2018-12-13 23:05:41

by Tom Lendacky

[permalink] [raw]
Subject: [PATCH v3] x86/speculation: Add support for STIBP always-on preferred mode

Different AMD processors may have different implementations of STIBP.
When STIBP is conditionally enabled, some implementations would benefit
from having STIBP always on instead of toggling the STIBP bit through MSR
writes. This preference is advertised through a CPUID feature bit.

When conditional STIBP support is requested at boot and the CPU advertises
STIBP always-on mode as preferred, switch to STIBP "on" support. To show
that this transition has occurred, create a new spectre_v2_user_mitigation
value and a new spectre_v2_user_strings message. The new mitigation value
is used in spectre_v2_user_select_mitigation() to print the new mitigation
message as well as to return a new string from stibp_state().

Signed-off-by: Tom Lendacky <[email protected]>
---

This patch is against the x86/pti branch of the tip tree:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/pti

Changes from v2:
- Reverted back to original version of the patch
- Updated the messages that are issued. I'm not terribly happy with the
wording, so if there are any suggestions...

Changes from v1:
- Removed explicit SPECTRE_V2_USER_STRICT_PREFERRED mode
- Added a message when switching to always-on mode
- Set and used a static boolean for the string in stibp_state()

arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/include/asm/nospec-branch.h | 1 +
arch/x86/kernel/cpu/bugs.c | 28 ++++++++++++++++++++++------
3 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 28c4a50..df8e94e2 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -284,6 +284,7 @@
#define X86_FEATURE_AMD_IBPB (13*32+12) /* "" Indirect Branch Prediction Barrier */
#define X86_FEATURE_AMD_IBRS (13*32+14) /* "" Indirect Branch Restricted Speculation */
#define X86_FEATURE_AMD_STIBP (13*32+15) /* "" Single Thread Indirect Branch Predictors */
+#define X86_FEATURE_AMD_STIBP_ALWAYS_ON (13*32+17) /* "" Single Thread Indirect Branch Predictors always-on preferred */
#define X86_FEATURE_AMD_SSBD (13*32+24) /* "" Speculative Store Bypass Disable */
#define X86_FEATURE_VIRT_SSBD (13*32+25) /* Virtualized Speculative Store Bypass Disable */
#define X86_FEATURE_AMD_SSB_NO (13*32+26) /* "" Speculative Store Bypass is fixed in hardware. */
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 032b600..dad12b7 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -232,6 +232,7 @@ enum spectre_v2_mitigation {
enum spectre_v2_user_mitigation {
SPECTRE_V2_USER_NONE,
SPECTRE_V2_USER_STRICT,
+ SPECTRE_V2_USER_STRICT_PREFERRED,
SPECTRE_V2_USER_PRCTL,
SPECTRE_V2_USER_SECCOMP,
};
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 58689ac..77bf225 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -262,10 +262,11 @@ enum spectre_v2_user_cmd {
};

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",
- [SPECTRE_V2_USER_SECCOMP] = "User space: Mitigation: STIBP via seccomp and prctl",
+ [SPECTRE_V2_USER_NONE] = "User space: Vulnerable",
+ [SPECTRE_V2_USER_STRICT] = "User space: Mitigation: STIBP protection",
+ [SPECTRE_V2_USER_STRICT_PREFERRED] = "User space: Mitigation: STIBP always-on protection",
+ [SPECTRE_V2_USER_PRCTL] = "User space: Mitigation: STIBP via prctl",
+ [SPECTRE_V2_USER_SECCOMP] = "User space: Mitigation: STIBP via seccomp and prctl",
};

static const struct {
@@ -355,6 +356,15 @@ static void __init spec_v2_user_print_cond(const char *reason, bool secure)
break;
}

