Commit fa9681ed authored by Jiakai Xu's avatar Jiakai Xu Committed by Anup Patel
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RISC-V: KVM: Validate SBI STA shmem alignment in kvm_sbi_ext_sta_set_reg() 



The RISC-V SBI Steal-Time Accounting (STA) extension requires the shared
memory physical address to be 64-byte aligned, or set to all-ones to
explicitly disable steal-time accounting.

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 computed shared memory GPA at the
KVM_SET_ONE_REG boundary. A temporary GPA is constructed and checked
before committing it to vcpu->arch.sta.shmem. The validation allows
either a 64-byte aligned GPA or INVALID_GPA (all-ones), which disables
STA as defined by the SBI specification.

This prevents invalid userspace state from reaching runtime code paths
that assume SBI STA invariants and avoids unexpected WARN_ON behavior.

Fixes: f61ce890 ("RISC-V: KVM: Add support for SBI STA registers")
Signed-off-by: default avatarJiakai Xu <xujiakai2025@iscas.ac.cn>
Signed-off-by: default avatarJiakai Xu <jiakaiPeanut@gmail.com>
Reviewed-by: default avatarAndrew Jones <andrew.jones@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20260303010859.1763177-2-xujiakai2025@iscas.ac.cn


Signed-off-by: default avatarAnup Patel <anup@brainfault.org>
parent c3692998

arch/riscv/kvm/vcpu_sbi_sta.c

+11 −5
Original line number Diff line number Diff line
@@ -181,6 +181,7 @@ static int kvm_sbi_ext_sta_set_reg(struct kvm_vcpu *vcpu, unsigned long reg_num, 
				   unsigned long reg_size, const void *reg_val)

{

	unsigned long value;

	gpa_t new_shmem = INVALID_GPA;



	if (reg_size != sizeof(unsigned long))

		return -EINVAL;
@@ -191,18 +192,18 @@ static int kvm_sbi_ext_sta_set_reg(struct kvm_vcpu *vcpu, unsigned long reg_num, 
		if (IS_ENABLED(CONFIG_32BIT)) {

			gpa_t hi = upper_32_bits(vcpu->arch.sta.shmem);



			vcpu->arch.sta.shmem = value;

			vcpu->arch.sta.shmem |= hi << 32;

			new_shmem = value;

			new_shmem |= hi << 32;

		} else {

			vcpu->arch.sta.shmem = value;

			new_shmem = value;

		}

		break;

	case KVM_REG_RISCV_SBI_STA_REG(shmem_hi):

		if (IS_ENABLED(CONFIG_32BIT)) {

			gpa_t lo = lower_32_bits(vcpu->arch.sta.shmem);



			vcpu->arch.sta.shmem = ((gpa_t)value << 32);

			vcpu->arch.sta.shmem |= lo;

			new_shmem = ((gpa_t)value << 32);

			new_shmem |= lo;

		} else if (value != 0) {

			return -EINVAL;

		}
@@ -211,6 +212,11 @@ static int kvm_sbi_ext_sta_set_reg(struct kvm_vcpu *vcpu, unsigned long reg_num, 
		return -ENOENT;

	}



	if (new_shmem != INVALID_GPA && !IS_ALIGNED(new_shmem, 64))

		return -EINVAL;



	vcpu->arch.sta.shmem = new_shmem;



	return 0;

}