2022-08-05 09:24:43

by Liu Song

Subject: [PATCH] arm64: spectre: increase parameters that can be used to turn off bhb mitigation individually

From: Liu Song <[email protected]>

In our environment, it was found that the mitigation BHB has a great
impact on the benchmark performance. For example, in the lmbench test,
the "process fork && exit" test performance drops by 20%.
So it is necessary to have the ability to turn off the mitigation
individually through cmdline, thus avoiding having to compile the
kernel by adjusting the config.

Signed-off-by: Liu Song <[email protected]>
---
arch/arm64/kernel/proton-pack.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
index 40be3a7..bd16903 100644
--- a/arch/arm64/kernel/proton-pack.c
+++ b/arch/arm64/kernel/proton-pack.c
@@ -988,6 +988,14 @@ static void this_cpu_set_vectors(enum arm64_bp_harden_el1_vectors slot)
isb();
}

+static bool __read_mostly __nospectre_bhb;
+static int __init parse_spectre_bhb_param(char *str)
+{
+ __nospectre_bhb = true;
+ return 0;
+}
+early_param("nospectre_bhb", parse_spectre_bhb_param);
+
void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry)
{
bp_hardening_cb_t cpu_cb;
@@ -1001,7 +1009,7 @@ void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry)
/* No point mitigating Spectre-BHB alone. */
} else if (!IS_ENABLED(CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY)) {
pr_info_once("spectre-bhb mitigation disabled by compile time option\n");
- } else if (cpu_mitigations_off()) {
+ } else if (cpu_mitigations_off() || __nospectre_bhb) {
pr_info_once("spectre-bhb mitigation disabled by command line option\n");
} else if (supports_ecbhb(SCOPE_LOCAL_CPU)) {
state = SPECTRE_MITIGATED;
--
1.8.3.1

2022-08-25 15:44:27

by Liu Song

Subject: Re: [PATCH] arm64: spectre: increase parameters that can be used to turn off bhb mitigation individually

Hi,

Is there any potential problem with this modification? Looking forward
to your reply.

Thanks

> From: Liu Song <[email protected]>
>
> In our environment, it was found that the mitigation BHB has a great
> impact on the benchmark performance. For example, in the lmbench test,
> the "process fork && exit" test performance drops by 20%.
> So it is necessary to have the ability to turn off the mitigation
> individually through cmdline, thus avoiding having to compile the
> kernel by adjusting the config.
>
> Signed-off-by: Liu Song <[email protected]>
> ---
> arch/arm64/kernel/proton-pack.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
> index 40be3a7..bd16903 100644
> --- a/arch/arm64/kernel/proton-pack.c
> +++ b/arch/arm64/kernel/proton-pack.c
> @@ -988,6 +988,14 @@ static void this_cpu_set_vectors(enum arm64_bp_harden_el1_vectors slot)
> isb();
> }
>
> +static bool __read_mostly __nospectre_bhb;
> +static int __init parse_spectre_bhb_param(char *str)
> +{
> + __nospectre_bhb = true;
> + return 0;
> +}
> +early_param("nospectre_bhb", parse_spectre_bhb_param);
> +
> void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry)
> {
> bp_hardening_cb_t cpu_cb;
> @@ -1001,7 +1009,7 @@ void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry)
> /* No point mitigating Spectre-BHB alone. */
> } else if (!IS_ENABLED(CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY)) {
> pr_info_once("spectre-bhb mitigation disabled by compile time option\n");
> - } else if (cpu_mitigations_off()) {
> + } else if (cpu_mitigations_off() || __nospectre_bhb) {
> pr_info_once("spectre-bhb mitigation disabled by command line option\n");
> } else if (supports_ecbhb(SCOPE_LOCAL_CPU)) {
> state = SPECTRE_MITIGATED;

2022-08-26 10:59:55

by Will Deacon

Subject: Re: [PATCH] arm64: spectre: increase parameters that can be used to turn off bhb mitigation individually

On Fri, Aug 05, 2022 at 05:21:14PM +0800, Liu Song wrote:
> From: Liu Song <[email protected]>
>
> In our environment, it was found that the mitigation BHB has a great
> impact on the benchmark performance. For example, in the lmbench test,
> the "process fork && exit" test performance drops by 20%.
> So it is necessary to have the ability to turn off the mitigation
> individually through cmdline, thus avoiding having to compile the
> kernel by adjusting the config.
>
> Signed-off-by: Liu Song <[email protected]>
> ---
> arch/arm64/kernel/proton-pack.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
> index 40be3a7..bd16903 100644
> --- a/arch/arm64/kernel/proton-pack.c
> +++ b/arch/arm64/kernel/proton-pack.c
> @@ -988,6 +988,14 @@ static void this_cpu_set_vectors(enum arm64_bp_harden_el1_vectors slot)
> isb();
> }
>
> +static bool __read_mostly __nospectre_bhb;
> +static int __init parse_spectre_bhb_param(char *str)
> +{
> + __nospectre_bhb = true;
> + return 0;
> +}
> +early_param("nospectre_bhb", parse_spectre_bhb_param);
> +
> void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry)
> {
> bp_hardening_cb_t cpu_cb;
> @@ -1001,7 +1009,7 @@ void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry)
> /* No point mitigating Spectre-BHB alone. */
> } else if (!IS_ENABLED(CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY)) {
> pr_info_once("spectre-bhb mitigation disabled by compile time option\n");
> - } else if (cpu_mitigations_off()) {
> + } else if (cpu_mitigations_off() || __nospectre_bhb) {
> pr_info_once("spectre-bhb mitigation disabled by command line option\n");
> } else if (supports_ecbhb(SCOPE_LOCAL_CPU)) {
> state = SPECTRE_MITIGATED;

It would be good to have an Ack (or a shrug) from somebody @arm.com on this
one.