+ /*
+ * At this point, an STIBP mode other than "off" has been set.
+ * If STIBP support is not being forced, check if STIBP always-on
+ * is preferred.
+ */
+ if (mode != SPECTRE_V2_USER_STRICT &&
+ boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON))
+ mode = SPECTRE_V2_USER_STRICT_PREFERRED;
+
/* Initialize Indirect Branch Prediction Barrier */
if (boot_cpu_has(X86_FEATURE_IBPB)) {
setup_force_cpu_cap(X86_FEATURE_USE_IBPB);
@@ -610,6 +620,7 @@ void arch_smt_update(void)
case SPECTRE_V2_USER_NONE:
break;
case SPECTRE_V2_USER_STRICT:
+ case SPECTRE_V2_USER_STRICT_PREFERRED:
update_stibp_strict();
break;
case SPECTRE_V2_USER_PRCTL:
@@ -812,7 +823,8 @@ static int ib_prctl_set(struct task_struct *task, unsigned long ctrl)
* Indirect branch speculation is always disabled in strict
* mode.
*/
- if (spectre_v2_user == SPECTRE_V2_USER_STRICT)
+ if (spectre_v2_user == SPECTRE_V2_USER_STRICT ||
+ spectre_v2_user == SPECTRE_V2_USER_STRICT_PREFERRED)
return -EPERM;
task_clear_spec_ib_disable(task);
task_update_spec_tif(task);
@@ -825,7 +837,8 @@ static int ib_prctl_set(struct task_struct *task, unsigned long ctrl)
*/
if (spectre_v2_user == SPECTRE_V2_USER_NONE)
return -EPERM;
- if (spectre_v2_user == SPECTRE_V2_USER_STRICT)
+ if (spectre_v2_user == SPECTRE_V2_USER_STRICT ||
+ spectre_v2_user == SPECTRE_V2_USER_STRICT_PREFERRED)
return 0;
task_set_spec_ib_disable(task);
if (ctrl == PR_SPEC_FORCE_DISABLE)
@@ -896,6 +909,7 @@ static int ib_prctl_get(struct task_struct *task)
return PR_SPEC_PRCTL | PR_SPEC_DISABLE;
return PR_SPEC_PRCTL | PR_SPEC_ENABLE;
case SPECTRE_V2_USER_STRICT:
+ case SPECTRE_V2_USER_STRICT_PREFERRED:
return PR_SPEC_DISABLE;
default:
return PR_SPEC_NOT_AFFECTED;
@@ -1089,6 +1103,8 @@ static char *stibp_state(void)
return ", STIBP: disabled";
case SPECTRE_V2_USER_STRICT:
return ", STIBP: forced";
+ case SPECTRE_V2_USER_STRICT_PREFERRED:
+ return ", STIBP: always-on";
case SPECTRE_V2_USER_PRCTL:
case SPECTRE_V2_USER_SECCOMP:
if (static_key_enabled(&switch_to_cond_stibp))


2018-12-14 20:52:24

by Borislav Petkov

[permalink] [raw]
Subject: Re: [PATCH v3] x86/speculation: Add support for STIBP always-on preferred mode

