[PATCH 09/14] ARM: spectre-v2: add PSCI based hardening

[marc.zyngier@arm.com (Marc Zyngier)]

On Tue, 22 May 2018 18:57:18 +0100,
Russell King wrote:
> 
> On Tue, May 22, 2018 at 06:24:13PM +0100, Marc Zyngier wrote:
> > On 21/05/18 12:45, Russell King wrote:
> > > Add PSCI based hardening for cores that require more complex handling in
> > > firmware.
> > > 
> > > Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
> > > Acked-by: Marc Zyngier <marc.zyngier@arm.com>
> > > ---
> > >  arch/arm/mm/proc-v7-bugs.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++
> > >  arch/arm/mm/proc-v7.S      | 21 +++++++++++++++++++
> > >  2 files changed, 71 insertions(+)
> > > 
> > > diff --git a/arch/arm/mm/proc-v7-bugs.c b/arch/arm/mm/proc-v7-bugs.c
> > > index 65a9b8141f86..0c37e6a2830d 100644
> > > --- a/arch/arm/mm/proc-v7-bugs.c
> > > +++ b/arch/arm/mm/proc-v7-bugs.c
> > > @@ -1,9 +1,12 @@
> > >  // SPDX-License-Identifier: GPL-2.0
> > > +#include <linux/arm-smccc.h>
> > >  #include <linux/kernel.h>
> > > +#include <linux/psci.h>
> > >  #include <linux/smp.h>
> > >  
> > >  #include <asm/cp15.h>
> > >  #include <asm/cputype.h>
> > > +#include <asm/proc-fns.h>
> > >  #include <asm/system_misc.h>
> > >  
> > >  void cpu_v7_bugs_init(void);
> > > @@ -39,6 +42,9 @@ void cpu_v7_ca15_ibe(void)
> > >  #ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
> > >  void (*harden_branch_predictor)(void);
> > >  
> > > +extern void cpu_v7_smc_switch_mm(phys_addr_t pgd_phys, struct mm_struct *mm);
> > > +extern void cpu_v7_hvc_switch_mm(phys_addr_t pgd_phys, struct mm_struct *mm);
> > > +
> > >  static void harden_branch_predictor_bpiall(void)
> > >  {
> > >  	write_sysreg(0, BPIALL);
> > > @@ -49,6 +55,18 @@ static void harden_branch_predictor_iciallu(void)
> > >  	write_sysreg(0, ICIALLU);
> > >  }
> > >  
> > > +#ifdef CONFIG_ARM_PSCI
> > > +static void call_smc_arch_workaround_1(void)
> > > +{
> > > +	arm_smccc_1_1_smc(ARM_SMCCC_ARCH_WORKAROUND_1, NULL);
> > > +}
> > > +
> > > +static void call_hvc_arch_workaround_1(void)
> > > +{
> > > +	arm_smccc_1_1_hvc(ARM_SMCCC_ARCH_WORKAROUND_1, NULL);
> > > +}
> > > +#endif
> > > +
> > >  void cpu_v7_bugs_init(void)
> > >  {
> > >  	const char *spectre_v2_method = NULL;
> > > @@ -73,6 +91,38 @@ void cpu_v7_bugs_init(void)
> > >  		spectre_v2_method = "ICIALLU";
> > >  		break;
> > >  	}
> > > +
> > > +#ifdef CONFIG_ARM_PSCI
> > > +	if (psci_ops.smccc_version != SMCCC_VERSION_1_0) {
> > > +		struct arm_smccc_res res;
> > > +
> > > +		switch (psci_ops.conduit) {
> > > +		case PSCI_CONDUIT_HVC:
> > > +			arm_smccc_1_1_hvc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
> > > +					  ARM_SMCCC_ARCH_WORKAROUND_1, &res);
> > > +			if ((int)res.a0 < 0)
> > > +				break;
> > 
> > I just realised that there is a small, but significant difference
> > between this and the arm64 version: On arm64, we have a table of
> > vulnerable implementations, and we try the mitigation on a per-cpu
> > basis. Here, you entirely rely on the firmware to discover whether the
> > CPU needs mitigation or not. You then need to check for a return value
> > of 1, which indicates that although the mitigation is implemented, it is
> > not required on this particular CPU.
> > 
> > But that's probably moot if you don't support BL systems.
> > 
> > > +			harden_branch_predictor = call_hvc_arch_workaround_1;
> > > +			processor.switch_mm = cpu_v7_hvc_switch_mm;
> > > +			spectre_v2_method = "hypervisor";
> > > +			break;
> > > +
> > > +		case PSCI_CONDUIT_SMC:
> > > +			arm_smccc_1_1_smc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
> > > +					  ARM_SMCCC_ARCH_WORKAROUND_1, &res);
> > > +			if ((int)res.a0 < 0)
> > > +				break;
> > > +			harden_branch_predictor = call_smc_arch_workaround_1;
> > > +			processor.switch_mm = cpu_v7_smc_switch_mm;
> > > +			spectre_v2_method = "firmware PSCI";
> > 
> > My previous remark still stands: this is not really PSCI.
> 
> Sorry, no.  Your comment was for the HVC call, not the SMC.  You said
> nothing about this one.

My bad then. For all intents and purposes, they are the same thing,
just serviced by a different exception level.

	M.

-- 
Jazz is not dead, it just smell funny.