Other than that, the documentation needs updating for the new option.

Will

2022-08-26 11:33:50

by Liu Song

Subject: Re: [PATCH] arm64: spectre: increase parameters that can be used to turn off bhb mitigation individually

> On Fri, Aug 05, 2022 at 05:21:14PM +0800, Liu Song wrote:
>> From: Liu Song <[email protected]>
>>
>> In our environment, it was found that the mitigation BHB has a great
>> impact on the benchmark performance. For example, in the lmbench test,
>> the "process fork && exit" test performance drops by 20%.
>> So it is necessary to have the ability to turn off the mitigation
>> individually through cmdline, thus avoiding having to compile the
>> kernel by adjusting the config.
>>
>> Signed-off-by: Liu Song <[email protected]>
>> ---
>> arch/arm64/kernel/proton-pack.c | 10 +++++++++-
>> 1 file changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
>> index 40be3a7..bd16903 100644
>> --- a/arch/arm64/kernel/proton-pack.c
>> +++ b/arch/arm64/kernel/proton-pack.c
>> @@ -988,6 +988,14 @@ static void this_cpu_set_vectors(enum arm64_bp_harden_el1_vectors slot)
>> isb();
>> }
>>
>> +static bool __read_mostly __nospectre_bhb;
>> +static int __init parse_spectre_bhb_param(char *str)
>> +{
>> + __nospectre_bhb = true;
>> + return 0;
>> +}
>> +early_param("nospectre_bhb", parse_spectre_bhb_param);
>> +
>> void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry)
>> {
>> bp_hardening_cb_t cpu_cb;
>> @@ -1001,7 +1009,7 @@ void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry)
>> /* No point mitigating Spectre-BHB alone. */
>> } else if (!IS_ENABLED(CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY)) {
>> pr_info_once("spectre-bhb mitigation disabled by compile time option\n");
>> - } else if (cpu_mitigations_off()) {
>> + } else if (cpu_mitigations_off() || __nospectre_bhb) {
>> pr_info_once("spectre-bhb mitigation disabled by command line option\n");
>> } else if (supports_ecbhb(SCOPE_LOCAL_CPU)) {
>> state = SPECTRE_MITIGATED;
> It would be good to have an Ack (or a shrug) from somebody @arm.com on this
> one.
>
> Other than that, the documentation needs updating for the new option.

Thanks for the reminder, I will post another V2 version.


Thanks


>
> Will

2022-08-26 13:05:57

by Liu Song

Subject: [PATCH v2] arm64: spectre: increase parameters that can be used to turn off bhb mitigation individually

From: Liu Song <[email protected]>

In our environment, it was found that the mitigation BHB has a great
impact on the benchmark performance. For example, in the lmbench test,
the "process fork && exit" test performance drops by 20%.
So it is necessary to have the ability to turn off the mitigation
individually through cmdline, thus avoiding having to compile the
kernel by adjusting the config.

Signed-off-by: Liu Song <[email protected]>
---
Documentation/admin-guide/kernel-parameters.txt | 5 +++++
arch/arm64/kernel/proton-pack.c | 10 +++++++++-
2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index d7f3090..1edc9a6 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3207,6 +3207,7 @@
spectre_v2_user=off [X86]
spec_store_bypass_disable=off [X86,PPC]
ssbd=force-off [ARM64]
+ nospectre_bhb [ARM64]
l1tf=off [X86]
mds=off [X86]
tsx_async_abort=off [X86]
@@ -3631,6 +3632,10 @@
vulnerability. System may allow data leaks with this
option.

+ nospectre_bhb [ARM64] Disable all mitigations for Spectre-BHB (branch
+ history injection) vulnerability. System may allow data leaks
+ with this option.
+
nospec_store_bypass_disable
[HW] Disable all mitigations for the Speculative Store Bypass vulnerability

diff --git a/arch/arm64/kernel/proton-pack.c b/arch/arm64/kernel/proton-pack.c
index 40be3a7..bd16903 100644
--- a/arch/arm64/kernel/proton-pack.c
+++ b/arch/arm64/kernel/proton-pack.c
@@ -988,6 +988,14 @@ static void this_cpu_set_vectors(enum arm64_bp_harden_el1_vectors slot)
isb();
}

+static bool __read_mostly __nospectre_bhb;
+static int __init parse_spectre_bhb_param(char *str)
+{
+ __nospectre_bhb = true;
+ return 0;
+}
+early_param("nospectre_bhb", parse_spectre_bhb_param);
+
void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry)
{
bp_hardening_cb_t cpu_cb;
@@ -1001,7 +1009,7 @@ void spectre_bhb_enable_mitigation(const struct arm64_cpu_capabilities *entry)
/* No point mitigating Spectre-BHB alone. */
} else if (!IS_ENABLED(CONFIG_MITIGATE_SPECTRE_BRANCH_HISTORY)) {
pr_info_once("spectre-bhb mitigation disabled by compile time option\n");
- } else if (cpu_mitigations_off()) {
+ } else if (cpu_mitigations_off() || __nospectre_bhb) {
pr_info_once("spectre-bhb mitigation disabled by command line option\n");
} else if (supports_ecbhb(SCOPE_LOCAL_CPU)) {
state = SPECTRE_MITIGATED;
--
1.8.3.1