On Thu, Dec 13, 2018 at 11:03:54PM +0000, Lendacky, Thomas wrote:
> Different AMD processors may have different implementations of STIBP.
> When STIBP is conditionally enabled, some implementations would benefit
> from having STIBP always on instead of toggling the STIBP bit through MSR
> writes. This preference is advertised through a CPUID feature bit.
>
> When conditional STIBP support is requested at boot and the CPU advertises
> STIBP always-on mode as preferred, switch to STIBP "on" support. To show
> that this transition has occurred, create a new spectre_v2_user_mitigation
> value and a new spectre_v2_user_strings message. The new mitigation value
> is used in spectre_v2_user_select_mitigation() to print the new mitigation
> message as well as to return a new string from stibp_state().
>
> Signed-off-by: Tom Lendacky <[email protected]>
> ---
>
> This patch is against the x86/pti branch of the tip tree:
> git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/pti
>
> Changes from v2:
> - Reverted back to original version of the patch
> - Updated the messages that are issued. I'm not terribly happy with the
> wording, so if there are any suggestions...
>
> Changes from v1:
> - Removed explicit SPECTRE_V2_USER_STRICT_PREFERRED mode
> - Added a message when switching to always-on mode
> - Set and used a static boolean for the string in stibp_state()
>
> arch/x86/include/asm/cpufeatures.h | 1 +
> arch/x86/include/asm/nospec-branch.h | 1 +
> arch/x86/kernel/cpu/bugs.c | 28 ++++++++++++++++++++++------
> 3 files changed, 24 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index 28c4a50..df8e94e2 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -284,6 +284,7 @@
> #define X86_FEATURE_AMD_IBPB (13*32+12) /* "" Indirect Branch Prediction Barrier */
> #define X86_FEATURE_AMD_IBRS (13*32+14) /* "" Indirect Branch Restricted Speculation */
> #define X86_FEATURE_AMD_STIBP (13*32+15) /* "" Single Thread Indirect Branch Predictors */
> +#define X86_FEATURE_AMD_STIBP_ALWAYS_ON (13*32+17) /* "" Single Thread Indirect Branch Predictors always-on preferred */
> #define X86_FEATURE_AMD_SSBD (13*32+24) /* "" Speculative Store Bypass Disable */
> #define X86_FEATURE_VIRT_SSBD (13*32+25) /* Virtualized Speculative Store Bypass Disable */
> #define X86_FEATURE_AMD_SSB_NO (13*32+26) /* "" Speculative Store Bypass is fixed in hardware. */
> diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
> index 032b600..dad12b7 100644
> --- a/arch/x86/include/asm/nospec-branch.h
> +++ b/arch/x86/include/asm/nospec-branch.h
> @@ -232,6 +232,7 @@ enum spectre_v2_mitigation {
> enum spectre_v2_user_mitigation {
> SPECTRE_V2_USER_NONE,
> SPECTRE_V2_USER_STRICT,
> + SPECTRE_V2_USER_STRICT_PREFERRED,
> SPECTRE_V2_USER_PRCTL,
> SPECTRE_V2_USER_SECCOMP,
> };
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 58689ac..77bf225 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -262,10 +262,11 @@ enum spectre_v2_user_cmd {
> };
>
> 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",
> - [SPECTRE_V2_USER_SECCOMP] = "User space: Mitigation: STIBP via seccomp and prctl",
> + [SPECTRE_V2_USER_NONE] = "User space: Vulnerable",
> + [SPECTRE_V2_USER_STRICT] = "User space: Mitigation: STIBP protection",
> + [SPECTRE_V2_USER_STRICT_PREFERRED] = "User space: Mitigation: STIBP always-on protection",

Barring the "preferred" vs "always-on" bikeshed controversy :-P, I don't
see anything wrong with this version.

The only thing that could be improved maybe is having the mode name
and the user visible string match for ease of code staring during bug
hunting...

--
Regards/Gruss,
Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

Subject: [tip:x86/pti] x86/speculation: Add support for STIBP always-on preferred mode

Commit-ID: bbec2eb92c567938b0182a8534e7421f64fbd56d
Gitweb: https://git.kernel.org/tip/bbec2eb92c567938b0182a8534e7421f64fbd56d
Author: LendackyThomas <[email protected]>
AuthorDate: Thu, 13 Dec 2018 23:03:54 +0000
Committer: Thomas Gleixner <[email protected]>
CommitDate: Tue, 18 Dec 2018 13:36:53 +0100

x86/speculation: Add support for STIBP always-on preferred mode

Different AMD processors may have different implementations of STIBP.
When STIBP is conditionally enabled, some implementations would benefit
from having STIBP always on instead of toggling the STIBP bit through MSR
writes. This preference is advertised through a CPUID feature bit.

When conditional STIBP support is requested at boot and the CPU advertises
STIBP always-on mode as preferred, switch to STIBP "on" support. To show
that this transition has occurred, create a new spectre_v2_user_mitigation
value and a new spectre_v2_user_strings message. The new mitigation value
is used in spectre_v2_user_select_mitigation() to print the new mitigation
message as well as to return a new string from stibp_state().

