linux-kernel - [PATCH] RISC-V: KVM: fix stack overrun when loading vlenb

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Message-ID: <20250805104418.196023-4-rkrcmar@ventanamicro.com>
Date: Tue,  5 Aug 2025 12:44:21 +0200
From: Radim Krčmář <rkrcmar@...tanamicro.com>
To: kvm-riscv@...ts.infradead.org
Cc: kvm@...r.kernel.org,
	linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Anup Patel <anup@...infault.org>,
	Atish Patra <atishp@...shpatra.org>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Alexandre Ghiti <alex@...ti.fr>,
	Daniel Henrique Barboza <dbarboza@...tanamicro.com>,
	stable@...r.kernel.org
Subject: [PATCH] RISC-V: KVM: fix stack overrun when loading vlenb

The userspace load can put up to 2048 bits into an xlen bit stack
buffer.  We want only xlen bits, so check the size beforehand.

Fixes: 2fa290372dfe ("RISC-V: KVM: add 'vlenb' Vector CSR")
Cc: <stable@...r.kernel.org>
Signed-off-by: Radim Krčmář <rkrcmar@...tanamicro.com>
---
 arch/riscv/kvm/vcpu_vector.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/riscv/kvm/vcpu_vector.c b/arch/riscv/kvm/vcpu_vector.c
index a5f88cb717f3..05f3cc2d8e31 100644
--- a/arch/riscv/kvm/vcpu_vector.c
+++ b/arch/riscv/kvm/vcpu_vector.c
@@ -182,6 +182,8 @@ int kvm_riscv_vcpu_set_reg_vector(struct kvm_vcpu *vcpu,
 		struct kvm_cpu_context *cntx = &vcpu->arch.guest_context;
 		unsigned long reg_val;
 
+		if (reg_size != sizeof(reg_val))
+			return -EINVAL;
 		if (copy_from_user(&reg_val, uaddr, reg_size))
 			return -EFAULT;
 		if (reg_val != cntx->vector.vlenb)
-- 
2.50.0