Re: [PATCH 3/3] meson: Enable -Wvla

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 21/2/24 17:59, Thomas Huth wrote:
> On 21/02/2024 17.26, Thomas Huth wrote:
>> From: Peter Maydell <peter.maydell@linaro.org>
>>
>> QEMU has historically used variable length arrays only very rarely.
>> Variable length arrays are a potential security issue where an
>> on-stack dynamic allocation isn't correctly size-checked, especially
>> when the size comes from the guest.  (An example problem of this kind
>> from the past is CVE-2021-3527).  Forbidding them entirely is a
>> defensive measure against further bugs of this kind.
>>
>> Enable -Wvla to prevent any new uses from sneaking into the codebase.
>>
>> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
>> Message-ID: <20240125173211.1786196-3-peter.maydell@linaro.org>
>> [thuth: rebased to current master branch]
>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>> ---
>>   meson.build | 1 +
>>   1 file changed, 1 insertion(+)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>

>> diff --git a/meson.build b/meson.build
>> index c1dc83e4c0..0ef1654e86 100644
>> --- a/meson.build
>> +++ b/meson.build
>> @@ -592,6 +592,7 @@ warn_flags = [
>>     '-Wstrict-prototypes',
>>     '-Wtype-limits',
>>     '-Wundef',
>> +  '-Wvla',
>>     '-Wwrite-strings',
>>     # Then disable some undesirable warnings
> 
> Sigh, there's a new warning in the latest master branch:
> 
>   https://gitlab.com/thuth/qemu/-/jobs/6225992174
> 
> Caused by commit d65aba828 ("hw/sparc/leon3: implement multiprocessor")...
> Clément, Philippe, could this maybe be written in a different way that 
> does not trigger a -Wvla warning?

Clément, ResetData::entry isn't used, so we can simplify removing
the whole ResetData structure, but I'm not sure this is intended:

-- >8 --
diff --git a/hw/sparc/leon3.c b/hw/sparc/leon3.c
index 4873b59b6c..1ff6b5d63d 100644
--- a/hw/sparc/leon3.c
+++ b/hw/sparc/leon3.c
@@ -68,14 +68,6 @@
  #define LEON3_APB_PNP_OFFSET (0x800FF000)
  #define LEON3_AHB_PNP_OFFSET (0xFFFFF000)

-typedef struct ResetData {
-    struct CPUResetData {
-        int id;
-        SPARCCPU *cpu;
-    } info[MAX_CPUS];
-    uint32_t entry;             /* save kernel entry in case of reset */
-} ResetData;
-
  static uint32_t *gen_store_u32(uint32_t *code, hwaddr addr, uint32_t val)
  {
      stl_p(code++, 0x82100000); /* mov %g0, %g1                */
@@ -148,17 +140,14 @@ static void write_bootloader(void *ptr, hwaddr 
kernel_addr)

  static void leon3_cpu_reset(void *opaque)
  {
-    struct CPUResetData *info = (struct CPUResetData *) opaque;
-    int id = info->id;
-    ResetData *s = (ResetData *)DO_UPCAST(ResetData, info[id], info);
-    CPUState *cpu = CPU(s->info[id].cpu);
+    CPUState *cpu = opaque;
      CPUSPARCState *env = cpu_env(cpu);

      cpu_reset(cpu);

      cpu->halted = cpu->cpu_index != 0;
-    env->pc = s->entry;
-    env->npc = s->entry + 4;
+    env->pc = LEON3_PROM_OFFSET;
+    env->npc = LEON3_PROM_OFFSET + 4;
  }

  static void leon3_cache_control_int(CPUSPARCState *env)
@@ -259,7 +248,7 @@ static void leon3_generic_hw_init(MachineState *machine)
      ram_addr_t ram_size = machine->ram_size;
      const char *bios_name = machine->firmware ?: LEON3_PROM_FILENAME;
      const char *kernel_filename = machine->kernel_filename;
-    SPARCCPU *cpu;
+    SPARCCPU *cpu[MAX_CPUS];
      CPUSPARCState   *env;
      MemoryRegion *address_space_mem = get_system_memory();
      MemoryRegion *prom = g_new(MemoryRegion, 1);
@@ -267,28 +256,22 @@ static void leon3_generic_hw_init(MachineState 
*machine)
      char       *filename;
      int         bios_size;
      int         prom_size;
-    ResetData  *reset_info;
      DeviceState *dev, *irqmpdev;
      int i;
      AHBPnp *ahb_pnp;
      APBPnp *apb_pnp;

-    reset_info = g_malloc0(sizeof(ResetData));
-
      for (i = 0; i < machine->smp.cpus; i++) {
          /* Init CPU */
-        cpu = SPARC_CPU(object_new(machine->cpu_type));
-        qdev_init_gpio_in_named(DEVICE(cpu), leon3_start_cpu, 
"start_cpu", 1);
-        qdev_init_gpio_in_named(DEVICE(cpu), leon3_set_pil_in, "pil", 1);
-        qdev_realize(DEVICE(cpu), NULL, &error_fatal);
-        env = &cpu->env;
+        cpu[i] = SPARC_CPU(object_new(machine->cpu_type));
+        qdev_init_gpio_in_named(DEVICE(cpu[i]), leon3_start_cpu, 
"start_cpu", 1);
+        qdev_init_gpio_in_named(DEVICE(cpu[i]), leon3_set_pil_in, 
"pil", 1);
+        qdev_realize(DEVICE(cpu[i]), NULL, &error_fatal);
+        env = &cpu[i]->env;

          cpu_sparc_set_id(env, i);

-        /* Reset data */
-        reset_info->info[i].id = i;
-        reset_info->info[i].cpu = cpu;
-        qemu_register_reset(leon3_cpu_reset, &reset_info->info[i]);
+        qemu_register_reset(leon3_cpu_reset, cpu[i]);
      }

      ahb_pnp = GRLIB_AHB_PNP(qdev_new(TYPE_GRLIB_AHB_PNP));
@@ -312,13 +295,12 @@ static void leon3_generic_hw_init(MachineState 
*machine)
      sysbus_realize_and_unref(SYS_BUS_DEVICE(irqmpdev), &error_fatal);

      for (i = 0; i < machine->smp.cpus; i++) {
-        cpu = reset_info->info[i].cpu;
-        env = &cpu->env;
+        env = &cpu[i]->env;
          qdev_connect_gpio_out_named(irqmpdev, "grlib-start-cpu", i,
-                                    qdev_get_gpio_in_named(DEVICE(cpu),
+                                    qdev_get_gpio_in_named(DEVICE(cpu[i]),
 
"start_cpu", 0));
          qdev_connect_gpio_out_named(irqmpdev, "grlib-irq", i,
-                                    qdev_get_gpio_in_named(DEVICE(cpu),
+                                    qdev_get_gpio_in_named(DEVICE(cpu[i]),
                                                             "pil", 0));
          env->irq_manager = irqmpdev;
          env->qemu_irq_ack = leon3_irq_manager;
@@ -396,11 +378,6 @@ static void leon3_generic_hw_init(MachineState 
*machine)
               * bootloader.
               */
              write_bootloader(memory_region_get_ram_ptr(prom), entry);
-            reset_info->entry = LEON3_PROM_OFFSET;
-            for (i = 0; i < machine->smp.cpus; i++) {
-                reset_info->info[i].cpu->env.pc = LEON3_PROM_OFFSET;
-                reset_info->info[i].cpu->env.npc = LEON3_PROM_OFFSET + 4;
-            }
          }
      }
---

Regards,

Phil.