[PATCH v9 3/9] plugins: Add enforcement of QEMU_PLUGIN_CB flags in register R/W callbacks

[Rowan Hart <rowanbhart@gmail.com>]

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.

Signed-off-by: Rowan Hart <rowanbhart@gmail.com>
---
 accel/tcg/plugin-gen.c     | 30 ++++++++++++++++++++++++++++++
 include/hw/core/cpu.h      |  1 +
 include/qemu/plugin.h      |  4 ++++
 include/qemu/qemu-plugin.h |  3 ---
 plugins/api.c              |  4 ++++
 plugins/core.c             | 20 ++++++++++++++++++++
 6 files changed, 59 insertions(+), 3 deletions(-)

diff --git a/accel/tcg/plugin-gen.c b/accel/tcg/plugin-gen.c
index c1da753894..9920381a84 100644
--- a/accel/tcg/plugin-gen.c
+++ b/accel/tcg/plugin-gen.c
@@ -117,10 +117,20 @@ static TCGv_i32 gen_cpu_index(void)
 static void gen_udata_cb(struct qemu_plugin_regular_cb *cb)
 {
     TCGv_i32 cpu_index = gen_cpu_index();
+    enum qemu_plugin_cb_flags cb_flags =
+        tcg_call_to_qemu_plugin_cb_flags(cb->info->flags);
+    TCGv_i32 flags = tcg_constant_i32(cb_flags);
+    TCGv_i32 clear_flags = tcg_constant_i32(QEMU_PLUGIN_CB_NO_REGS);
+    tcg_gen_st_i32(flags, tcg_env,
+           offsetof(CPUState, neg.plugin_cb_flags) - sizeof(CPUState));
     tcg_gen_call2(cb->f.vcpu_udata, cb->info, NULL,
                   tcgv_i32_temp(cpu_index),
                   tcgv_ptr_temp(tcg_constant_ptr(cb->userp)));
+    tcg_gen_st_i32(clear_flags, tcg_env,
+           offsetof(CPUState, neg.plugin_cb_flags) - sizeof(CPUState));
     tcg_temp_free_i32(cpu_index);
+    tcg_temp_free_i32(flags);
+    tcg_temp_free_i32(clear_flags);
 }
 
 static TCGv_ptr gen_plugin_u64_ptr(qemu_plugin_u64 entry)
@@ -173,10 +183,20 @@ static void gen_udata_cond_cb(struct qemu_plugin_conditional_cb *cb)
     tcg_gen_ld_i64(val, ptr, 0);
     tcg_gen_brcondi_i64(cond, val, cb->imm, after_cb);
     TCGv_i32 cpu_index = gen_cpu_index();
+    enum qemu_plugin_cb_flags cb_flags =
+        tcg_call_to_qemu_plugin_cb_flags(cb->info->flags);
+    TCGv_i32 flags = tcg_constant_i32(cb_flags);
+    TCGv_i32 clear_flags = tcg_constant_i32(QEMU_PLUGIN_CB_NO_REGS);
+    tcg_gen_st_i32(flags, tcg_env,
+           offsetof(CPUState, neg.plugin_cb_flags) - sizeof(CPUState));
     tcg_gen_call2(cb->f.vcpu_udata, cb->info, NULL,
                   tcgv_i32_temp(cpu_index),
                   tcgv_ptr_temp(tcg_constant_ptr(cb->userp)));
+    tcg_gen_st_i32(clear_flags, tcg_env,
+           offsetof(CPUState, neg.plugin_cb_flags) - sizeof(CPUState));
     tcg_temp_free_i32(cpu_index);
+    tcg_temp_free_i32(flags);
+    tcg_temp_free_i32(clear_flags);
     gen_set_label(after_cb);
 
