2021-02-08 21:25:54

by Sean Christopherson

Subject: [PATCH] KVM: x86/xen: Use hva_t for holding hypercall page address

Use hva_t, a.k.a. unsigned long, for the local variable that holds the
hypercall page address. On 32-bit KVM, gcc complains about using a u64
due to the implicit cast from a 64-bit value to a 32-bit pointer.

arch/x86/kvm/xen.c: In function ‘kvm_xen_write_hypercall_page’:
arch/x86/kvm/xen.c:300:22: error: cast to pointer from integer of
different size [-Werror=int-to-pointer-cast]
300 | page = memdup_user((u8 __user *)blob_addr, PAGE_SIZE);

Cc: Joao Martins <[email protected]>
Cc: David Woodhouse <[email protected]>
Fixes: 23200b7a30de ("KVM: x86/xen: intercept xen hypercalls if enabled")
Signed-off-by: Sean Christopherson <[email protected]>
---
arch/x86/kvm/xen.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 2cee0376455c..deda1ba8c18a 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -286,8 +286,12 @@ int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
return 1;
}
} else {
- u64 blob_addr = lm ? kvm->arch.xen_hvm_config.blob_addr_64
- : kvm->arch.xen_hvm_config.blob_addr_32;
+ /*
+ * Note, truncation is a non-issue as 'lm' is guaranteed to be
+ * false for a 32-bit kernel, i.e. when hva_t is only 4 bytes.
+ */
+ hva_t blob_addr = lm ? kvm->arch.xen_hvm_config.blob_addr_64
+ : kvm->arch.xen_hvm_config.blob_addr_32;
u8 blob_size = lm ? kvm->arch.xen_hvm_config.blob_size_64
: kvm->arch.xen_hvm_config.blob_size_32;
u8 *page;
--
2.30.0.478.g8a0d178c01-goog

2021-02-08 21:27:50

by Woodhouse, David

Subject: Re: [PATCH] KVM: x86/xen: Use hva_t for holding hypercall page address

On Mon, 2021-02-08 at 12:15 -0800, Sean Christopherson wrote:
> Use hva_t, a.k.a. unsigned long, for the local variable that holds the
> hypercall page address. On 32-bit KVM, gcc complains about using a u64
> due to the implicit cast from a 64-bit value to a 32-bit pointer.
>
> arch/x86/kvm/xen.c: In function ‘kvm_xen_write_hypercall_page’:
> arch/x86/kvm/xen.c:300:22: error: cast to pointer from integer of
> different size [-Werror=int-to-pointer-cast]
> 300 | page = memdup_user((u8 __user *)blob_addr, PAGE_SIZE);

Thanks.

Acked-by: David Woodhouse <[email protected]>

> Cc: Joao Martins <[email protected]>
> Cc: David Woodhouse <[email protected]>
> Fixes: 23200b7a30de ("KVM: x86/xen: intercept xen hypercalls if enabled")
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
> arch/x86/kvm/xen.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
> index 2cee0376455c..deda1ba8c18a 100644
> --- a/arch/x86/kvm/xen.c
> +++ b/arch/x86/kvm/xen.c
> @@ -286,8 +286,12 @@ int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
> return 1;
> }
> } else {
> - u64 blob_addr = lm ? kvm->arch.xen_hvm_config.blob_addr_64
> - : kvm->arch.xen_hvm_config.blob_addr_32;
> + /*
> + * Note, truncation is a non-issue as 'lm' is guaranteed to be
> + * false for a 32-bit kernel, i.e. when hva_t is only 4 bytes.
> + */
> + hva_t blob_addr = lm ? kvm->arch.xen_hvm_config.blob_addr_64
> + : kvm->arch.xen_hvm_config.blob_addr_32;
> u8 blob_size = lm ? kvm->arch.xen_hvm_config.blob_size_64
> : kvm->arch.xen_hvm_config.blob_size_32;
> u8 *page;
> --
> 2.30.0.478.g8a0d178c01-goog
>




Amazon Development Centre (London) Ltd. Registered in England and Wales with registration number 04543232 with its registered office at 1 Principal Place, Worship Street, London EC2A 2FA, United Kingdom.

