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([210.73.43.101]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-35335215eb5sm10523533a91.5.2026.01.25.20.28.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 25 Jan 2026 20:28:32 -0800 (PST) From: Jiakai Xu X-Google-Original-From: Jiakai Xu To: linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, kvm-riscv@lists.infradead.org, kvm@vger.kernel.org Cc: Alexandre Ghiti , Albert Ou , Palmer Dabbelt , Paul Walmsley , Atish Patra , Anup Patel , Jiakai Xu , Jiakai Xu Subject: [PATCH v3] RISC-V: KVM: Validate SBI STA shmem alignment in kvm_sbi_ext_sta_set_reg() Date: Mon, 26 Jan 2026 04:28:25 +0000 Message-Id: <20260126042825.2810142-1-xujiakai2025@iscas.ac.cn> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The RISC-V SBI Steal-Time Accounting (STA) extension requires the shared memory physical address to be 64-byte aligned, and the shared memory size to be at least 64 bytes. KVM exposes the SBI STA shared memory configuration to userspace via KVM_SET_ONE_REG. However, the current implementation of kvm_sbi_ext_sta_set_reg() does not validate the alignment of the configured shared memory address. As a result, userspace can install a misaligned shared memory address that violates the SBI specification. Such an invalid configuration may later reach runtime code paths that assume a valid and properly aligned shared memory region. In particular, KVM_RUN can trigger the following WARN_ON in kvm_riscv_vcpu_record_steal_time(): WARNING: arch/riscv/kvm/vcpu_sbi_sta.c:49 at kvm_riscv_vcpu_record_steal_time WARN_ON paths are not expected to be reachable during normal runtime execution, and may result in a kernel panic when panic_on_warn is enabled. Fix this by validating the shared memory alignment at the KVM_SET_ONE_REG boundary and rejecting misaligned configurations with -EINVAL. The validation is performed on a temporary computed address and only committed to vcpu->arch.sta.shmem once it is known to be valid,=20 similar to the existing logic in kvm_sbi_sta_steal_time_set_shmem() and kvm_sbi_ext_sta_handler(). With this change, invalid userspace state is rejected early and cannot reach runtime code paths that rely on the SBI specification invariants. A reproducer triggering the WARN_ON and the complete kernel log are available at: https://github.com/j1akai/temp/tree/main/20260124 Fixes: f61ce890b1f074 ("RISC-V: KVM: Add support for SBI STA registers") Signed-off-by: Jiakai Xu Signed-off-by: Jiakai Xu --- V2 -> V3: Added parentheses to function name in subject. V1 -> V2: Added Fixes tag. arch/riscv/kvm/vcpu_sbi_sta.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/arch/riscv/kvm/vcpu_sbi_sta.c b/arch/riscv/kvm/vcpu_sbi_sta.c index afa0545c3bcfc..7dfe671c42eaa 100644 --- a/arch/riscv/kvm/vcpu_sbi_sta.c +++ b/arch/riscv/kvm/vcpu_sbi_sta.c @@ -186,23 +186,25 @@ static int kvm_sbi_ext_sta_set_reg(struct kvm_vcpu *v= cpu, unsigned long reg_num, return -EINVAL; value =3D *(const unsigned long *)reg_val; =20 + gpa_t new_shmem =3D vcpu->arch.sta.shmem; + switch (reg_num) { case KVM_REG_RISCV_SBI_STA_REG(shmem_lo): if (IS_ENABLED(CONFIG_32BIT)) { gpa_t hi =3D upper_32_bits(vcpu->arch.sta.shmem); =20 - vcpu->arch.sta.shmem =3D value; - vcpu->arch.sta.shmem |=3D hi << 32; + new_shmem =3D value; + new_shmem |=3D hi << 32; } else { - vcpu->arch.sta.shmem =3D value; + new_shmem =3D value; } break; case KVM_REG_RISCV_SBI_STA_REG(shmem_hi): if (IS_ENABLED(CONFIG_32BIT)) { gpa_t lo =3D lower_32_bits(vcpu->arch.sta.shmem); =20 - vcpu->arch.sta.shmem =3D ((gpa_t)value << 32); - vcpu->arch.sta.shmem |=3D lo; + new_shmem =3D ((gpa_t)value << 32); + new_shmem |=3D lo; } else if (value !=3D 0) { return -EINVAL; } @@ -210,7 +212,10 @@ static int kvm_sbi_ext_sta_set_reg(struct kvm_vcpu *vc= pu, unsigned long reg_num, default: return -ENOENT; } + if (new_shmem && !IS_ALIGNED(new_shmem, 64)) + return -EINVAL; =20 + vcpu->arch.sta.shmem =3D new_shmem; return 0; } =20 --=20 2.34.1