From 428b8f1d9f92f838b73997adc10046d3c6e05790 Mon Sep 17 00:00:00 2001 From: Nick Desaulniers Date: Mon, 23 Mar 2020 12:12:43 -0700 Subject: KVM: VMX: don't allow memory operands for inline asm that modifies SP THUNK_TARGET defines [thunk_target] as having "rm" input constraints when CONFIG_RETPOLINE is not set, which isn't constrained enough for this specific case. For inline assembly that modifies the stack pointer before using this input, the underspecification of constraints is dangerous, and results in an indirect call to a previously pushed flags register. In this case `entry`'s stack slot is good enough to satisfy the "m" constraint in "rm", but the inline assembly in handle_external_interrupt_irqoff() modifies the stack pointer via push+pushf before using this input, which in this case results in calling what was the previous state of the flags register, rather than `entry`. Be more specific in the constraints by requiring `entry` be in a register, and not a memory operand. Reported-by: Dmitry Vyukov Reported-by: syzbot+3f29ca2efb056a761e38@syzkaller.appspotmail.com Debugged-by: Alexander Potapenko Debugged-by: Paolo Bonzini Debugged-by: Sean Christopherson Signed-off-by: Nick Desaulniers Message-Id: <20200323191243.30002-1-ndesaulniers@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/vmx/vmx.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch') diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 26f8f31563e9..079d9fbf278e 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6287,7 +6287,7 @@ static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu) #endif ASM_CALL_CONSTRAINT : - THUNK_TARGET(entry), + [thunk_target]"r"(entry), [ss]"i"(__KERNEL_DS), [cs]"i"(__KERNEL_CS) ); -- cgit v1.2.3-58-ga151