Commit d87a8e65 authored by Mark Rutland's avatar Mark Rutland Committed by Catalin Marinas
Browse files

arm64: head.S: always initialize PSTATE 



As with SCTLR_ELx and other control registers, some PSTATE bits are
UNKNOWN out-of-reset, and we may not be able to rely on hardware or
firmware to initialize them to our liking prior to entry to the kernel,
e.g. in the primary/secondary boot paths and return from idle/suspend.

It would be more robust (and easier to reason about) if we consistently
initialized PSTATE to a default value, as we do with control registers.
This will ensure that the kernel is not adversely affected by bits it is
not aware of, e.g. when support for a feature such as PAN/UAO is
disabled.

This patch ensures that PSTATE is consistently initialized at boot time
via an ERET. This is not intended to relax the existing requirements
(e.g. DAIF bits must still be set prior to entering the kernel). For
features detected dynamically (which may require system-wide support),
it is still necessary to subsequently modify PSTATE.

As ERET is not always a Context Synchronization Event, an ISB is placed
before each exception return to ensure updates to control registers have
taken effect. This handles the kernel being entered with SCTLR_ELx.EOS
clear (or any future control bits being in an UNKNOWN state).

Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20201113124937.20574-6-mark.rutland@arm.com


Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 2ffac9e3

arch/arm64/include/asm/ptrace.h

+5 −0
Original line number Diff line number Diff line
@@ -16,6 +16,11 @@ 
#define CurrentEL_EL1		(1 << 2)

#define CurrentEL_EL2		(2 << 2)



#define INIT_PSTATE_EL1 \

	(PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT | PSR_MODE_EL1h)

#define INIT_PSTATE_EL2 \

	(PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT | PSR_MODE_EL2h)



/*

 * PMR values used to mask/unmask interrupts.

 *

arch/arm64/kernel/head.S

+21 −11
Original line number Diff line number Diff line
@@ -486,21 +486,29 @@ EXPORT_SYMBOL(kimage_vaddr) 
 * reachable EL supported by the kernel in a chosen default state. If dropping

 * from EL2 to EL1, configure EL2 before configuring EL1.

 *

 * Since we cannot always rely on ERET synchronizing writes to sysregs (e.g. if

 * SCTLR_ELx.EOS is clear), we place an ISB prior to ERET.

 *

 * Returns either BOOT_CPU_MODE_EL1 or BOOT_CPU_MODE_EL2 in w0 if

 * booted in EL1 or EL2 respectively.

 */

SYM_FUNC_START(init_kernel_el)

	msr	SPsel, #1			// We want to use SP_EL{1,2}

	mrs	x0, CurrentEL

	cmp	x0, #CurrentEL_EL2

	b.eq	1f

	b.eq	init_el2



SYM_INNER_LABEL(init_el1, SYM_L_LOCAL)

	mov_q	x0, INIT_SCTLR_EL1_MMU_OFF

	msr	sctlr_el1, x0

	mov	w0, #BOOT_CPU_MODE_EL1		// This cpu booted in EL1

	isb

	ret

	mov_q	x0, INIT_PSTATE_EL1

	msr	spsr_el1, x0

	msr	elr_el1, lr

	mov	w0, #BOOT_CPU_MODE_EL1

	eret



1:	mov_q	x0, INIT_SCTLR_EL2_MMU_OFF

SYM_INNER_LABEL(init_el2, SYM_L_LOCAL)

	mov_q	x0, INIT_SCTLR_EL2_MMU_OFF

	msr	sctlr_el2, x0



#ifdef CONFIG_ARM64_VHE
@@ -609,9 +617,12 @@ set_hcr: 


	cbz	x2, install_el2_stub



	mov	w0, #BOOT_CPU_MODE_EL2		// This CPU booted in EL2

	isb

	ret

	mov_q	x0, INIT_PSTATE_EL2

	msr	spsr_el2, x0

	msr	elr_el2, lr

	mov	w0, #BOOT_CPU_MODE_EL2

	eret



SYM_INNER_LABEL(install_el2_stub, SYM_L_LOCAL)

	/*
@@ -643,12 +654,11 @@ SYM_INNER_LABEL(install_el2_stub, SYM_L_LOCAL) 
7:	adr_l	x0, __hyp_stub_vectors

	msr	vbar_el2, x0



	/* spsr */

	mov	x0, #(PSR_F_BIT | PSR_I_BIT | PSR_A_BIT | PSR_D_BIT |\

		      PSR_MODE_EL1h)

	isb

	mov	x0, #INIT_PSTATE_EL1

	msr	spsr_el2, x0

	msr	elr_el2, lr

	mov	w0, #BOOT_CPU_MODE_EL2		// This CPU booted in EL2

	mov	w0, #BOOT_CPU_MODE_EL2

	eret

SYM_FUNC_END(init_kernel_el)

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