2021-02-08 21:32:40

by Joao Martins

Subject: Re: [PATCH] KVM: x86/xen: Use hva_t for holding hypercall page address

On 2/8/21 8:15 PM, Sean Christopherson wrote:
> Use hva_t, a.k.a. unsigned long, for the local variable that holds the
> hypercall page address. On 32-bit KVM, gcc complains about using a u64
> due to the implicit cast from a 64-bit value to a 32-bit pointer.
>
> arch/x86/kvm/xen.c: In function ‘kvm_xen_write_hypercall_page’:
> arch/x86/kvm/xen.c:300:22: error: cast to pointer from integer of
> different size [-Werror=int-to-pointer-cast]
> 300 | page = memdup_user((u8 __user *)blob_addr, PAGE_SIZE);
>
> Cc: Joao Martins <[email protected]>
> Cc: David Woodhouse <[email protected]>
> Fixes: 23200b7a30de ("KVM: x86/xen: intercept xen hypercalls if enabled")
> Signed-off-by: Sean Christopherson <[email protected]>

Reviewed-by: Joao Martins <[email protected]>

> ---
> arch/x86/kvm/xen.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
> index 2cee0376455c..deda1ba8c18a 100644
> --- a/arch/x86/kvm/xen.c
> +++ b/arch/x86/kvm/xen.c
> @@ -286,8 +286,12 @@ int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
> return 1;
> }
> } else {
> - u64 blob_addr = lm ? kvm->arch.xen_hvm_config.blob_addr_64
> - : kvm->arch.xen_hvm_config.blob_addr_32;
> + /*
> + * Note, truncation is a non-issue as 'lm' is guaranteed to be
> + * false for a 32-bit kernel, i.e. when hva_t is only 4 bytes.
> + */
> + hva_t blob_addr = lm ? kvm->arch.xen_hvm_config.blob_addr_64
> + : kvm->arch.xen_hvm_config.blob_addr_32;
> u8 blob_size = lm ? kvm->arch.xen_hvm_config.blob_size_64
> : kvm->arch.xen_hvm_config.blob_size_32;
> u8 *page;
>

2021-02-09 09:30:55

by Paolo Bonzini

Subject: Re: [PATCH] KVM: x86/xen: Use hva_t for holding hypercall page address

On 08/02/21 21:15, Sean Christopherson wrote:
> Use hva_t, a.k.a. unsigned long, for the local variable that holds the
> hypercall page address. On 32-bit KVM, gcc complains about using a u64
> due to the implicit cast from a 64-bit value to a 32-bit pointer.
>
> arch/x86/kvm/xen.c: In function ‘kvm_xen_write_hypercall_page’:
> arch/x86/kvm/xen.c:300:22: error: cast to pointer from integer of
> different size [-Werror=int-to-pointer-cast]
> 300 | page = memdup_user((u8 __user *)blob_addr, PAGE_SIZE);
>
> Cc: Joao Martins <[email protected]>
> Cc: David Woodhouse <[email protected]>
> Fixes: 23200b7a30de ("KVM: x86/xen: intercept xen hypercalls if enabled")
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
> arch/x86/kvm/xen.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
> index 2cee0376455c..deda1ba8c18a 100644
> --- a/arch/x86/kvm/xen.c
> +++ b/arch/x86/kvm/xen.c
> @@ -286,8 +286,12 @@ int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
> return 1;
> }
> } else {
> - u64 blob_addr = lm ? kvm->arch.xen_hvm_config.blob_addr_64
> - : kvm->arch.xen_hvm_config.blob_addr_32;
> + /*
> + * Note, truncation is a non-issue as 'lm' is guaranteed to be
> + * false for a 32-bit kernel, i.e. when hva_t is only 4 bytes.
> + */
> + hva_t blob_addr = lm ? kvm->arch.xen_hvm_config.blob_addr_64
> + : kvm->arch.xen_hvm_config.blob_addr_32;
> u8 blob_size = lm ? kvm->arch.xen_hvm_config.blob_size_64
> : kvm->arch.xen_hvm_config.blob_size_32;
> u8 *page;
>

Queued, thanks.

Paolo