Re: [PATCH v2 1/1] efi_leader: delete rng-seed if having EFI RNG protocol

Hi Heinrich,

On Sat, Sep 14, 2024 at 06:08:12PM +0200, Heinrich Schuchardt wrote:

For measured be boot we must avoid any volatile values in the device-tree. We already delete /chosen/kaslr-seed if we provide and EFI RNG protocol.

Additionally remove /chosen/rng-seed provided by QEMU or U-Boot.

Signed-off-by: Heinrich Schuchardt heinrich.schuchardt@canonical.com

v2: put log_debug() in else branch

---

include/efi_loader.h | 2 +- lib/efi_loader/efi_dt_fixup.c | 16 +++++++++++----- lib/efi_loader/efi_helper.c | 2 +- 3 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/include/efi_loader.h b/include/efi_loader.h index f84852e384f..511281e150e 100644 --- a/include/efi_loader.h +++ b/include/efi_loader.h @@ -567,7 +567,7 @@ efi_status_t EFIAPI efi_convert_pointer(efi_uintn_t debug_disposition, /* Carve out DT reserved memory ranges */ void efi_carve_out_dt_rsv(void *fdt); /* Purge unused kaslr-seed */ -void efi_try_purge_kaslr_seed(void *fdt); +void efi_try_purge_rng_seed(void *fdt); /* Called by bootefi to make console interface available */ efi_status_t efi_console_register(void); /* Called by efi_init_obj_list() to proble all block devices */ diff --git a/lib/efi_loader/efi_dt_fixup.c b/lib/efi_loader/efi_dt_fixup.c index 9d017804eea..b97758d1305 100644 --- a/lib/efi_loader/efi_dt_fixup.c +++ b/lib/efi_loader/efi_dt_fixup.c @@ -41,7 +41,7 @@ static void efi_reserve_memory(u64 addr, u64 size, bool nomap) }

/**

• • efi_try_purge_kaslr_seed() - Remove unused kaslr-seed

• • efi_try_purge_rng_seed() - Remove unused kaslr-seed, rng-seed
  • Kernel's EFI STUB only relies on EFI_RNG_PROTOCOL for randomization
  • and completely ignores the kaslr-seed for its own randomness needs

@@ -51,8 +51,9 @@ static void efi_reserve_memory(u64 addr, u64 size, bool nomap)

• @fdt: Pointer to device tree

*/ -void efi_try_purge_kaslr_seed(void *fdt) +void efi_try_purge_rng_seed(void *fdt) {

• const char * const prop[] = {"kaslr-seed", "rng-seed"}; const efi_guid_t efi_guid_rng_protocol = EFI_RNG_PROTOCOL_GUID; struct efi_handler *handler; efi_status_t ret;

@@ -67,9 +68,14 @@ void efi_try_purge_kaslr_seed(void *fdt) if (nodeoff < 0) return;

• err = fdt_delprop(fdt, nodeoff, "kaslr-seed");
• if (err < 0 && err != -FDT_ERR_NOTFOUND)

• log_err("Error deleting kaslr-seed\n");
  

• for (const char * const *pos = prop; pos < &prop[ARRAY_SIZE(prop)];

I think for (int i = 0; i < ARRAY_SIZE(prop); i++) fdt_delprop(fdt, nodeoff, prop[i]);

is a lot easier to read

Other than that, the patch looks fine

Thanks /Ilias

•     ++pos) {
  

• err = fdt_delprop(fdt, nodeoff, *pos);
  

• if (err < 0 && err != -FDT_ERR_NOTFOUND)
  

• 	log_err("Error deleting %s\n", *pos);
  

• else
  

• 	log_debug("Deleted /chosen/%s\n", *pos);
  

• }

}

/** diff --git a/lib/efi_loader/efi_helper.c b/lib/efi_loader/efi_helper.c index 96f847652ec..a481eb4b7e3 100644 --- a/lib/efi_loader/efi_helper.c +++ b/lib/efi_loader/efi_helper.c @@ -522,7 +522,7 @@ efi_status_t efi_install_fdt(void *fdt) /* Create memory reservations as indicated by the device tree */ efi_carve_out_dt_rsv(fdt);

• efi_try_purge_kaslr_seed(fdt);

• efi_try_purge_rng_seed(fdt);

  if (CONFIG_IS_ENABLED(EFI_TCG2_PROTOCOL_MEASURE_DTB)) { ret = efi_tcg2_measure_dtb(fdt);

-- 2.45.2