Signed-off-by: Tom Lendacky <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Jiri Kosina <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Tim Chen <[email protected]>
Cc: David Woodhouse <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

---
arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/include/asm/nospec-branch.h | 1 +
arch/x86/kernel/cpu/bugs.c | 28 ++++++++++++++++++++++------
3 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 28c4a502b419..df8e94e2f7be 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -284,6 +284,7 @@
#define X86_FEATURE_AMD_IBPB (13*32+12) /* "" Indirect Branch Prediction Barrier */
#define X86_FEATURE_AMD_IBRS (13*32+14) /* "" Indirect Branch Restricted Speculation */
#define X86_FEATURE_AMD_STIBP (13*32+15) /* "" Single Thread Indirect Branch Predictors */
+#define X86_FEATURE_AMD_STIBP_ALWAYS_ON (13*32+17) /* "" Single Thread Indirect Branch Predictors always-on preferred */
#define X86_FEATURE_AMD_SSBD (13*32+24) /* "" Speculative Store Bypass Disable */
#define X86_FEATURE_VIRT_SSBD (13*32+25) /* Virtualized Speculative Store Bypass Disable */
#define X86_FEATURE_AMD_SSB_NO (13*32+26) /* "" Speculative Store Bypass is fixed in hardware. */
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 032b6009baab..dad12b767ba0 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -232,6 +232,7 @@ enum spectre_v2_mitigation {
enum spectre_v2_user_mitigation {
SPECTRE_V2_USER_NONE,
SPECTRE_V2_USER_STRICT,
+ SPECTRE_V2_USER_STRICT_PREFERRED,
SPECTRE_V2_USER_PRCTL,
SPECTRE_V2_USER_SECCOMP,
};
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 58689ac64440..77bf22546ddd 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -262,10 +262,11 @@ enum spectre_v2_user_cmd {
};

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",
- [SPECTRE_V2_USER_SECCOMP] = "User space: Mitigation: STIBP via seccomp and prctl",
+ [SPECTRE_V2_USER_NONE] = "User space: Vulnerable",
+ [SPECTRE_V2_USER_STRICT] = "User space: Mitigation: STIBP protection",
+ [SPECTRE_V2_USER_STRICT_PREFERRED] = "User space: Mitigation: STIBP always-on protection",
+ [SPECTRE_V2_USER_PRCTL] = "User space: Mitigation: STIBP via prctl",
+ [SPECTRE_V2_USER_SECCOMP] = "User space: Mitigation: STIBP via seccomp and prctl",
};

static const struct {
@@ -355,6 +356,15 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
break;
}

+ /*
+ * At this point, an STIBP mode other than "off" has been set.
+ * If STIBP support is not being forced, check if STIBP always-on
+ * is preferred.
+ */
+ if (mode != SPECTRE_V2_USER_STRICT &&
+ boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON))
+ mode = SPECTRE_V2_USER_STRICT_PREFERRED;
+
/* Initialize Indirect Branch Prediction Barrier */
if (boot_cpu_has(X86_FEATURE_IBPB)) {
setup_force_cpu_cap(X86_FEATURE_USE_IBPB);
@@ -610,6 +620,7 @@ void arch_smt_update(void)
case SPECTRE_V2_USER_NONE:
break;
case SPECTRE_V2_USER_STRICT:
+ case SPECTRE_V2_USER_STRICT_PREFERRED:
update_stibp_strict();
break;
case SPECTRE_V2_USER_PRCTL:
@@ -812,7 +823,8 @@ static int ib_prctl_set(struct task_struct *task, unsigned long ctrl)
* Indirect branch speculation is always disabled in strict
* mode.
*/
- if (spectre_v2_user == SPECTRE_V2_USER_STRICT)
+ if (spectre_v2_user == SPECTRE_V2_USER_STRICT ||
+ spectre_v2_user == SPECTRE_V2_USER_STRICT_PREFERRED)
return -EPERM;
task_clear_spec_ib_disable(task);
task_update_spec_tif(task);
@@ -825,7 +837,8 @@ static int ib_prctl_set(struct task_struct *task, unsigned long ctrl)
*/
if (spectre_v2_user == SPECTRE_V2_USER_NONE)
return -EPERM;
- if (spectre_v2_user == SPECTRE_V2_USER_STRICT)
+ if (spectre_v2_user == SPECTRE_V2_USER_STRICT ||
+ spectre_v2_user == SPECTRE_V2_USER_STRICT_PREFERRED)
return 0;
task_set_spec_ib_disable(task);
if (ctrl == PR_SPEC_FORCE_DISABLE)
@@ -896,6 +909,7 @@ static int ib_prctl_get(struct task_struct *task)
return PR_SPEC_PRCTL | PR_SPEC_DISABLE;
return PR_SPEC_PRCTL | PR_SPEC_ENABLE;
case SPECTRE_V2_USER_STRICT:
+ case SPECTRE_V2_USER_STRICT_PREFERRED:
return PR_SPEC_DISABLE;
default:
return PR_SPEC_NOT_AFFECTED;
@@ -1089,6 +1103,8 @@ static char *stibp_state(void)
return ", STIBP: disabled";
case SPECTRE_V2_USER_STRICT:
return ", STIBP: forced";
+ case SPECTRE_V2_USER_STRICT_PREFERRED:
+ return ", STIBP: always-on";
case SPECTRE_V2_USER_PRCTL:
case SPECTRE_V2_USER_SECCOMP:
if (static_key_enabled(&switch_to_cond_stibp))

