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Commit 7fafcbb0 authored by Will Deacon's avatar Will Deacon Committed by Greg Kroah-Hartman
Browse files

arm64: entry: Add fake CPU feature for unmapping the kernel at EL0 




Commit ea1e3de85e94 upstream.

Allow explicit disabling of the entry trampoline on the kernel command
line (kpti=off) by adding a fake CPU feature (ARM64_UNMAP_KERNEL_AT_EL0)
that can be used to toggle the alternative sequences in our entry code and
avoid use of the trampoline altogether if desired. This also allows us to
make use of a static key in arm64_kernel_unmapped_at_el0().

Reviewed-by: default avatarMark Rutland <mark.rutland@arm.com>
Tested-by: default avatarLaura Abbott <labbott@redhat.com>
Tested-by: default avatarShanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 2843ade2

arch/arm64/include/asm/cpucaps.h

+2 −1
Original line number Diff line number Diff line
@@ -40,7 +40,8 @@ 
#define ARM64_WORKAROUND_858921			19

#define ARM64_WORKAROUND_CAVIUM_30115		20

#define ARM64_HAS_DCPOP				21

#define ARM64_UNMAP_KERNEL_AT_EL0		23



#define ARM64_NCAPS				22

#define ARM64_NCAPS				24



#endif /* __ASM_CPUCAPS_H */

arch/arm64/include/asm/mmu.h

+2 −1
Original line number Diff line number Diff line
@@ -36,7 +36,8 @@ typedef struct { 


static inline bool arm64_kernel_unmapped_at_el0(void)

{

	return IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0);

	return IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0) &&

	       cpus_have_const_cap(ARM64_UNMAP_KERNEL_AT_EL0);

}



extern void paging_init(void);

arch/arm64/kernel/cpufeature.c

+41 −0
Original line number Diff line number Diff line
@@ -796,6 +796,40 @@ static bool has_no_fpsimd(const struct arm64_cpu_capabilities *entry, int __unus 
					ID_AA64PFR0_FP_SHIFT) < 0;

}



#ifdef CONFIG_UNMAP_KERNEL_AT_EL0

static int __kpti_forced; /* 0: not forced, >0: forced on, <0: forced off */



static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,

				int __unused)

{

	/* Forced on command line? */

	if (__kpti_forced) {

		pr_info_once("kernel page table isolation forced %s by command line option\n",

			     __kpti_forced > 0 ? "ON" : "OFF");

		return __kpti_forced > 0;

	}



	/* Useful for KASLR robustness */

	if (IS_ENABLED(CONFIG_RANDOMIZE_BASE))

		return true;



	return false;

}



static int __init parse_kpti(char *str)

{

	bool enabled;

	int ret = strtobool(str, &enabled);



	if (ret)

		return ret;



	__kpti_forced = enabled ? 1 : -1;

	return 0;

}

__setup("kpti=", parse_kpti);

#endif	/* CONFIG_UNMAP_KERNEL_AT_EL0 */



static const struct arm64_cpu_capabilities arm64_features[] = {

	{

		.desc = "GIC system register CPU interface",
@@ -882,6 +916,13 @@ static const struct arm64_cpu_capabilities arm64_features[] = { 
		.def_scope = SCOPE_SYSTEM,

		.matches = hyp_offset_low,

	},

#ifdef CONFIG_UNMAP_KERNEL_AT_EL0

	{

		.capability = ARM64_UNMAP_KERNEL_AT_EL0,

		.def_scope = SCOPE_SYSTEM,

		.matches = unmap_kernel_at_el0,

	},

#endif

	{

		/* FP/SIMD is not implemented */

		.capability = ARM64_HAS_NO_FPSIMD,

arch/arm64/kernel/entry.S

+5 −4
Original line number Diff line number Diff line
@@ -74,6 +74,7 @@ 
	.macro kernel_ventry, el, label, regsize = 64

	.align 7

#ifdef CONFIG_UNMAP_KERNEL_AT_EL0

alternative_if ARM64_UNMAP_KERNEL_AT_EL0

	.if	\el == 0

	.if	\regsize == 64

	mrs	x30, tpidrro_el0
@@ -82,6 +83,7 @@ 
	mov	x30, xzr

	.endif

	.endif

alternative_else_nop_endif

#endif



	sub	sp, sp, #S_FRAME_SIZE
@@ -321,10 +323,9 @@ alternative_else_nop_endif 
	ldr	lr, [sp, #S_LR]

	add	sp, sp, #S_FRAME_SIZE		// restore sp



#ifndef CONFIG_UNMAP_KERNEL_AT_EL0

	eret

#else

	.if	\el == 0

alternative_insn eret, nop, ARM64_UNMAP_KERNEL_AT_EL0

#ifdef CONFIG_UNMAP_KERNEL_AT_EL0

	bne	4f

	msr	far_el1, x30

	tramp_alias	x30, tramp_exit_native
@@ -332,10 +333,10 @@ alternative_else_nop_endif 
4:

	tramp_alias	x30, tramp_exit_compat

	br	x30

#endif

	.else

	eret

	.endif

#endif

	.endm



	.macro	irq_stack_entry