Commit 93ad55b7 authored by Marc Zyngier's avatar Marc Zyngier Committed by Will Deacon
Browse files

arm64: cpufeatures: Allow disabling of BTI from the command-line 



In order to be able to disable BTI at runtime, whether it is
for testing purposes, or to work around HW issues, let's add
support for overriding the ID_AA64PFR1_EL1.BTI field.

This is further mapped on the arm64.nobti command-line alias.

Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Acked-by: default avatarDavid Brazdil <dbrazdil@google.com>
Tested-by: default avatarSrinivas Ramana <sramana@codeaurora.org>
Link: https://lore.kernel.org/r/20210208095732.3267263-21-maz@kernel.org


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent a762f4ff

Documentation/admin-guide/kernel-parameters.txt

+3 −0
Original line number Diff line number Diff line
@@ -373,6 +373,9 @@ 
	arcrimi=	[HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards

			Format: <io>,<irq>,<nodeID>



	arm64.nobti	[ARM64] Unconditionally disable Branch Target

			Identification support



	ataflop=	[HW,M68k]



	atarimouse=	[HW,MOUSE] Atari Mouse

arch/arm64/include/asm/cpufeature.h

+1 −0
Original line number Diff line number Diff line
@@ -819,6 +819,7 @@ static inline unsigned int get_vmid_bits(u64 mmfr1) 
}



extern struct arm64_ftr_override id_aa64mmfr1_override;

extern struct arm64_ftr_override id_aa64pfr1_override;



u32 get_kvm_ipa_limit(void);

void dump_cpu_features(void);

arch/arm64/kernel/cpufeature.c

+3 −1
Original line number Diff line number Diff line
@@ -558,6 +558,7 @@ static const struct arm64_ftr_bits ftr_raz[] = { 
#define ARM64_FTR_REG(id, table) ARM64_FTR_REG_OVERRIDE(id, table, &no_override)



struct arm64_ftr_override __ro_after_init id_aa64mmfr1_override;

struct arm64_ftr_override __ro_after_init id_aa64pfr1_override;



static const struct __ftr_reg_entry {

	u32			sys_id;
@@ -593,7 +594,8 @@ static const struct __ftr_reg_entry { 


	/* Op1 = 0, CRn = 0, CRm = 4 */

	ARM64_FTR_REG(SYS_ID_AA64PFR0_EL1, ftr_id_aa64pfr0),

	ARM64_FTR_REG(SYS_ID_AA64PFR1_EL1, ftr_id_aa64pfr1),

	ARM64_FTR_REG_OVERRIDE(SYS_ID_AA64PFR1_EL1, ftr_id_aa64pfr1,

			       &id_aa64pfr1_override),

	ARM64_FTR_REG(SYS_ID_AA64ZFR0_EL1, ftr_id_aa64zfr0),



	/* Op1 = 0, CRn = 0, CRm = 5 */

arch/arm64/kernel/idreg-override.c

+11 −0
Original line number Diff line number Diff line
@@ -37,6 +37,15 @@ static const struct ftr_set_desc mmfr1 __initconst = { 
	},

};



static const struct ftr_set_desc pfr1 __initconst = {

	.name		= "id_aa64pfr1",

	.override	= &id_aa64pfr1_override,

	.fields		= {

	        { "bt", ID_AA64PFR1_BT_SHIFT },

		{}

	},

};



extern struct arm64_ftr_override kaslr_feature_override;



static const struct ftr_set_desc kaslr __initconst = {
@@ -52,6 +61,7 @@ static const struct ftr_set_desc kaslr __initconst = { 


static const struct ftr_set_desc * const regs[] __initconst = {

	&mmfr1,

	&pfr1,

	&kaslr,

};
@@ -61,6 +71,7 @@ static const struct { 
} aliases[] __initconst = {

	{ "kvm-arm.mode=nvhe",		"id_aa64mmfr1.vh=0" },

	{ "kvm-arm.mode=protected",	"id_aa64mmfr1.vh=0" },

	{ "arm64.nobti",		"id_aa64pfr1.bt=0" },

	{ "nokaslr",			"kaslr.disabled=1" },

};

arch/arm64/mm/mmu.c

+1 −1
Original line number Diff line number Diff line
@@ -628,7 +628,7 @@ static bool arm64_early_this_cpu_has_bti(void) 
	if (!IS_ENABLED(CONFIG_ARM64_BTI_KERNEL))

		return false;



	pfr1 = read_sysreg_s(SYS_ID_AA64PFR1_EL1);

	pfr1 = __read_sysreg_by_encoding(SYS_ID_AA64PFR1_EL1);

	return cpuid_feature_extract_unsigned_field(pfr1,

						    ID_AA64PFR1_BT_SHIFT);

}