Subject: [tip:x86/pti] x86/speculation: Add support for STIBP always-on preferred mode

Commit-ID: 20c3a2c33e9fdc82e9e8e8d2a6445b3256d20191
Gitweb: https://git.kernel.org/tip/20c3a2c33e9fdc82e9e8e8d2a6445b3256d20191
Author: Thomas Lendacky <[email protected]>
AuthorDate: Thu, 13 Dec 2018 23:03:54 +0000
Committer: Thomas Gleixner <[email protected]>
CommitDate: Tue, 18 Dec 2018 14:13:33 +0100

x86/speculation: Add support for STIBP always-on preferred mode

Different AMD processors may have different implementations of STIBP.
When STIBP is conditionally enabled, some implementations would benefit
from having STIBP always on instead of toggling the STIBP bit through MSR
writes. This preference is advertised through a CPUID feature bit.

When conditional STIBP support is requested at boot and the CPU advertises
STIBP always-on mode as preferred, switch to STIBP "on" support. To show
that this transition has occurred, create a new spectre_v2_user_mitigation
value and a new spectre_v2_user_strings message. The new mitigation value
is used in spectre_v2_user_select_mitigation() to print the new mitigation
message as well as to return a new string from stibp_state().

Signed-off-by: Tom Lendacky <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Jiri Kosina <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Tim Chen <[email protected]>
Cc: David Woodhouse <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

---
arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/include/asm/nospec-branch.h | 1 +
arch/x86/kernel/cpu/bugs.c | 28 ++++++++++++++++++++++------
3 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 28c4a502b419..df8e94e2f7be 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -284,6 +284,7 @@
#define X86_FEATURE_AMD_IBPB (13*32+12) /* "" Indirect Branch Prediction Barrier */
#define X86_FEATURE_AMD_IBRS (13*32+14) /* "" Indirect Branch Restricted Speculation */
#define X86_FEATURE_AMD_STIBP (13*32+15) /* "" Single Thread Indirect Branch Predictors */
+#define X86_FEATURE_AMD_STIBP_ALWAYS_ON (13*32+17) /* "" Single Thread Indirect Branch Predictors always-on preferred */
#define X86_FEATURE_AMD_SSBD (13*32+24) /* "" Speculative Store Bypass Disable */
#define X86_FEATURE_VIRT_SSBD (13*32+25) /* Virtualized Speculative Store Bypass Disable */
#define X86_FEATURE_AMD_SSB_NO (13*32+26) /* "" Speculative Store Bypass is fixed in hardware. */
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 032b6009baab..dad12b767ba0 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -232,6 +232,7 @@ enum spectre_v2_mitigation {
enum spectre_v2_user_mitigation {
SPECTRE_V2_USER_NONE,
SPECTRE_V2_USER_STRICT,
+ SPECTRE_V2_USER_STRICT_PREFERRED,
SPECTRE_V2_USER_PRCTL,
SPECTRE_V2_USER_SECCOMP,
};
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 58689ac64440..77bf22546ddd 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -262,10 +262,11 @@ enum spectre_v2_user_cmd {
};

