Commit 4ad3a0b8 authored by Oliver Upton's avatar Oliver Upton Committed by Marc Zyngier
Browse files

KVM: arm64: Don't hijack guest context MDSCR_EL1 



Stealing MDSCR_EL1 in the guest's kvm_cpu_context for external debugging
is rather gross. Just add a field for this instead and let the context
switch code pick the correct one based on the debug owner.

Tested-by: default avatarJames Clark <james.clark@linaro.org>
Signed-off-by: default avatarOliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20241219224116.3941496-15-oliver.upton@linux.dev


Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
parent 75a5fbaf

arch/arm64/include/asm/kvm_host.h

+1 −1
Original line number Diff line number Diff line
@@ -751,6 +751,7 @@ struct kvm_vcpu_arch { 
	 */

	struct kvm_guest_debug_arch vcpu_debug_state;

	struct kvm_guest_debug_arch external_debug_state;

	u64 external_mdscr_el1;



	enum {

		VCPU_DEBUG_FREE,
@@ -771,7 +772,6 @@ struct kvm_vcpu_arch { 
	 * are using guest debug.

	 */

	struct {

		u32	mdscr_el1;

		bool	pstate_ss;

	} guest_debug_preserved;

arch/arm64/kvm/debug.c

+36 −39
Original line number Diff line number Diff line
@@ -31,19 +31,12 @@ 
 */

static void save_guest_debug_regs(struct kvm_vcpu *vcpu)

{

	u64 val = vcpu_read_sys_reg(vcpu, MDSCR_EL1);



	vcpu->arch.guest_debug_preserved.mdscr_el1 = val;

	vcpu->arch.guest_debug_preserved.pstate_ss =

					(*vcpu_cpsr(vcpu) & DBG_SPSR_SS);

}



static void restore_guest_debug_regs(struct kvm_vcpu *vcpu)

{

	u64 val = vcpu->arch.guest_debug_preserved.mdscr_el1;



	vcpu_write_sys_reg(vcpu, val, MDSCR_EL1);



	if (vcpu->arch.guest_debug_preserved.pstate_ss)

		*vcpu_cpsr(vcpu) |= DBG_SPSR_SS;

	else
@@ -115,8 +108,6 @@ static void kvm_arm_setup_mdcr_el2(struct kvm_vcpu *vcpu) 


void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)

{

	unsigned long mdscr;



	/* Check if we need to use the debug registers. */

	if (vcpu->guest_debug || kvm_vcpu_os_lock_enabled(vcpu)) {

		/* Save guest debug state */
@@ -154,36 +145,6 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) 
				*vcpu_cpsr(vcpu) |= DBG_SPSR_SS;

			else

				*vcpu_cpsr(vcpu) &= ~DBG_SPSR_SS;



			mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);

			mdscr |= DBG_MDSCR_SS;

			vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);

		} else {

			mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);

			mdscr &= ~DBG_MDSCR_SS;

			vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);

		}



		/*

		 * Enable breakpoints and watchpoints if userspace wants them.

		 */

		if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {

			mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);

			mdscr |= DBG_MDSCR_MDE;

			vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);



		/*

		 * The OS Lock blocks debug exceptions in all ELs when it is

		 * enabled. If the guest has enabled the OS Lock, constrain its

		 * effects to the guest. Emulate the behavior by clearing

		 * MDSCR_EL1.MDE. In so doing, we ensure that host debug

		 * exceptions are unaffected by guest configuration of the OS

		 * Lock.

		 */

		} else if (kvm_vcpu_os_lock_enabled(vcpu)) {

			mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);

			mdscr &= ~DBG_MDSCR_MDE;

			vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);

		}

	}

}
@@ -227,6 +188,41 @@ void kvm_init_host_debug_data(void) 
		host_data_set_flag(HAS_TRBE);

}



/*

 * Configures the 'external' MDSCR_EL1 value for the guest, i.e. when the host

 * has taken over MDSCR_EL1.

 *

 *  - Userspace is single-stepping the guest, and MDSCR_EL1.SS is forced to 1.

 *

 *  - Userspace is using the breakpoint/watchpoint registers to debug the

 *    guest, and MDSCR_EL1.MDE is forced to 1.

