Commit 7db21530 authored by Andrew Scull's avatar Andrew Scull Committed by Marc Zyngier
Browse files

KVM: arm64: Restore hyp when panicking in guest context 



If the guest context is loaded when a panic is triggered, restore the
hyp context so e.g. the shadow call stack works when hyp_panic() is
called and SP_EL0 is valid when the host's panic() is called.

Use the hyp context's __hyp_running_vcpu field to track when hyp
transitions to and from the guest vcpu so the exception handlers know
whether the context needs to be restored.

Signed-off-by: default avatarAndrew Scull <ascull@google.com>
Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200915104643.2543892-11-ascull@google.com
parent 7c2e76d8

arch/arm64/include/asm/kvm_asm.h

+10 −0
Original line number Diff line number Diff line
@@ -236,6 +236,16 @@ extern char __smccc_workaround_1_smc[__SMCCC_WORKAROUND_1_SMC_SZ]; 
	ldr	\vcpu, [\ctxt, #HOST_CONTEXT_VCPU]

.endm



.macro get_loaded_vcpu vcpu, ctxt

	hyp_adr_this_cpu \ctxt, kvm_hyp_ctxt, \vcpu

	ldr	\vcpu, [\ctxt, #HOST_CONTEXT_VCPU]

.endm



.macro set_loaded_vcpu vcpu, ctxt, tmp

	hyp_adr_this_cpu \ctxt, kvm_hyp_ctxt, \tmp

	str	\vcpu, [\ctxt, #HOST_CONTEXT_VCPU]

.endm



/*

 * KVM extable for unexpected exceptions.

 * In the same format _asm_extable, but output to a different section so that

arch/arm64/kvm/hyp/entry.S

+24 −0
Original line number Diff line number Diff line
@@ -86,6 +86,8 @@ alternative_else_nop_endif 
	ret



1:

	set_loaded_vcpu x0, x1, x2



	add	x29, x0, #VCPU_CONTEXT



	// Macro ptrauth_switch_to_guest format:
@@ -116,6 +118,26 @@ alternative_else_nop_endif 
	eret

	sb



SYM_INNER_LABEL(__guest_exit_panic, SYM_L_GLOBAL)

	// x2-x29,lr: vcpu regs

	// vcpu x0-x1 on the stack



	// If the hyp context is loaded, go straight to hyp_panic

	get_loaded_vcpu x0, x1

	cbz	x0, hyp_panic



	// The hyp context is saved so make sure it is restored to allow

	// hyp_panic to run at hyp and, subsequently, panic to run in the host.

	// This makes use of __guest_exit to avoid duplication but sets the

	// return address to tail call into hyp_panic. As a side effect, the

	// current state is saved to the guest context but it will only be

	// accurate if the guest had been completely restored.

	hyp_adr_this_cpu x0, kvm_hyp_ctxt, x1

	adr	x1, hyp_panic

	str	x1, [x0, #CPU_XREG_OFFSET(30)]



	get_vcpu_ptr	x1, x0



SYM_INNER_LABEL(__guest_exit, SYM_L_GLOBAL)

	// x0: return code

	// x1: vcpu
@@ -163,6 +185,8 @@ SYM_INNER_LABEL(__guest_exit, SYM_L_GLOBAL) 
	// Now restore the hyp regs

	restore_callee_saved_regs x2



	set_loaded_vcpu xzr, x1, x2



alternative_if ARM64_HAS_RAS_EXTN

	// If we have the RAS extensions we can consume a pending error

	// without an unmask-SError and isb. The ESB-instruction consumed any

arch/arm64/kvm/hyp/hyp-entry.S

+2 −3
Original line number Diff line number Diff line
@@ -145,7 +145,7 @@ el2_error: 
	eret

	sb



.macro invalid_vector	label, target = hyp_panic

.macro invalid_vector	label, target = __guest_exit_panic

	.align	2

SYM_CODE_START(\label)

	b \target
@@ -186,10 +186,9 @@ check_preamble_length 661b, 662b 
.macro invalid_vect target

	.align 7

661:

	b	\target

	nop

	stp	x0, x1, [sp, #-16]!

662:

	ldp	x0, x1, [sp], #16

	b	\target



check_preamble_length 661b, 662b

arch/arm64/kvm/hyp/include/hyp/switch.h

+3 −1
Original line number Diff line number Diff line
@@ -509,6 +509,7 @@ static inline void __set_host_arch_workaround_state(struct kvm_vcpu *vcpu) 


static inline void __kvm_unexpected_el2_exception(void)

{

	extern char __guest_exit_panic[];

	unsigned long addr, fixup;

	struct exception_table_entry *entry, *end;

	unsigned long elr_el2 = read_sysreg(elr_el2);
@@ -529,7 +530,8 @@ static inline void __kvm_unexpected_el2_exception(void) 
		return;

	}



	hyp_panic();

	/* Trigger a panic after restoring the hyp context. */

	write_sysreg(__guest_exit_panic, elr_el2);

}



#endif /* __ARM64_KVM_HYP_SWITCH_H__ */

arch/arm64/kvm/hyp/nvhe/host.S

+5 −0
Original line number Diff line number Diff line
@@ -75,6 +75,11 @@ SYM_FUNC_END(__hyp_do_panic) 


.macro invalid_host_vect

	.align 7

	/* If a guest is loaded, panic out of it. */

	stp	x0, x1, [sp, #-16]!

	get_loaded_vcpu x0, x1

	cbnz	x0, __guest_exit_panic

	add	sp, sp, #16

	b	hyp_panic

.endm

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