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

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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 b68f3cc7d9, "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: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson
2019-09-27 14:45:20 -07:00
committed by Paolo Bonzini
parent 491c1ad1ac
commit 489cbcf01d
2 changed files with 10 additions and 8 deletions
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6
arch/x86/kvm/x86.h
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@@ -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;