* [PATCH] KVM: x86: Add more protection against undefined behavior in rsvd_bits()
@ 2021-01-13 20:45 Sean Christopherson
2021-01-18 17:34 ` Paolo Bonzini
0 siblings, 1 reply; 2+ messages in thread
From: Sean Christopherson @ 2021-01-13 20:45 UTC (permalink / raw)
To: Paolo Bonzini
Cc: Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
Joerg Roedel, kvm, linux-kernel
Add compile-time asserts in rsvd_bits() to guard against KVM passing in
garbage hardcoded values, and cap the upper bound at '63' for dynamic
values to prevent generating a mask that would overflow a u64.
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/mmu.h | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 581925e476d6..261be1d2032b 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -44,8 +44,15 @@
#define PT32_ROOT_LEVEL 2
#define PT32E_ROOT_LEVEL 3
-static inline u64 rsvd_bits(int s, int e)
+static __always_inline u64 rsvd_bits(int s, int e)
{
+ BUILD_BUG_ON(__builtin_constant_p(e) && __builtin_constant_p(s) && e < s);
+
+ if (__builtin_constant_p(e))
+ BUILD_BUG_ON(e > 63);
+ else
+ e &= 63;
+
if (e < s)
return 0;
--
2.30.0.284.gd98b1dd5eaa7-goog
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] KVM: x86: Add more protection against undefined behavior in rsvd_bits()
2021-01-13 20:45 [PATCH] KVM: x86: Add more protection against undefined behavior in rsvd_bits() Sean Christopherson
@ 2021-01-18 17:34 ` Paolo Bonzini
0 siblings, 0 replies; 2+ messages in thread
From: Paolo Bonzini @ 2021-01-18 17:34 UTC (permalink / raw)
To: Sean Christopherson
Cc: Vitaly Kuznetsov, Wanpeng Li, Jim Mattson, Joerg Roedel, kvm,
linux-kernel
On 13/01/21 21:45, Sean Christopherson wrote:
> Add compile-time asserts in rsvd_bits() to guard against KVM passing in
> garbage hardcoded values, and cap the upper bound at '63' for dynamic
> values to prevent generating a mask that would overflow a u64.
>
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/mmu.h | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index 581925e476d6..261be1d2032b 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -44,8 +44,15 @@
> #define PT32_ROOT_LEVEL 2
> #define PT32E_ROOT_LEVEL 3
>
> -static inline u64 rsvd_bits(int s, int e)
> +static __always_inline u64 rsvd_bits(int s, int e)
> {
> + BUILD_BUG_ON(__builtin_constant_p(e) && __builtin_constant_p(s) && e < s);
> +
> + if (__builtin_constant_p(e))
> + BUILD_BUG_ON(e > 63);
> + else
> + e &= 63;
> +
> if (e < s)
> return 0;
>
>
Queued for 5.11, thanks.
Paolo
^ permalink raw reply [flat|nested] 2+ messages in thread
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