     tcg_temp_free_i64(val);
@@ -210,12 +230,22 @@ static void gen_mem_cb(struct qemu_plugin_regular_cb *cb,
                        qemu_plugin_meminfo_t meminfo, TCGv_i64 addr)
 {
     TCGv_i32 cpu_index = gen_cpu_index();
+    enum qemu_plugin_cb_flags cb_flags =
+        tcg_call_to_qemu_plugin_cb_flags(cb->info->flags);
+    TCGv_i32 flags = tcg_constant_i32(cb_flags);
+    TCGv_i32 clear_flags = tcg_constant_i32(QEMU_PLUGIN_CB_NO_REGS);
+    tcg_gen_st_i32(flags, tcg_env,
+           offsetof(CPUState, neg.plugin_cb_flags) - sizeof(CPUState));
     tcg_gen_call4(cb->f.vcpu_mem, cb->info, NULL,
                   tcgv_i32_temp(cpu_index),
                   tcgv_i32_temp(tcg_constant_i32(meminfo)),
                   tcgv_i64_temp(addr),
                   tcgv_ptr_temp(tcg_constant_ptr(cb->userp)));
+    tcg_gen_st_i32(clear_flags, tcg_env,
+           offsetof(CPUState, neg.plugin_cb_flags) - sizeof(CPUState));
     tcg_temp_free_i32(cpu_index);
+    tcg_temp_free_i32(flags);
+    tcg_temp_free_i32(clear_flags);
 }
 
 static void inject_cb(struct qemu_plugin_dyn_cb *cb)
diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
index 1e87f7d393..d3cc9a5224 100644
--- a/include/hw/core/cpu.h
+++ b/include/hw/core/cpu.h
@@ -368,6 +368,7 @@ typedef struct CPUNegativeOffsetState {
     GArray *plugin_mem_cbs;
     uint64_t plugin_mem_value_low;
     uint64_t plugin_mem_value_high;
+    int32_t plugin_cb_flags;
 #endif
     IcountDecr icount_decr;
     bool can_do_io;
diff --git a/include/qemu/plugin.h b/include/qemu/plugin.h
index 9726a9ebf3..2fef2e7d71 100644
--- a/include/qemu/plugin.h
+++ b/include/qemu/plugin.h
@@ -209,6 +209,10 @@ void qemu_plugin_user_prefork_lock(void);
  */
 void qemu_plugin_user_postfork(bool is_child);
 
+enum qemu_plugin_cb_flags tcg_call_to_qemu_plugin_cb_flags(int flags);
+
+enum qemu_plugin_cb_flags qemu_plugin_get_cb_flags(void);
+
 #else /* !CONFIG_PLUGIN */
 
 static inline void qemu_plugin_add_opts(void)
diff --git a/include/qemu/qemu-plugin.h b/include/qemu/qemu-plugin.h
index cfe1692ecb..120fb626a6 100644
--- a/include/qemu/qemu-plugin.h
+++ b/include/qemu/qemu-plugin.h
@@ -254,9 +254,6 @@ typedef struct {
  * @QEMU_PLUGIN_CB_NO_REGS: callback does not access the CPU's regs
  * @QEMU_PLUGIN_CB_R_REGS: callback reads the CPU's regs
  * @QEMU_PLUGIN_CB_RW_REGS: callback reads and writes the CPU's regs
- *
- * Note: currently QEMU_PLUGIN_CB_RW_REGS is unused, plugins cannot change
- * system register state.
  */
 enum qemu_plugin_cb_flags {
     QEMU_PLUGIN_CB_NO_REGS,
diff --git a/plugins/api.c b/plugins/api.c
index 6514f2c76a..3f04399c26 100644
--- a/plugins/api.c
+++ b/plugins/api.c
@@ -437,6 +437,10 @@ int qemu_plugin_read_register(struct qemu_plugin_register *reg, GByteArray *buf)
 {
     g_assert(current_cpu);
 
+    if (qemu_plugin_get_cb_flags() == QEMU_PLUGIN_CB_NO_REGS) {
+        return -1;
+    }
+
     return gdb_read_register(current_cpu, buf, GPOINTER_TO_INT(reg) - 1);
 }
 
diff --git a/plugins/core.c b/plugins/core.c
index eb9281fe54..4fe63472a3 100644
--- a/plugins/core.c
+++ b/plugins/core.c
@@ -367,6 +367,7 @@ 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 +397,7 @@ 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 +436,7 @@ 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 *)
@@ -760,3 +763,20 @@ 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;
+    }
+}
+
+enum qemu_plugin_cb_flags qemu_plugin_get_cb_flags(void)
+{
+    assert(current_cpu);
+    return current_cpu->neg.plugin_cb_flags;
+}
-- 
2.49.0