From 0d033770d43a7aa36025bcef9a60da7fb750f735 Mon Sep 17 00:00:00 2001 From: Michal Luczaj Date: Fri, 28 Jul 2023 02:12:57 +0200 Subject: [PATCH] KVM: x86: Fix KVM_CAP_SYNC_REGS's sync_regs() TOCTOU issues In a spirit of using a sledgehammer to crack a nut, make sync_regs() feed __set_sregs() and kvm_vcpu_ioctl_x86_set_vcpu_events() with kernel's own copy of data. Both __set_sregs() and kvm_vcpu_ioctl_x86_set_vcpu_events() assume they have exclusive rights to structs they operate on. While this is true when coming from an ioctl handler (caller makes a local copy of user's data), sync_regs() breaks this contract; a pointer to a user-modifiable memory (vcpu->run->s.regs) is provided. This can lead to a situation when incoming data is checked and/or sanitized only to be re-set by a user thread running in parallel. Signed-off-by: Michal Luczaj Fixes: 01643c51bfcf ("KVM: x86: KVM_CAP_SYNC_REGS") Link: https://lore.kernel.org/r/20230728001606.2275586-2-mhal@rbox.co Signed-off-by: Sean Christopherson --- arch/x86/kvm/x86.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index a6b9bea6..0145d84 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11777,15 +11777,22 @@ static int sync_regs(struct kvm_vcpu *vcpu) __set_regs(vcpu, &vcpu->run->s.regs.regs); vcpu->run->kvm_dirty_regs &= ~KVM_SYNC_X86_REGS; } + if (vcpu->run->kvm_dirty_regs & KVM_SYNC_X86_SREGS) { - if (__set_sregs(vcpu, &vcpu->run->s.regs.sregs)) + struct kvm_sregs sregs = vcpu->run->s.regs.sregs; + + if (__set_sregs(vcpu, &sregs)) return -EINVAL; + vcpu->run->kvm_dirty_regs &= ~KVM_SYNC_X86_SREGS; } + if (vcpu->run->kvm_dirty_regs & KVM_SYNC_X86_EVENTS) { - if (kvm_vcpu_ioctl_x86_set_vcpu_events( - vcpu, &vcpu->run->s.regs.events)) + struct kvm_vcpu_events events = vcpu->run->s.regs.events; + + if (kvm_vcpu_ioctl_x86_set_vcpu_events(vcpu, &events)) return -EINVAL; + vcpu->run->kvm_dirty_regs &= ~KVM_SYNC_X86_EVENTS; } -- 2.7.4