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Commit f763322f authored by Will Deacon's avatar Will Deacon Committed by Gerrit - the friendly Code Review server
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arm64: Add skeleton to harden the branch predictor against aliasing attacks 



Aliasing attacks against CPU branch predictors can allow an attacker to
redirect speculative control flow on some CPUs and potentially divulge
information from one context to another.

This patch adds initial skeleton code behind a new Kconfig option to
enable implementation-specific mitigations against these attacks for
CPUs that are affected.

Change-Id: I778641a6a2658cded427204a8c2b01dc6b6b9579
Co-developed-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
Git-commit: 0f15adbb2861ce6f75ccfc5a92b19eae0ef327d0
Git-repo: https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux


[neeraju@codeaurora.org: Fix merge conflicts and build failures
 due to missing includes and api changes in new kernels]
Signed-off-by: default avatarNeeraj Upadhyay <neeraju@codeaurora.org>
parent 92725fdc

arch/arm64/Kconfig

+17 −0
Original line number Diff line number Diff line
@@ -813,6 +813,23 @@ config UNMAP_KERNEL_AT_EL0 


	  If unsure, say Y.



config HARDEN_BRANCH_PREDICTOR

	bool "Harden the branch predictor against aliasing attacks" if EXPERT

	default y

	help

	  Speculation attacks against some high-performance processors rely on

	  being able to manipulate the branch predictor for a victim context by

	  executing aliasing branches in the attacker context.  Such attacks

	  can be partially mitigated against by clearing internal branch

	  predictor state and limiting the prediction logic in some situations.



	  This config option will take CPU-specific actions to harden the

	  branch predictor against aliasing attacks and may rely on specific

	  instruction sequences or control bits being set by the system

	  firmware.



	  If unsure, say Y.



menuconfig ARMV8_DEPRECATED

	bool "Emulate deprecated/obsolete ARMv8 instructions"

	depends on COMPAT

arch/arm64/include/asm/cpufeature.h

+1 −0
Original line number Diff line number Diff line
@@ -29,6 +29,7 @@ 
#define ARM64_HAS_PAN				4

#define ARM64_HAS_UAO				5

#define ARM64_ALT_PAN_NOT_UAO			6

#define ARM64_HARDEN_BRANCH_PREDICTOR		7

#define ARM64_UNMAP_KERNEL_AT_EL0		23



#define ARM64_NCAPS				24

arch/arm64/include/asm/mmu.h

+40 −0
Original line number Diff line number Diff line
@@ -21,7 +21,10 @@ 


#ifndef __ASSEMBLY__



#include <linux/smp.h>



#include <asm/cpufeature.h>

#include <asm/percpu.h>



typedef struct {

	atomic64_t	id;
@@ -41,6 +44,43 @@ static inline bool arm64_kernel_unmapped_at_el0(void) 
	       cpus_have_cap(ARM64_UNMAP_KERNEL_AT_EL0);

}



typedef void (*bp_hardening_cb_t)(void);



struct bp_hardening_data {

	int			hyp_vectors_slot;

	bp_hardening_cb_t	fn;

};



#ifdef CONFIG_HARDEN_BRANCH_PREDICTOR

extern char __bp_harden_hyp_vecs_start[], __bp_harden_hyp_vecs_end[];



DECLARE_PER_CPU_READ_MOSTLY(struct bp_hardening_data, bp_hardening_data);



static inline struct bp_hardening_data *arm64_get_bp_hardening_data(void)

{

	return this_cpu_ptr(&bp_hardening_data);

}



static inline void arm64_apply_bp_hardening(void)

{

	struct bp_hardening_data *d;



	if (!cpus_have_cap(ARM64_HARDEN_BRANCH_PREDICTOR))

		return;



	d = arm64_get_bp_hardening_data();

	if (d->fn)

		d->fn();

}

#else

static inline struct bp_hardening_data *arm64_get_bp_hardening_data(void)

{

	return NULL;

}



static inline void arm64_apply_bp_hardening(void)	{ }

#endif	/* CONFIG_HARDEN_BRANCH_PREDICTOR */



extern void paging_init(void);

extern void __iomem *early_io_map(phys_addr_t phys, unsigned long virt);

extern void init_mem_pgprot(void);

arch/arm64/include/asm/sysreg.h

+1 −0
Original line number Diff line number Diff line
@@ -101,6 +101,7 @@ 
#define ID_AA64ISAR0_AES_SHIFT		4



/* id_aa64pfr0 */

#define ID_AA64PFR0_CSV2_SHIFT		56

#define ID_AA64PFR0_GIC_SHIFT		24

#define ID_AA64PFR0_ASIMD_SHIFT		20

#define ID_AA64PFR0_FP_SHIFT		16

arch/arm64/kernel/Makefile

+4 −0
Original line number Diff line number Diff line
@@ -42,6 +42,10 @@ arm64-obj-$(CONFIG_ARMV8_DEPRECATED) += armv8_deprecated.o 
arm64-obj-$(CONFIG_MSM_APP_API)		+= app_api.o

arm64-obj-$(CONFIG_MSM_APP_SETTINGS)	+= app_setting.o



ifeq ($(CONFIG_KVM),y)

arm64-obj-$(CONFIG_HARDEN_BRANCH_PREDICTOR)	+= bpi.o

endif



obj-y					+= $(arm64-obj-y) vdso/

obj-m					+= $(arm64-obj-m)

head-y					:= head.o