Commit 3b2e00f1 authored Nov 30, 2023 by Heiko Carstens Committed by Alexander Gordeev Dec 11, 2023

KVM: s390: use READ_ONCE() to read fpc register value

Use READ_ONCE() to read a vcpu's floating point register value from
the memory mapped area. This avoids that, depending on code
generation, a different value is tested for validity than the one that
is used, since user space can modify the area concurrently and the
compiler is free to generate code that reads the value multiple times.

Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

parent b988b1bb

arch/s390/kvm/kvm-s390.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -4962,7 +4962,7 @@ static void sync_regs(struct kvm_vcpu *vcpu)
		current->thread.fpu.regs = vcpu->run->s.regs.vrs;
		else
		current->thread.fpu.regs = vcpu->run->s.regs.fprs;
		current->thread.fpu.fpc = vcpu->run->s.regs.fpc;
		current->thread.fpu.fpc = READ_ONCE(vcpu->run->s.regs.fpc);
		if (test_fp_ctl(current->thread.fpu.fpc))
		/* User space provided an invalid FPC, let's clear it */
		current->thread.fpu.fpc = 0;