Re: [PATCH v4 08/15] gdb: If enabled, print line used to load EFI kernel symbols when using gdb_grub script

[Daniel Kiper]

Adding Robbie...

Please CC him next time when you post these patches. I would want to
hear his opinion too. Or at least he is aware what is happening here...

On Thu, Dec 15, 2022 at 11:29:31PM -0600, Glenn Washburn wrote:
> If the macro PRINT_GDB_SYM_LOAD_CMD is non-zero, compile code which will
> print the command needed to load symbols for the GRUB EFI kernel. This is
> needed because EFI firmware determines where to load the GRUB EFI at
> runtime, and so the relevant addresses are not known ahead of time.
>
> The command is a custom command defined in the gdb_grub GDB script. So
> GDB should be started with the script as an argument to the -x option or
> sourced into an active GDB session before running the outputted command.

I think this functionality should be disabled when lockdown is enforced,
e.g. on UEFI platforms with Secure Boot enabled.

> Co-developed-by: Peter Jones <pjones@redhat.com>
> Signed-off-by: Glenn Washburn <development@efficientek.com>
> ---
>  config.h.in               |  3 +++
>  grub-core/kern/efi/efi.c  |  4 ++--
>  grub-core/kern/efi/init.c | 19 ++++++++++++++++++-
>  include/grub/efi/efi.h    |  2 +-
>  4 files changed, 24 insertions(+), 4 deletions(-)
>
> diff --git a/config.h.in b/config.h.in
> index 4d1e50eba7..c31eee1bca 100644
> --- a/config.h.in
> +++ b/config.h.in
> @@ -13,6 +13,9 @@
>  #define MM_DEBUG @MM_DEBUG@
>  #endif
>
> +/* Define to 1 to enable printing of gdb command to load module symbols.  */
> +#define PRINT_GDB_SYM_LOAD_CMD 0
> +
>  /* Define to 1 to enable disk cache statistics.  */
>  #define DISK_CACHE_STATS @DISK_CACHE_STATS@
>  #define BOOT_TIME_STATS @BOOT_TIME_STATS@
> diff --git a/grub-core/kern/efi/efi.c b/grub-core/kern/efi/efi.c
> index cf49d6357e..17bd06f7e6 100644
> --- a/grub-core/kern/efi/efi.c
> +++ b/grub-core/kern/efi/efi.c
> @@ -299,7 +299,7 @@ grub_efi_get_variable (const char *var, const 
> grub_efi_guid_t *guid,
>  /* Search the mods section from the PE32/PE32+ image. This code uses
>     a PE32 header, but should work with PE32+ as well.  */
>  grub_addr_t
> -grub_efi_modules_addr (void)
> +grub_efi_section_addr (const char *section_name)
>  {
>    grub_efi_loaded_image_t *image;
>    struct grub_msdos_image_header *header;
> @@ -328,7 +328,7 @@ grub_efi_modules_addr (void)
>         i < coff_header->num_sections;
>         i++, section++)
>      {
> -      if (grub_strcmp (section->name, "mods") == 0)
> +      if (grub_strcmp (section->name, section_name) == 0)
>       break;
>      }
>
> diff --git a/grub-core/kern/efi/init.c b/grub-core/kern/efi/init.c
> index b67bc73a1b..ed3d463c8f 100644
> --- a/grub-core/kern/efi/init.c
> +++ b/grub-core/kern/efi/init.c
> @@ -101,10 +101,24 @@ stack_protector_init (void)
>
>  grub_addr_t grub_modbase;
>
> +#if PRINT_GDB_SYM_LOAD_CMD
> +static void
> +grub_efi_print_gdb_info (void)
> +{
> +  grub_addr_t text;
> +
> +  text = grub_efi_section_addr (".text");
> +  if (!text)
> +    return;
> +
> +  grub_printf ("dynamic_load_symbols %p\n", (void *)text);
> +}
> +#endif
> +
>  void
>  grub_efi_init (void)
>  {
> -  grub_modbase = grub_efi_modules_addr ();
> +  grub_modbase = grub_efi_section_addr ("mods");
>    /* First of all, initialize the console so that GRUB can display
>       messages.  */
>    grub_console_init ();
> @@ -127,6 +141,9 @@ grub_efi_init (void)
>    efi_call_4 (grub_efi_system_table->boot_services->set_watchdog_timer,
>             0, 0, 0, NULL);
>
> +#if PRINT_GDB_SYM_LOAD_CMD
> +  grub_efi_print_gdb_info ();
> +#endif
>    grub_efidisk_init ();
>  }
>
> diff --git a/include/grub/efi/efi.h b/include/grub/efi/efi.h
> index e61272de53..586ac856b5 100644
> --- a/include/grub/efi/efi.h
> +++ b/include/grub/efi/efi.h
> @@ -109,7 +109,7 @@ grub_err_t grub_arch_efi_linux_boot_image(grub_addr_t 
> addr, grub_size_t size,
>                                             char *args);
>  #endif
>
> -grub_addr_t grub_efi_modules_addr (void);
> +grub_addr_t grub_efi_section_addr (const char *section);
>
>  void grub_efi_mm_init (void);
>  void grub_efi_mm_fini (void);

Daniel