Commit 489cbcf0 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: x86: Add WARNs to detect out-of-bounds register indices 



Add WARN_ON_ONCE() checks in kvm_register_{read,write}() to detect reg
values that would cause KVM to overflow vcpu->arch.regs.  Change the reg
param to an 'int' to make it clear that the reg index is unverified.

Regarding the overhead of WARN_ON_ONCE(), now that all fixed GPR reads
and writes use dedicated accessors, e.g. kvm_rax_read(), the overhead
is limited to flows where the reg index is generated at runtime.  And
there is at least one historical bug where KVM has generated an out-of-
bounds access to arch.regs (see commit b68f3cc7, "KVM: x86: Always
use 32-bit SMRAM save state for 32-bit kernels").

Adding the WARN_ON_ONCE() protection paves the way for additional
cleanup related to kvm_reg and kvm_reg_ex.

Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 491c1ad1

arch/x86/kvm/kvm_cache_regs.h

+8 −4
Original line number Diff line number Diff line
@@ -37,19 +37,23 @@ BUILD_KVM_GPR_ACCESSORS(r14, R14) 
BUILD_KVM_GPR_ACCESSORS(r15, R15)

#endif



static inline unsigned long kvm_register_read(struct kvm_vcpu *vcpu,

					      enum kvm_reg reg)

static inline unsigned long kvm_register_read(struct kvm_vcpu *vcpu, int reg)

{

	if (WARN_ON_ONCE((unsigned int)reg >= NR_VCPU_REGS))

		return 0;



	if (!test_bit(reg, (unsigned long *)&vcpu->arch.regs_avail))

		kvm_x86_ops->cache_reg(vcpu, reg);



	return vcpu->arch.regs[reg];

}



static inline void kvm_register_write(struct kvm_vcpu *vcpu,

				      enum kvm_reg reg,

static inline void kvm_register_write(struct kvm_vcpu *vcpu, int reg,

				      unsigned long val)

{

	if (WARN_ON_ONCE((unsigned int)reg >= NR_VCPU_REGS))

		return;



	vcpu->arch.regs[reg] = val;

	__set_bit(reg, (unsigned long *)&vcpu->arch.regs_dirty);

	__set_bit(reg, (unsigned long *)&vcpu->arch.regs_avail);

arch/x86/kvm/x86.h

+2 −4
Original line number Diff line number Diff line
@@ -238,8 +238,7 @@ static inline bool vcpu_match_mmio_gpa(struct kvm_vcpu *vcpu, gpa_t gpa) 
	return false;

}



static inline unsigned long kvm_register_readl(struct kvm_vcpu *vcpu,

					       enum kvm_reg reg)

static inline unsigned long kvm_register_readl(struct kvm_vcpu *vcpu, int reg)

{

	unsigned long val = kvm_register_read(vcpu, reg);
@@ -247,8 +246,7 @@ static inline unsigned long kvm_register_readl(struct kvm_vcpu *vcpu, 
}



static inline void kvm_register_writel(struct kvm_vcpu *vcpu,

				       enum kvm_reg reg,

				       unsigned long val)

				       int reg, unsigned long val)

{

	if (!is_64_bit_mode(vcpu))

		val = (u32)val;

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