On 8/14/2024 8:52 AM, Isaku Yamahata wrote:
On Wed, Aug 14, 2024 at 11:11:29AM +1200,
"Huang, Kai" <kai.huang@xxxxxxxxx> wrote:
On 14/08/2024 5:50 am, Isaku Yamahata wrote:
On Tue, Aug 13, 2024 at 01:12:55PM +0800,
Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx> wrote:
Check whether a KVM hypercall needs to exit to userspace or not based on
hypercall_exit_enabled field of struct kvm_arch.
Userspace can request a hypercall to exit to userspace for handling by
enable KVM_CAP_EXIT_HYPERCALL and the enabled hypercall will be set in
hypercall_exit_enabled. Make the check code generic based on it.
Signed-off-by: Binbin Wu <binbin.wu@xxxxxxxxxxxxxxx>
---
arch/x86/kvm/x86.c | 4 ++--
arch/x86/kvm/x86.h | 7 +++++++
2 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index af6c8cf6a37a..6e16c9751af7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10226,8 +10226,8 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
cpl = kvm_x86_call(get_cpl)(vcpu);
ret = __kvm_emulate_hypercall(vcpu, nr, a0, a1, a2, a3, op_64_bit, cpl);
- if (nr == KVM_HC_MAP_GPA_RANGE && !ret)
- /* MAP_GPA tosses the request to the user space. */
+ if (!ret && is_kvm_hc_exit_enabled(vcpu->kvm, nr))
+ /* The hypercall is requested to exit to userspace. */
return 0;
if (!op_64_bit)
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 50596f6f8320..0cbec76b42e6 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -547,4 +547,11 @@ int kvm_sev_es_string_io(struct kvm_vcpu *vcpu, unsigned int size,
unsigned int port, void *data, unsigned int count,
int in);
+static inline bool is_kvm_hc_exit_enabled(struct kvm *kvm, unsigned long hc_nr)
+{
+ if(WARN_ON_ONCE(hc_nr >= sizeof(kvm->arch.hypercall_exit_enabled) * 8))
+ return false;
Is this to detect potential bug? Maybe
BUILD_BUG_ON(__builtin_constant_p(hc_nr) &&
!(BIT(hc_nr) & KVM_EXIT_HYPERCALL_VALID_MASK));
Overkill?
My intention was to catch issue when KVM_HC_* grows and exceeds 32.
I was looking a compile time check, but didn't find a proper one.
I don't think this is the correct way to use __builtin_constant_p(), i.e. it
doesn't make sense to use __builtin_constant_p() in BUILD_BUG_ON().
IIUC you need some build time guarantee here, but __builtin_constant_p() can
return false, in which case the above BUILD_BUG_ON() does nothing, which
defeats the purpose.
It depends on what we'd like to detect. BUILT_BUG_ON(__builtin_constant_p())
can detect the usage in the patch 2/2,
is_kvm_hc_exit_enabled(vcpu->kvm, KVM_HC_MAP_GPA_RANGE). The potential
future use of is_kvm_hc_exit_enabled(, KVM_HC_MAP_future_hypercall).
Although this version doesn't help for the one in kvm_emulate_hypercall(),
!ret check is done first to avoid WARN_ON_ONCE() to hit here.
Even !ret is checked first, it's still possible to hit the warning
if KVM_HC_furture_hypercall >=32.
Maybe we can just drop this WARN_ON_ONCE().
Agree that a warning may not be a good option.
What I wanted to guarantee was that "KVM_HC_* < 32" when
hypercall_exit_enabled is u32.
