2023-01-12 16:48:16

by Isaku Yamahata

Subject: [PATCH v11 032/113] KVM: x86/mmu: Add Suppress VE bit to shadow_mmio_mask

From: Isaku Yamahata <[email protected]>

To make use of the same value of shadow_mmio_mask for TDX and VMX, add
Suppress-VE bit to shadow_mmio_mask so that shadow_mmio_mask can be common
for both VMX and TDX.

TDX will need shadow_mmio_mask to be VMX_SUPPRESS_VE | RWX and
shadow_mmio_value to be 0 so that EPT violation is triggered. For VMX,
VMX_SUPPRESS_VE doesn't matter because the spte value is required to cause
EPT misconfig. the additional bit doesn't affect VMX logic to add the bit
to shadow_mmio_{value, mask}.

Signed-off-by: Isaku Yamahata <[email protected]>
---
arch/x86/kvm/mmu/spte.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
index fce6f047399f..cc0bc058fb25 100644
--- a/arch/x86/kvm/mmu/spte.c
+++ b/arch/x86/kvm/mmu/spte.c
@@ -431,7 +431,9 @@ void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only)
shadow_dirty_mask = has_ad_bits ? VMX_EPT_DIRTY_BIT : 0ull;
shadow_nx_mask = 0ull;
shadow_x_mask = VMX_EPT_EXECUTABLE_MASK;
- shadow_present_mask = has_exec_only ? 0ull : VMX_EPT_READABLE_MASK;
+ /* VMX_EPT_SUPPRESS_VE_BIT is needed for W or X violation. */
+ shadow_present_mask =
+ (has_exec_only ? 0ull : VMX_EPT_READABLE_MASK) | VMX_EPT_SUPPRESS_VE_BIT;
/*
* EPT overrides the host MTRRs, and so KVM must program the desired
* memtype directly into the SPTEs. Note, this mask is just the mask
@@ -448,7 +450,7 @@ void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only)
* of an EPT paging-structure entry is 110b (write/execute).
*/
kvm_mmu_set_mmio_spte_mask(VMX_EPT_MISCONFIG_WX_VALUE,
- VMX_EPT_RWX_MASK, 0);
+ VMX_EPT_RWX_MASK | VMX_EPT_SUPPRESS_VE_BIT, 0);
}
EXPORT_SYMBOL_GPL(kvm_mmu_set_ept_masks);

--
2.25.1

2023-01-16 11:14:20

by Kai Huang

Subject: Re: [PATCH v11 032/113] KVM: x86/mmu: Add Suppress VE bit to shadow_mmio_mask

On Thu, 2023-01-12 at 08:31 -0800, [email protected] wrote:
> From: Isaku Yamahata <[email protected]>
>
> To make use of the same value of shadow_mmio_mask for TDX and VMX, add
> Suppress-VE bit to shadow_mmio_mask so that shadow_mmio_mask can be common
> for both VMX and TDX.
>
> TDX will need shadow_mmio_mask to be VMX_SUPPRESS_VE | RWX and
> shadow_mmio_value to be 0 so that EPT violation is triggered. For VMX,
> VMX_SUPPRESS_VE doesn't matter because the spte value is required to cause
> EPT misconfig. the additional bit doesn't affect VMX logic to add the bit
> to shadow_mmio_{value, mask}.
>
> Signed-off-by: Isaku Yamahata <[email protected]>
> ---
> arch/x86/kvm/mmu/spte.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
> index fce6f047399f..cc0bc058fb25 100644
> --- a/arch/x86/kvm/mmu/spte.c
> +++ b/arch/x86/kvm/mmu/spte.c
> @@ -431,7 +431,9 @@ void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only)
> shadow_dirty_mask = has_ad_bits ? VMX_EPT_DIRTY_BIT : 0ull;
> shadow_nx_mask = 0ull;
> shadow_x_mask = VMX_EPT_EXECUTABLE_MASK;
> - shadow_present_mask = has_exec_only ? 0ull : VMX_EPT_READABLE_MASK;
> + /* VMX_EPT_SUPPRESS_VE_BIT is needed for W or X violation. */
> + shadow_present_mask =
> + (has_exec_only ? 0ull : VMX_EPT_READABLE_MASK) | VMX_EPT_SUPPRESS_VE_BIT;

This chunk has nothing to do with what this patch claims to do.

> /*
> * EPT overrides the host MTRRs, and so KVM must program the desired
> * memtype directly into the SPTEs. Note, this mask is just the mask
> @@ -448,7 +450,7 @@ void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only)
> * of an EPT paging-structure entry is 110b (write/execute).
> */
> kvm_mmu_set_mmio_spte_mask(VMX_EPT_MISCONFIG_WX_VALUE,
> - VMX_EPT_RWX_MASK, 0);
> + VMX_EPT_RWX_MASK | VMX_EPT_SUPPRESS_VE_BIT, 0);
> }
> EXPORT_SYMBOL_GPL(kvm_mmu_set_ept_masks);
>