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",
- [SPECTRE_V2_USER_SECCOMP] = "User space: Mitigation: STIBP via seccomp and prctl",
+ [SPECTRE_V2_USER_NONE] = "User space: Vulnerable",
+ [SPECTRE_V2_USER_STRICT] = "User space: Mitigation: STIBP protection",
+ [SPECTRE_V2_USER_STRICT_PREFERRED] = "User space: Mitigation: STIBP always-on protection",
+ [SPECTRE_V2_USER_PRCTL] = "User space: Mitigation: STIBP via prctl",
+ [SPECTRE_V2_USER_SECCOMP] = "User space: Mitigation: STIBP via seccomp and prctl",
};

static const struct {
@@ -355,6 +356,15 @@ spectre_v2_user_select_mitigation(enum spectre_v2_mitigation_cmd v2_cmd)
break;
}

+ /*
+ * At this point, an STIBP mode other than "off" has been set.
+ * If STIBP support is not being forced, check if STIBP always-on
+ * is preferred.
+ */
+ if (mode != SPECTRE_V2_USER_STRICT &&
+ boot_cpu_has(X86_FEATURE_AMD_STIBP_ALWAYS_ON))
+ mode = SPECTRE_V2_USER_STRICT_PREFERRED;
+
/* Initialize Indirect Branch Prediction Barrier */
if (boot_cpu_has(X86_FEATURE_IBPB)) {
setup_force_cpu_cap(X86_FEATURE_USE_IBPB);
@@ -610,6 +620,7 @@ void arch_smt_update(void)
case SPECTRE_V2_USER_NONE:
break;
case SPECTRE_V2_USER_STRICT:
+ case SPECTRE_V2_USER_STRICT_PREFERRED:
update_stibp_strict();
break;
case SPECTRE_V2_USER_PRCTL:
@@ -812,7 +823,8 @@ static int ib_prctl_set(struct task_struct *task, unsigned long ctrl)
* Indirect branch speculation is always disabled in strict
* mode.
*/
- if (spectre_v2_user == SPECTRE_V2_USER_STRICT)
+ if (spectre_v2_user == SPECTRE_V2_USER_STRICT ||
+ spectre_v2_user == SPECTRE_V2_USER_STRICT_PREFERRED)
return -EPERM;
task_clear_spec_ib_disable(task);
task_update_spec_tif(task);
@@ -825,7 +837,8 @@ static int ib_prctl_set(struct task_struct *task, unsigned long ctrl)
*/
if (spectre_v2_user == SPECTRE_V2_USER_NONE)
return -EPERM;
- if (spectre_v2_user == SPECTRE_V2_USER_STRICT)
+ if (spectre_v2_user == SPECTRE_V2_USER_STRICT ||
+ spectre_v2_user == SPECTRE_V2_USER_STRICT_PREFERRED)
return 0;
task_set_spec_ib_disable(task);
if (ctrl == PR_SPEC_FORCE_DISABLE)
@@ -896,6 +909,7 @@ static int ib_prctl_get(struct task_struct *task)
return PR_SPEC_PRCTL | PR_SPEC_DISABLE;
return PR_SPEC_PRCTL | PR_SPEC_ENABLE;
case SPECTRE_V2_USER_STRICT:
+ case SPECTRE_V2_USER_STRICT_PREFERRED:
return PR_SPEC_DISABLE;
default:
return PR_SPEC_NOT_AFFECTED;
@@ -1089,6 +1103,8 @@ static char *stibp_state(void)
return ", STIBP: disabled";
case SPECTRE_V2_USER_STRICT:
return ", STIBP: forced";
+ case SPECTRE_V2_USER_STRICT_PREFERRED:
+ return ", STIBP: always-on";
case SPECTRE_V2_USER_PRCTL:
case SPECTRE_V2_USER_SECCOMP:
if (static_key_enabled(&switch_to_cond_stibp))