Re: [PATCH RFC 5/5] arm64/speculation: Add support for 'cpu_spec_mitigations=' cmdline options

Steven Price
2019-04-05T14:39:58Z

On 04/04/2019 17:44, Josh Poimboeuf wrote:
> Configure arm64 runtime CPU speculation bug mitigations in accordance
> with the 'cpu_spec_mitigations=' cmdline options. This affects
> Meltdown and Speculative Store Bypass.
>
> The default behavior is unchanged.
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> ---
> Documentation/admin-guide/kernel-parameters.txt | 2 ++
> arch/arm64/kernel/cpu_errata.c | 4 ++++
> arch/arm64/kernel/cpufeature.c | 6 ++++++
> 3 files changed, 12 insertions(+)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index e838af96daa4..0b54385ee7a8 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2553,11 +2553,13 @@
> off
> Disable all speculative CPU mitigations.
> Equivalent to: nopti [x86, powerpc]
> + kpti=0 [arm64]
> nospectre_v1 [powerpc]
> nospectre_v2 [x86, powerpc, s390]
> spectre_v2_user=off [x86]
> nobp=0 [s390]
> spec_store_bypass_disable=off [x86, powerpc]
> + ssbd=force-off [arm64]
> l1tf=off [x86]
>
> auto (default)
> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> index 9950bb0cbd52..db8d27e3fb1c 100644
> --- a/arch/arm64/kernel/cpu_errata.c
> +++ b/arch/arm64/kernel/cpu_errata.c
> @@ -19,6 +19,7 @@
> #include <linux/arm-smccc.h>
> #include <linux/psci.h>
> #include <linux/types.h>
> +#include <linux/cpu.h>
> #include <asm/cpu.h>
> #include <asm/cputype.h>
> #include <asm/cpufeature.h>
> @@ -385,6 +386,9 @@ static bool has_ssbd_mitigation(const struct arm64_cpu_capabilities *entry,
> return false;
> }
>
> + if (cpu_spec_mitigations == CPU_SPEC_MITIGATIONS_OFF)
> + ssbd_state = ARM64_SSBD_FORCE_DISABLE;
> +
> switch (psci_ops.conduit) {
> case PSCI_CONDUIT_HVC:
> arm_smccc_1_1_hvc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 4061de10cea6..4512b582d50f 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -25,6 +25,7 @@
> #include <linux/stop_machine.h>
> #include <linux/types.h>
> #include <linux/mm.h>
> +#include <linux/cpu.h>
> #include <asm/cpu.h>
> #include <asm/cpufeature.h>
> #include <asm/cpu_ops.h>
> @@ -978,6 +979,11 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
> __kpti_forced = -1;
> }
>
> + if (cpu_spec_mitigations == CPU_SPEC_MITIGATIONS_OFF) {
> + str = "cpu_spec_mitigations=off";

Might also be worth changing the initialisation of str, currently it is:

> char const *str = "command line option";

But now we have two command line options, perhaps "kpti command line
option".

Steve

> + __kpti_forced = -1;
> + }
> +
> /* Forced? */
> if (__kpti_forced) {
> pr_info_once("kernel page table isolation forced %s by %s\n",
>