 *

 *  - The guest has enabled the OS Lock, and KVM is forcing MDSCR_EL1.MDE to 0,

 *    masking all debug exceptions affected by the OS Lock.

 */

static void setup_external_mdscr(struct kvm_vcpu *vcpu)

{

	/*

	 * Use the guest's MDSCR_EL1 as a starting point, since there are

	 * several other features controlled by MDSCR_EL1 that are not relevant

	 * to the host.

	 *

	 * Clear the bits that KVM may use which also satisfies emulation of

	 * the OS Lock as MDSCR_EL1.MDE is cleared.

	 */

	u64 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1) & ~(MDSCR_EL1_SS |

							   MDSCR_EL1_MDE |

							   MDSCR_EL1_KDE);



	if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)

		mdscr |= MDSCR_EL1_SS;



	if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW)

		mdscr |= MDSCR_EL1_MDE | MDSCR_EL1_KDE;



	vcpu->arch.external_mdscr_el1 = mdscr;

}



void kvm_vcpu_load_debug(struct kvm_vcpu *vcpu)

{

	u64 mdscr;
@@ -249,6 +245,7 @@ void kvm_vcpu_load_debug(struct kvm_vcpu *vcpu) 
	 */

	if (vcpu->guest_debug || kvm_vcpu_os_lock_enabled(vcpu)) {

		vcpu->arch.debug_owner = VCPU_DEBUG_HOST_OWNED;

		setup_external_mdscr(vcpu);

	} else {

		mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);

arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h

+27 −12
Original line number Diff line number Diff line
@@ -18,9 +18,34 @@ 


static inline bool ctxt_has_s1poe(struct kvm_cpu_context *ctxt);



static inline struct kvm_vcpu *ctxt_to_vcpu(struct kvm_cpu_context *ctxt)

{

	struct kvm_vcpu *vcpu = ctxt->__hyp_running_vcpu;



	if (!vcpu)

		vcpu = container_of(ctxt, struct kvm_vcpu, arch.ctxt);



	return vcpu;

}



static inline bool ctxt_is_guest(struct kvm_cpu_context *ctxt)

{

	return host_data_ptr(host_ctxt) != ctxt;

}



static inline u64 *ctxt_mdscr_el1(struct kvm_cpu_context *ctxt)

{

	struct kvm_vcpu *vcpu = ctxt_to_vcpu(ctxt);



	if (ctxt_is_guest(ctxt) && kvm_host_owns_debug_regs(vcpu))

		return &vcpu->arch.external_mdscr_el1;



	return &ctxt_sys_reg(ctxt, MDSCR_EL1);

}



static inline void __sysreg_save_common_state(struct kvm_cpu_context *ctxt)

{

	ctxt_sys_reg(ctxt, MDSCR_EL1)	= read_sysreg(mdscr_el1);

	*ctxt_mdscr_el1(ctxt)	= read_sysreg(mdscr_el1);



	// POR_EL0 can affect uaccess, so must be saved/restored early.

	if (ctxt_has_s1poe(ctxt))
@@ -33,16 +58,6 @@ static inline void __sysreg_save_user_state(struct kvm_cpu_context *ctxt) 
	ctxt_sys_reg(ctxt, TPIDRRO_EL0)	= read_sysreg(tpidrro_el0);

}



static inline struct kvm_vcpu *ctxt_to_vcpu(struct kvm_cpu_context *ctxt)

{

	struct kvm_vcpu *vcpu = ctxt->__hyp_running_vcpu;



	if (!vcpu)

		vcpu = container_of(ctxt, struct kvm_vcpu, arch.ctxt);



	return vcpu;

}



static inline bool ctxt_has_mte(struct kvm_cpu_context *ctxt)

{

	struct kvm_vcpu *vcpu = ctxt_to_vcpu(ctxt);
@@ -139,7 +154,7 @@ static inline void __sysreg_save_el2_return_state(struct kvm_cpu_context *ctxt) 


static inline void __sysreg_restore_common_state(struct kvm_cpu_context *ctxt)

{

	write_sysreg(ctxt_sys_reg(ctxt, MDSCR_EL1),  mdscr_el1);

	write_sysreg(*ctxt_mdscr_el1(ctxt),  mdscr_el1);



	// POR_EL0 can affect uaccess, so must be saved/restored early.

	if (ctxt_has_s1poe(ctxt))