off" is selected. If the
+ CPU is vulnerable the default mitigation is
+ architecture and Kconfig dependent. See below.
+ prctl - Control Speculative Store Bypass per thread
+ via prctl. Speculative Store Bypass is enabled
+ for a process by default. The state of the control
+ is inherited on fork.
+ seccomp - Same as "prctl" above, but all seccomp threads
+ will disable SSB unless they explicitly opt out.
Not specifying this option is equivalent to
spec_store_bypass_disable=auto.
+ Default mitigations:
+ X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
+
spia_io_base= [HW,MTD]
spia_fio_base=
spia_pedr=