From: Ilias Apalodimas ilias.apalodimas@linaro.org Date: Thu, 16 Dec 2021 16:52:08 +0200
Right now we unconditionally pass a 'kaslr-seed' property to the kernel if the DTB we ended up in EFI includes the entry. However the kernel EFI stub completely ignores it and only relies on EFI_RNG_PROTOCOL. So let's get rid of it unconditionally since it would mess up the (upcoming) DTB TPM measuring as well.
NAK
OpenBSD uses the kaslr-seed property in the bootloader to mix in some additional entropy. (It will also use EFI_RNG_PROTOCOL if it is avilable, but most U-Boot boards don't provide that, or at least not yet).
Even on Linux the EFI stub isn't the only way to load a Linux kernel. You can use a conventional EFI bootloader like grub.
Cheers,
Mark
Signed-off-by: Ilias Apalodimas ilias.apalodimas@linaro.org
cmd/bootefi.c | 2 ++ include/efi_loader.h | 2 ++ lib/efi_loader/efi_dt_fixup.c | 22 ++++++++++++++++++++++ 3 files changed, 26 insertions(+)
diff --git a/cmd/bootefi.c b/cmd/bootefi.c index d77d3b6e943d..25f9bfce9b84 100644 --- a/cmd/bootefi.c +++ b/cmd/bootefi.c @@ -310,6 +310,8 @@ efi_status_t efi_install_fdt(void *fdt) /* Create memory reservations as indicated by the device tree */ efi_carve_out_dt_rsv(fdt);
- efi_purge_kaslr_seed(fdt);
- /* Install device tree as UEFI table */ ret = efi_install_configuration_table(&efi_guid_fdt, fdt); if (ret != EFI_SUCCESS) {
diff --git a/include/efi_loader.h b/include/efi_loader.h index 9dd6c2033634..e560401ac54f 100644 --- a/include/efi_loader.h +++ b/include/efi_loader.h @@ -519,6 +519,8 @@ efi_status_t EFIAPI efi_convert_pointer(efi_uintn_t debug_disposition, void **address); /* Carve out DT reserved memory ranges */ void efi_carve_out_dt_rsv(void *fdt); +/* Purge unused kaslr-seed */ +void efi_purge_kaslr_seed(void *fdt); /* Called by bootefi to make console interface available */ efi_status_t efi_console_register(void); /* Called by bootefi to make all disk storage accessible as EFI objects */ diff --git a/lib/efi_loader/efi_dt_fixup.c b/lib/efi_loader/efi_dt_fixup.c index b6fe5d2e5a34..02f7de73872e 100644 --- a/lib/efi_loader/efi_dt_fixup.c +++ b/lib/efi_loader/efi_dt_fixup.c @@ -40,6 +40,28 @@ static void efi_reserve_memory(u64 addr, u64 size, bool nomap) addr, size); }
+/**
- efi_remove_kaslr_seed() - Removed unused kaslr-seed
- Kernel's EFI STUB only relies on EFI_RNG_PROTOCOL for randomization
- and completely ignores the kaslr-seed. Weed it out from the DTB we
- hand over, which would mess up our DTB TPM measurements as well.
- @fdt: Pointer to device tree
- */
+void efi_purge_kaslr_seed(void *fdt) +{
- int nodeoff = fdt_path_offset(fdt, "/chosen");
- int err = 0;
- if (nodeoff < 0)
return;- err = fdt_delprop(fdt, nodeoff, "kaslr-seed");
- if (err < 0)
log_err("Error deleting kaslr-seed\n");+}
/**
- efi_carve_out_dt_rsv() - Carve out DT reserved memory ranges
-- 2.30.2