linux-user/riscv: Fix handling of cpu mask in riscv_hwprobe syscall

The third argument of the syscall contains the size of the
cpu mask in bytes, not bits.  Nor is the size rounded up to
a multiple of sizeof(abi_ulong).

Cc: qemu-stable@nongnu.org
Reported-by: Andreas Schwab <schwab@suse.de>
Fixes: 9e1c7d982d7 ("linux-user/riscv: Add syscall riscv_hwprobe")
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250308225902.1208237-3-richard.henderson@linaro.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

linux-user/syscall.c

@@ -9119,35 +9119,38 @@ static void risc_hwprobe_fill_pairs(CPURISCVState *env,
     }
 }
 
-static int cpu_set_valid(abi_long arg3, abi_long arg4)
+/*
+ * If the cpumask_t of (target_cpus, cpusetsize) cannot be read: -EFAULT.
+ * If the cpumast_t has no bits set: -EINVAL.
+ * Otherwise the cpumask_t contains some bit set: 0.
+ * Unlike the kernel, we do not mask cpumask_t by the set of online cpus,
+ * nor bound the search by cpumask_size().
+ */
+static int nonempty_cpu_set(abi_ulong cpusetsize, abi_ptr target_cpus)
 {
-    int ret, i, tmp;
-    size_t host_mask_size, target_mask_size;
-    unsigned long *host_mask;
-
-    /*
-     * cpu_set_t represent CPU masks as bit masks of type unsigned long *.
-     * arg3 contains the cpu count.
-     */
-    tmp = (8 * sizeof(abi_ulong));
-    target_mask_size = ((arg3 + tmp - 1) / tmp) * sizeof(abi_ulong);
-    host_mask_size = (target_mask_size + (sizeof(*host_mask) - 1)) &
-                     ~(sizeof(*host_mask) - 1);
-
-    host_mask = alloca(host_mask_size);
-
-    ret = target_to_host_cpu_mask(host_mask, host_mask_size,
-                                  arg4, target_mask_size);
-    if (ret != 0) {
-        return ret;
-    }
+    unsigned char *p = lock_user(VERIFY_READ, target_cpus, cpusetsize, 1);
+    int ret = -TARGET_EFAULT;
 
-    for (i = 0 ; i < host_mask_size / sizeof(*host_mask); i++) {
-        if (host_mask[i] != 0) {
-            return 0;
+    if (p) {
+        ret = -TARGET_EINVAL;
+        /*
+         * Since we only care about the empty/non-empty state of the cpumask_t
+         * not the individual bits, we do not need to repartition the bits
+         * from target abi_ulong to host unsigned long.
+         *
+         * Note that the kernel does not round up cpusetsize to a multiple of
+         * sizeof(abi_ulong).  After bounding cpusetsize by cpumask_size(),
+         * it copies exactly cpusetsize bytes into a zeroed buffer.
+         */
+        for (abi_ulong i = 0; i < cpusetsize; ++i) {
+            if (p[i]) {
+                ret = 0;
+                break;
+            }
         }
+        unlock_user(p, target_cpus, 0);
     }
-    return -TARGET_EINVAL;
+    return ret;
 }
 
 static abi_long do_riscv_hwprobe(CPUArchState *cpu_env, abi_long arg1,
@@ -9164,7 +9167,7 @@ static abi_long do_riscv_hwprobe(CPUArchState *cpu_env, abi_long arg1,
 
     /* check cpu_set */
     if (arg3 != 0) {
-        ret = cpu_set_valid(arg3, arg4);
+        ret = nonempty_cpu_set(arg3, arg4);
         if (ret != 0) {
             return ret;
         }