Re: [PATCH v4 6/7] plugins: prohibit writing to read-only registers

["Alex Bennée" <alex.bennee@linaro.org>]

Florian Hofhammer <florian.hofhammer@epfl.ch> writes:

> The opaque register handle encodes whether a register is read-only in
> the lowest bit and prevents writing to the register via the plugin API
> in this case.
>
> Signed-off-by: Florian Hofhammer <florian.hofhammer@epfl.ch>
> ---
>  plugins/api.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/plugins/api.c b/plugins/api.c
> index b2c52d2a09..3a8479ddce 100644
> --- a/plugins/api.c
> +++ b/plugins/api.c
> @@ -424,6 +424,7 @@ static GArray *create_register_handles(GArray *gdbstub_regs)
>      for (int i = 0; i < gdbstub_regs->len; i++) {
>          GDBRegDesc *grd = &g_array_index(gdbstub_regs, GDBRegDesc, i);
>          qemu_plugin_reg_descriptor desc;
> +        gint plugin_ro_bit = 0;
>  
>          /* skip "un-named" regs */
>          if (!grd->name) {
> @@ -431,7 +432,6 @@ static GArray *create_register_handles(GArray *gdbstub_regs)
>          }
>  
>          /* Create a record for the plugin */
> -        desc.handle = GINT_TO_POINTER(grd->gdb_reg + 1);
>          desc.name = g_intern_string(grd->name);
>          desc.is_readonly = false;
>          if (g_strcmp0(desc.name, pc_str) == 0
> @@ -442,7 +442,9 @@ static GArray *create_register_handles(GArray *gdbstub_regs)
>              || g_strcmp0(desc.name, rpc_str) == 0
>             ) {
>              desc.is_readonly = true;
> +            plugin_ro_bit = 1;
>          }
> +        desc.handle = GINT_TO_POINTER((grd->gdb_reg << 1) | plugin_ro_bit);
>          desc.feature = g_intern_string(grd->feature_name);
>          g_array_append_val(find_data, desc);
>      }
> @@ -467,7 +469,7 @@ bool qemu_plugin_read_register(struct qemu_plugin_register *reg,
>          return false;
>      }
>  
> -    return (gdb_read_register(current_cpu, buf, GPOINTER_TO_INT(reg) - 1) > 0);
> +    return (gdb_read_register(current_cpu, buf, GPOINTER_TO_INT(reg) >> 1) > 0);
>  }
>  
>  bool qemu_plugin_write_register(struct qemu_plugin_register *reg,
> @@ -476,11 +478,12 @@ bool qemu_plugin_write_register(struct qemu_plugin_register *reg,
>      g_assert(current_cpu);
>  
>      if (buf->len == 0 || (qemu_plugin_get_cb_flags() != QEMU_PLUGIN_CB_RW_REGS &&
> -                          qemu_plugin_get_cb_flags() != QEMU_PLUGIN_CB_RW_REGS_PC)) {
> +                          qemu_plugin_get_cb_flags() != QEMU_PLUGIN_CB_RW_REGS_PC)
> +        || (GPOINTER_TO_INT(reg) & 1)) {

Maybe this is better as:

      g_assert(GPOINTER_TO_INT(reg) & 1 == 0);

      if (buf->len == 0 || (qemu_plugin_get_cb_flags() != QEMU_PLUGIN_CB_RW_REGS &&...

again the plugin is trying to do something it shouldn't.

>          return false;
>      }
>  
> -    return (gdb_write_register(current_cpu, buf->data, GPOINTER_TO_INT(reg) - 1) > 0);
> +    return (gdb_write_register(current_cpu, buf->data, GPOINTER_TO_INT(reg) >> 1) > 0);
>  }
>  
>  void qemu_plugin_set_pc(uint64_t vaddr)

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro