plugins: Add enforcement of QEMU_PLUGIN_CB flags in register R/W callbacks

This patch adds functionality to enforce the requested QEMU_PLUGIN_CB_
flags level passed when registering a callback function using the
plugins API. Each time a callback is about to be invoked, a thread-local
variable will be updated with the level that callback requested. Then,
called API functions (in particular, the register read and write API)
will call qemu_plugin_get_cb_flags() to check the level is at least the
level they require.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Rowan Hart <rowanbhart@gmail.com>
Message-ID: <20250624175351.440780-4-rowanbhart@gmail.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-ID: <20250627112512.1880708-8-alex.bennee@linaro.org>

1 files changed, 33 insertions, 0 deletions

diff --git a/plugins/core.c b/plugins/core.c
index eb9281fe54..c6e9ef1478 100644
--- a/plugins/core.c
+++ b/plugins/core.c
@@ -15,6 +15,7 @@
 #include "qemu/lockable.h"
 #include "qemu/option.h"
 #include "qemu/plugin.h"
+#include "qemu/qemu-plugin.h"
 #include "qemu/queue.h"
 #include "qemu/rcu_queue.h"
 #include "qemu/rcu.h"
@@ -266,7 +267,9 @@ static void qemu_plugin_vcpu_init__async(CPUState *cpu, run_on_cpu_data unused)
     plugin_grow_scoreboards__locked(cpu);
     qemu_rec_mutex_unlock(&plugin.lock);
 
+    qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_RW_REGS);
     plugin_vcpu_cb__simple(cpu, QEMU_PLUGIN_EV_VCPU_INIT);
+    qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_NO_REGS);
 }
 
 void qemu_plugin_vcpu_init_hook(CPUState *cpu)
@@ -279,7 +282,9 @@ void qemu_plugin_vcpu_exit_hook(CPUState *cpu)
 {
     bool success;
 
+    qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_RW_REGS);
     plugin_vcpu_cb__simple(cpu, QEMU_PLUGIN_EV_VCPU_EXIT);
+    qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_NO_REGS);
 
     assert(cpu->cpu_index != UNASSIGNED_CPU_INDEX);
     qemu_rec_mutex_lock(&plugin.lock);
@@ -367,6 +372,7 @@ void plugin_register_dyn_cb__udata(GArray **arr,
     static TCGHelperInfo info[3] = {
         [QEMU_PLUGIN_CB_NO_REGS].flags = TCG_CALL_NO_RWG,
         [QEMU_PLUGIN_CB_R_REGS].flags = TCG_CALL_NO_WG,
+        [QEMU_PLUGIN_CB_RW_REGS].flags = 0,
         /*
          * Match qemu_plugin_vcpu_udata_cb_t:
          *   void (*)(uint32_t, void *)
@@ -396,6 +402,7 @@ void plugin_register_dyn_cond_cb__udata(GArray **arr,
     static TCGHelperInfo info[3] = {
         [QEMU_PLUGIN_CB_NO_REGS].flags = TCG_CALL_NO_RWG,
         [QEMU_PLUGIN_CB_R_REGS].flags = TCG_CALL_NO_WG,
+        [QEMU_PLUGIN_CB_RW_REGS].flags = 0,
         /*
          * Match qemu_plugin_vcpu_udata_cb_t:
          *   void (*)(uint32_t, void *)
@@ -434,6 +441,7 @@ void plugin_register_vcpu_mem_cb(GArray **arr,
     static TCGHelperInfo info[3] = {
         [QEMU_PLUGIN_CB_NO_REGS].flags = TCG_CALL_NO_RWG,
         [QEMU_PLUGIN_CB_R_REGS].flags = TCG_CALL_NO_WG,
+        [QEMU_PLUGIN_CB_RW_REGS].flags = 0,
         /*
          * Match qemu_plugin_vcpu_mem_cb_t:
          *   void (*)(uint32_t, qemu_plugin_meminfo_t, uint64_t, void *)
@@ -473,7 +481,9 @@ void qemu_plugin_tb_trans_cb(CPUState *cpu, struct qemu_plugin_tb *tb)
     QLIST_FOREACH_SAFE_RCU(cb, &plugin.cb_lists[ev], entry, next) {
         qemu_plugin_vcpu_tb_trans_cb_t func = cb->f.vcpu_tb_trans;
 
+        qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_RW_REGS);
         func(cb->ctx->id, tb);
+        qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_NO_REGS);
     }
 }
 
@@ -498,7 +508,9 @@ qemu_plugin_vcpu_syscall(CPUState *cpu, int64_t num, uint64_t a1, uint64_t a2,
     QLIST_FOREACH_SAFE_RCU(cb, &plugin.cb_lists[ev], entry, next) {
         qemu_plugin_vcpu_syscall_cb_t func = cb->f.vcpu_syscall;
 
+        qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_RW_REGS);
         func(cb->ctx->id, cpu->cpu_index, num, a1, a2, a3, a4, a5, a6, a7, a8);
+        qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_NO_REGS);
     }
 }
 
@@ -520,7 +532,9 @@ void qemu_plugin_vcpu_syscall_ret(CPUState *cpu, int64_t num, int64_t ret)
     QLIST_FOREACH_SAFE_RCU(cb, &plugin.cb_lists[ev], entry, next) {
         qemu_plugin_vcpu_syscall_ret_cb_t func = cb->f.vcpu_syscall_ret;
 
+        qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_RW_REGS);
         func(cb->ctx->id, cpu->cpu_index, num, ret);
+        qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_NO_REGS);
     }
 }
 
@@ -528,14 +542,18 @@ void qemu_plugin_vcpu_idle_cb(CPUState *cpu)
 {
     /* idle and resume cb may be called before init, ignore in this case */
     if (cpu->cpu_index < plugin.num_vcpus) {
+        qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_RW_REGS);
         plugin_vcpu_cb__simple(cpu, QEMU_PLUGIN_EV_VCPU_IDLE);
+        qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_NO_REGS);
     }
 }
 
 void qemu_plugin_vcpu_resume_cb(CPUState *cpu)
 {
     if (cpu->cpu_index < plugin.num_vcpus) {
+        qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_RW_REGS);
         plugin_vcpu_cb__simple(cpu, QEMU_PLUGIN_EV_VCPU_RESUME);
+        qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_NO_REGS);
     }
 }
 
@@ -615,9 +633,13 @@ void qemu_plugin_vcpu_mem_cb(CPUState *cpu, uint64_t vaddr,
         switch (cb->type) {
         case PLUGIN_CB_MEM_REGULAR:
             if (rw & cb->regular.rw) {
+                qemu_plugin_set_cb_flags(cpu,
+                    tcg_call_to_qemu_plugin_cb_flags(cb->regular.info->flags));
+
                 cb->regular.f.vcpu_mem(cpu->cpu_index,
                                        make_plugin_meminfo(oi, rw),
                                        vaddr, cb->regular.userp);
+                qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_NO_REGS);
             }
             break;
         case PLUGIN_CB_INLINE_ADD_U64:
@@ -760,3 +782,14 @@ void plugin_scoreboard_free(struct qemu_plugin_scoreboard *score)
     g_array_free(score->data, TRUE);
     g_free(score);
 }
+
+enum qemu_plugin_cb_flags tcg_call_to_qemu_plugin_cb_flags(int flags)
+{
+    if (flags & TCG_CALL_NO_RWG) {
+        return QEMU_PLUGIN_CB_NO_REGS;
+    } else if (flags & TCG_CALL_NO_WG) {
+        return QEMU_PLUGIN_CB_R_REGS;
+    } else {
+        return QEMU_PLUGIN_CB_RW_REGS;
+    }
+}