kvm_riscv_vcpu_record_steal_time() assumes that the steal-time shared
memory GPA (vcpu->arch.sta.shmem) is always backed by a valid guest
memory slot. However, this assumption is not guaranteed by the KVM
userspace ABI.

A malicious or buggy userspace can set the STA shared memory GPA via
KVM_SET_ONE_REG without establishing a corresponding memory region via
KVM_SET_USER_MEMORY_REGION. In such cases, the GPA cannot be translated
to a valid HVA and kvm_vcpu_gfn_to_hva() returns an error address.

The current implementation incorrectly treats this as a kernel warning
using WARN_ON(), which may escalate to a kernel panic when panic_on_warn
is enabled.

This is not a kernel bug condition but a normal invalid configuration
from userspace, and should be handled gracefully.

Fix it by removing WARN_ON() and treating invalid HVA as a normal
failure case, resetting the STA shared memory state.

Fixes: e9f12b5fff8ad0 ("RISC-V: KVM: Implement SBI STA extension")
Signed-off-by: Jiakai Xu <xujiakai2025@iscas.ac.cn>
Signed-off-by: Jiakai Xu <jiakaiPeanut@gmail.com>
Assisted-by: OpenClaw:DeepSeek-V3.2
---
 arch/riscv/kvm/vcpu_sbi_sta.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/riscv/kvm/vcpu_sbi_sta.c b/arch/riscv/kvm/vcpu_sbi_sta.c
index 3b834709b429f..60e50296a0085 100644
--- a/arch/riscv/kvm/vcpu_sbi_sta.c
+++ b/arch/riscv/kvm/vcpu_sbi_sta.c
@@ -46,7 +46,7 @@ void kvm_riscv_vcpu_record_steal_time(struct kvm_vcpu *vcpu)
 	gfn = shmem >> PAGE_SHIFT;
 	hva = kvm_vcpu_gfn_to_hva(vcpu, gfn);
 
-	if (WARN_ON(kvm_is_error_hva(hva))) {
+	if (kvm_is_error_hva(hva)) {
 		vcpu->arch.sta.shmem = INVALID_GPA;
 		return;
 	}
-- 
2.34.1

On Wed, Apr 15, 2026 at 1:22 PM Jiakai Xu <xujiakai2025@iscas.ac.cn> wrote:
>
> kvm_riscv_vcpu_record_steal_time() assumes that the steal-time shared
> memory GPA (vcpu->arch.sta.shmem) is always backed by a valid guest
> memory slot. However, this assumption is not guaranteed by the KVM
> userspace ABI.
>
> A malicious or buggy userspace can set the STA shared memory GPA via
> KVM_SET_ONE_REG without establishing a corresponding memory region via
> KVM_SET_USER_MEMORY_REGION. In such cases, the GPA cannot be translated
> to a valid HVA and kvm_vcpu_gfn_to_hva() returns an error address.
>
> The current implementation incorrectly treats this as a kernel warning
> using WARN_ON(), which may escalate to a kernel panic when panic_on_warn
> is enabled.
>
> This is not a kernel bug condition but a normal invalid configuration
> from userspace, and should be handled gracefully.
>
> Fix it by removing WARN_ON() and treating invalid HVA as a normal
> failure case, resetting the STA shared memory state.
>
> Fixes: e9f12b5fff8ad0 ("RISC-V: KVM: Implement SBI STA extension")
> Signed-off-by: Jiakai Xu <xujiakai2025@iscas.ac.cn>
> Signed-off-by: Jiakai Xu <jiakaiPeanut@gmail.com>
> Assisted-by: OpenClaw:DeepSeek-V3.2

Queued this as fix for Linux-7.1-rcX

Thanks,
Anup

> ---
>  arch/riscv/kvm/vcpu_sbi_sta.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kvm/vcpu_sbi_sta.c b/arch/riscv/kvm/vcpu_sbi_sta.c
> index 3b834709b429f..60e50296a0085 100644
> --- a/arch/riscv/kvm/vcpu_sbi_sta.c
> +++ b/arch/riscv/kvm/vcpu_sbi_sta.c
> @@ -46,7 +46,7 @@ void kvm_riscv_vcpu_record_steal_time(struct kvm_vcpu *vcpu)
>         gfn = shmem >> PAGE_SHIFT;
>         hva = kvm_vcpu_gfn_to_hva(vcpu, gfn);
>
> -       if (WARN_ON(kvm_is_error_hva(hva))) {
> +       if (kvm_is_error_hva(hva)) {
>                 vcpu->arch.sta.shmem = INVALID_GPA;
>                 return;
>         }
> --
> 2.34.1
>

On Wed, Apr 15, 2026 at 07:52:16AM +0000, Jiakai Xu wrote:
> kvm_riscv_vcpu_record_steal_time() assumes that the steal-time shared
> memory GPA (vcpu->arch.sta.shmem) is always backed by a valid guest
> memory slot. However, this assumption is not guaranteed by the KVM
> userspace ABI.
> 
> A malicious or buggy userspace can set the STA shared memory GPA via
> KVM_SET_ONE_REG without establishing a corresponding memory region via
> KVM_SET_USER_MEMORY_REGION. In such cases, the GPA cannot be translated
> to a valid HVA and kvm_vcpu_gfn_to_hva() returns an error address.
> 
> The current implementation incorrectly treats this as a kernel warning
> using WARN_ON(), which may escalate to a kernel panic when panic_on_warn
> is enabled.
> 
> This is not a kernel bug condition but a normal invalid configuration
> from userspace, and should be handled gracefully.
> 
> Fix it by removing WARN_ON() and treating invalid HVA as a normal
> failure case, resetting the STA shared memory state.
> 
> Fixes: e9f12b5fff8ad0 ("RISC-V: KVM: Implement SBI STA extension")
> Signed-off-by: Jiakai Xu <xujiakai2025@iscas.ac.cn>
> Signed-off-by: Jiakai Xu <jiakaiPeanut@gmail.com>
> Assisted-by: OpenClaw:DeepSeek-V3.2
> ---
>  arch/riscv/kvm/vcpu_sbi_sta.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/kvm/vcpu_sbi_sta.c b/arch/riscv/kvm/vcpu_sbi_sta.c
> index 3b834709b429f..60e50296a0085 100644
> --- a/arch/riscv/kvm/vcpu_sbi_sta.c
> +++ b/arch/riscv/kvm/vcpu_sbi_sta.c
> @@ -46,7 +46,7 @@ void kvm_riscv_vcpu_record_steal_time(struct kvm_vcpu *vcpu)
>  	gfn = shmem >> PAGE_SHIFT;
>  	hva = kvm_vcpu_gfn_to_hva(vcpu, gfn);
>  
> -	if (WARN_ON(kvm_is_error_hva(hva))) {
> +	if (kvm_is_error_hva(hva)) {
>  		vcpu->arch.sta.shmem = INVALID_GPA;
>  		return;
>  	}
> -- 
> 2.34.1
>

Reviewed-by: Andrew Jones <andrew.jones@oss.qualcomm.com>