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

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

[Liu Song]

From: Liu Song <liusong@linux.alibaba.com>

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 <liusong@linux.alibaba.com>
---
 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

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

[Liu Song]

Hi,

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

Thanks

> From: Liu Song <liusong@linux.alibaba.com>
>
> 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 <liusong@linux.alibaba.com>
> ---
>   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;

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

[Will Deacon]

On Fri, Aug 05, 2022 at 05:21:14PM +0800, Liu Song wrote:
> From: Liu Song <liusong@linux.alibaba.com>
> 
> 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 <liusong@linux.alibaba.com>
> ---
>  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

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

[Liu Song]

> On Fri, Aug 05, 2022 at 05:21:14PM +0800, Liu Song wrote:
>> From: Liu Song <liusong@linux.alibaba.com>
>>
>> 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 <liusong@linux.alibaba.com>
>> ---
>>   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

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

[Liu Song]

From: Liu Song <liusong@linux.alibaba.com>

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 <liusong@linux.alibaba.com>
---
 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