plugins/core: clamp syscall arguments if target is 32-bit

Syscall arguments are abi_long in user code, and plugin syscall
interface works with uint64_t only.

According to C integer promotion rules, the value is sign extended
before becoming unsigned, thus setting high bits when only 32-bit lower
ones should have a significant value.

As a result, we need to clamp values we receive from user-code
accordingly.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Link: https://lore.kernel.org/qemu-devel/20260305-setpc-v5-v7-1-4c3adba52403@epfl.ch
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>

plugins/core.c

@@ -513,6 +513,23 @@ void qemu_plugin_tb_trans_cb(CPUState *cpu, struct qemu_plugin_tb *tb)
     }
 }
 
+static void clamp_syscall_arguments(uint64_t *a1, uint64_t *a2, uint64_t *a3,
+                                    uint64_t *a4, uint64_t *a5, uint64_t *a6,
+                                    uint64_t *a7, uint64_t *a8)
+{
+    if (target_long_bits() == 32) {
+        const uint64_t mask = UINT32_MAX;
+        *a1 &= mask;
+        *a2 &= mask;
+        *a3 &= mask;
+        *a4 &= mask;
+        *a5 &= mask;
+        *a6 &= mask;
+        *a7 &= mask;
+        *a8 &= mask;
+    }
+}
+
 /*
  * Disable CFI checks.
  * The callback function has been loaded from an external library so we do not
@@ -531,6 +548,8 @@ qemu_plugin_vcpu_syscall(CPUState *cpu, int64_t num, uint64_t a1, uint64_t a2,
         return;
     }
 
+    clamp_syscall_arguments(&a1, &a2, &a3, &a4, &a5, &a6, &a7, &a8);
+
     QLIST_FOREACH_SAFE_RCU(cb, &plugin.cb_lists[ev], entry, next) {
         qemu_plugin_vcpu_syscall_cb_t func = cb->f.vcpu_syscall;
 
@@ -584,6 +603,8 @@ qemu_plugin_vcpu_syscall_filter(CPUState *cpu, int64_t num, uint64_t a1,
         return false;
     }
 
+    clamp_syscall_arguments(&a1, &a2, &a3, &a4, &a5, &a6, &a7, &a8);
+
     qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_RW_REGS);
 
     QLIST_FOREACH_SAFE_RCU(cb, &plugin.cb_lists[ev], entry, next) {