Commit 16dbe77a authored by Yeoreum Yun's avatar Yeoreum Yun Committed by Catalin Marinas
Browse files

KVM: arm64: Use CAST instruction for swapping guest descriptor 



Use the CAST instruction to swap the guest descriptor when FEAT_LSUI
is enabled, avoiding the need to clear the PAN bit.

FEAT_LSUI is introduced in Armv9.6, where FEAT_PAN is mandatory. However,
this assumption may not always hold:

 - Some CPUs may advertise FEAT_LSUI but lack FEAT_PAN.
 - Virtualization or ID register overrides may expose invalid feature
   combinations.

Therefore, instead of disabling FEAT_LSUI when FEAT_PAN is absent, wrap
LSUI instructions with uaccess_ttbr0_enable()/disable() when
ARM64_SW_TTBR0_PAN is enabled.

Signed-off-by: default avatarYeoreum Yun <yeoreum.yun@arm.com>
Reviewed-by: default avatarMarc Zyngier <maz@kernel.org>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 44adf2bf

arch/arm64/kvm/at.c

+33 −1
Original line number Diff line number Diff line
@@ -9,6 +9,7 @@ 
#include <asm/esr.h>

#include <asm/kvm_hyp.h>

#include <asm/kvm_mmu.h>

#include <asm/lsui.h>



static void fail_s1_walk(struct s1_walk_result *wr, u8 fst, bool s1ptw)

{
@@ -1681,6 +1682,35 @@ int __kvm_find_s1_desc_level(struct kvm_vcpu *vcpu, u64 va, u64 ipa, int *level) 
	}

}



static int __lsui_swap_desc(u64 __user *ptep, u64 old, u64 new)

{

	u64 tmp = old;

	int ret = 0;



	/*

	 * Wrap LSUI instructions with uaccess_ttbr0_enable()/disable(),

	 * as PAN toggling is not required.

	 */

	uaccess_ttbr0_enable();



	asm volatile(__LSUI_PREAMBLE

		     "1: cast	%[old], %[new], %[addr]\n"

		     "2:\n"

		     _ASM_EXTABLE_UACCESS_ERR(1b, 2b, %w[ret])

		     : [old] "+r" (old), [addr] "+Q" (*ptep), [ret] "+r" (ret)

		     : [new] "r" (new)

		     : "memory");



	uaccess_ttbr0_disable();



	if (ret)

		return ret;

	if (tmp != old)

		return -EAGAIN;



	return ret;

}



static int __lse_swap_desc(u64 __user *ptep, u64 old, u64 new)

{

	u64 tmp = old;
@@ -1756,7 +1786,9 @@ int __kvm_at_swap_desc(struct kvm *kvm, gpa_t ipa, u64 old, u64 new) 
		return -EPERM;



	ptep = (u64 __user *)hva + offset;

	if (cpus_have_final_cap(ARM64_HAS_LSE_ATOMICS))

	if (cpus_have_final_cap(ARM64_HAS_LSUI))

		r = __lsui_swap_desc(ptep, old, new);

	else if (cpus_have_final_cap(ARM64_HAS_LSE_ATOMICS))

		r = __lse_swap_desc(ptep, old, new);

	else

		r = __llsc_swap_desc(ptep, old, new);