[PATCH v4 6/9] riscv: ptrace: validate input vector csr registers

From: Sergey Matyukevich <geomatsi@gmail.com>
To: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	linux-kselftest@vger.kernel.org
Cc: Paul Walmsley <pjw@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Alexandre Ghiti <alex@ghiti.fr>, Oleg Nesterov <oleg@redhat.com>,
	Shuah Khan <shuah@kernel.org>, Thomas Huth <thuth@redhat.com>,
	Charlie Jenkins <charlie@rivosinc.com>,
	Andy Chiu <andybnac@gmail.com>,
	Samuel Holland <samuel.holland@sifive.com>,
	Joel Granados <joel.granados@kernel.org>,
	Conor Dooley <conor.dooley@microchip.com>,
	Yong-Xuan Wang <yongxuan.wang@sifive.com>,
	Heiko Stuebner <heiko@sntech.de>,
	Sergey Matyukevich <geomatsi@gmail.com>
Subject: [PATCH v4 6/9] riscv: ptrace: validate input vector csr registers
Date: Sat,  8 Nov 2025 22:41:45 +0300	[thread overview]
Message-ID: <20251108194207.1257866-7-geomatsi@gmail.com> (raw)
In-Reply-To: <20251108194207.1257866-1-geomatsi@gmail.com>

Add strict validation for vector csr registers when setting them via
ptrace:
- reject attempts to set reserved bits or invalid field combinations
- enforce strict VL checks against calculated VLMAX values

Vector spec 1.0 allows normal applications to set candidate VL values
and read back the hardware-adjusted results, see section 6 for details.
Disallow such flexibility in vector ptrace operations and strictly
enforce valid VL input.

The traced process may not update its saved vector context if no vector
instructions execute between breakpoints. So the purpose of the strict
ptrace approach is to make sure that debuggers maintain an accurate view
of the tracee's vector context across multiple halt/resume debug cycles.

Signed-off-by: Sergey Matyukevich <geomatsi@gmail.com>
---
 arch/riscv/kernel/ptrace.c | 62 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 61 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c
index 906cf1197edc..a567e558e746 100644
--- a/arch/riscv/kernel/ptrace.c
+++ b/arch/riscv/kernel/ptrace.c
@@ -124,6 +124,66 @@ static int riscv_vr_get(struct task_struct *target,
 	return membuf_write(&to, vstate->datap, riscv_v_vsize);
 }
 
+static int invalid_ptrace_v_csr(struct __riscv_v_ext_state *vstate,
+				struct __riscv_v_regset_state *ptrace)
+{
+	unsigned long vsew, vlmul, vfrac, vl;
+	unsigned long elen, vlen;
+	unsigned long sew, lmul;
+	unsigned long reserved;
+
+	if (!has_vector())
+		return 1;
+
+	vlen = vstate->vlenb * 8;
+	if (vstate->vlenb != ptrace->vlenb)
+		return 1;
+
+	reserved = ~(CSR_VXSAT_MASK | (CSR_VXRM_MASK << CSR_VXRM_SHIFT));
+	if (ptrace->vcsr & reserved)
+		return 1;
+
+	/* do not allow to set vill */
+	reserved = ~(VTYPE_VSEW | VTYPE_VLMUL | VTYPE_VMA | VTYPE_VTA);
+	if (ptrace->vtype & reserved)
+		return 1;
+
+	elen = riscv_has_extension_unlikely(RISCV_ISA_EXT_ZVE64X) ? 64 : 32;
+	vsew = (ptrace->vtype & VTYPE_VSEW) >> VTYPE_VSEW_SHIFT;
+	sew = 8 << vsew;
+
+	if (sew > elen)
+		return 1;
+
+	vfrac = (ptrace->vtype & VTYPE_VLMUL_FRAC);
+	vlmul = (ptrace->vtype & VTYPE_VLMUL);
+
+	/* RVV 1.0 spec 3.4.2: VLMUL(0x4) reserved */
+	if (vlmul == 4)
+		return 1;
+
+	/* RVV 1.0 spec 3.4.2: (LMUL < SEW_min / ELEN) reserved */
+	if (vlmul == 5 && elen == 32)
+		return 1;
+
+	/* for zero vl verify that at least one element is possible */
+	vl = ptrace->vl ? ptrace->vl : 1;
+
+	if (vfrac) {
+		/* integer 1/LMUL: VL =< VLMAX = VLEN / SEW / LMUL */
+		lmul = 2 << (3 - (vlmul - vfrac));
+		if (vlen < vl * sew * lmul)
+			return 1;
+	} else {
+		/* integer LMUL: VL =< VLMAX = LMUL * VLEN / SEW */
+		lmul = 1 << vlmul;
+		if (vl * sew > lmul * vlen)
+			return 1;
+	}
+
+	return 0;
+}
+
 static int riscv_vr_set(struct task_struct *target,
 			const struct user_regset *regset,
 			unsigned int pos, unsigned int count,
@@ -145,7 +205,7 @@ static int riscv_vr_set(struct task_struct *target,
 	if (unlikely(ret))
 		return ret;
 
-	if (vstate->vlenb != ptrace_vstate.vlenb)
+	if (invalid_ptrace_v_csr(vstate, &ptrace_vstate))
 		return -EINVAL;
 
 	vstate->vstart = ptrace_vstate.vstart;
-- 
2.51.0


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