Re: [PATCH v2 2/4] fdt: kaslr seed from tpm entropy

Hi Sean,

On Tue, 29 Aug 2023 at 14:37, seanedmond@linux.microsoft.com wrote:

From: Dhananjay Phadke dphadke@linux.microsoft.com

Add support for KASLR seed from TPM device. Invokes tpm_get_random() API to read 8-bytes of random bytes for KASLR.

Signed-off-by: Dhananjay Phadke dphadke@linux.microsoft.com Signed-off-by: Drew Kluemke ankluemk@microsoft.com Signed-off-by: Sean Edmond seanedmond@microsoft.com

---

boot/image-fdt.c | 15 +++++++++++++++ common/fdt_support.c | 30 ++++++++++++++++++++++++++++++ include/fdt_support.h | 8 ++++++++ lib/Kconfig | 9 +++++++++ 4 files changed, 62 insertions(+)

diff --git a/boot/image-fdt.c b/boot/image-fdt.c index f10200f647..ed38ed77b9 100644 --- a/boot/image-fdt.c +++ b/boot/image-fdt.c @@ -624,6 +624,21 @@ int image_setup_libfdt(struct bootm_headers *images, void *blob, goto err; }

•   if (IS_ENABLED(CONFIG_KASLR_TPM_SEED)) {
  

•           ofnode root;
  

•           ret = root_ofnode_from_fdt(blob, &root);
  

But can't you drop all this code and use an event spy?

•           if (ret) {
  

•                   printf("ERROR: Unable to get root ofnode\n");
  

•                   goto err;
  

•           }
  

•           ret = fdt_tpm_kaslr_seed(root);
  

This function can have a test.

•           if (ret) {
  

•                   printf("ERROR: fdt fixup KASLR failed: %d\n", ret);
  

•                   goto err;
  

•           }
  

•   }
  

•   fdt_ret = optee_copy_fdt_nodes(blob);
    if (fdt_ret) {
            printf("ERROR: transfer of optee nodes to new fdt failed: %s\n",
  

diff --git a/common/fdt_support.c b/common/fdt_support.c index 52be4375b4..d338fcde54 100644 --- a/common/fdt_support.c +++ b/common/fdt_support.c @@ -13,6 +13,9 @@ #include <mapmem.h> #include <net.h> #include <stdio_dev.h> +#include <tpm_api.h> +#include <dm/device.h> +#include <dm/uclass.h> #include <dm/ofnode.h> #include <linux/ctype.h> #include <linux/types.h> @@ -650,6 +653,33 @@ int fdt_fixup_kaslr_seed(ofnode node, const u8 *seed, int len) return 0; }

+int fdt_tpm_kaslr_seed(ofnode node) +{

•   u8 rand[8] = {0};
  

•   struct udevice *dev;
  

•   int ret;
  

•   ret = uclass_first_device_err(UCLASS_TPM, &dev);
  

•   if (ret) {
  

•           printf("ERROR: Failed to find TPM device\n");
  

•           return ret;
  

•   }
  

•   ret = tpm_get_random(dev, rand, sizeof(rand));
  

•   if (ret) {
  

•           printf("ERROR: TPM GetRandom failed, ret=%d\n", ret);
  

•           return ret;
  

•   }
  

•   ret = fdt_fixup_kaslr_seed(node, rand, sizeof(rand));
  

•   if (ret) {
  

•           printf("ERROR: failed to add kaslr-seed to fdt\n");
  

•           return ret;
  

•   }
  

•   return 0;
  

+}

int fdt_record_loadable(void *blob, u32 index, const char *name, uintptr_t load_addr, u32 size, uintptr_t entry_point, const char *type, const char *os, const char *arch) diff --git a/include/fdt_support.h b/include/fdt_support.h index d967118bed..117ca14ca5 100644 --- a/include/fdt_support.h +++ b/include/fdt_support.h @@ -130,6 +130,14 @@ void fdt_fixup_ethernet(void *fdt); */ int fdt_fixup_kaslr_seed(ofnode node, const u8 *seed, int len);

+/*

• • fdt_add_tpm_kaslr_seed - Add kalsr-seed node in Device tree with random

• •                     bytes from TPM device
    

• • @node: ofnode
• • @eret: 0 for success
• */

+int fdt_tpm_kaslr_seed(ofnode node);

int fdt_find_and_setprop(void *fdt, const char *node, const char *prop, const void *val, int len, int create); void fdt_fixup_qe_firmware(void *fdt); diff --git a/lib/Kconfig b/lib/Kconfig index 3926652db6..1530ef7c86 100644 --- a/lib/Kconfig +++ b/lib/Kconfig @@ -465,6 +465,15 @@ config VPL_TPM for the low-level TPM interface, but only one TPM is supported at a time by the TPM library.

+config KASLR_TPM_SEED

•   bool "Use TPM for KASLR random seed"
  

•   depends on TPM_V1 || TPM_V2
  

•   help
  

•     This enables support for using TPMs as entropy source for KASLR seed
  

•     populated in kernel's device tree. Both TPMv1 and TPMv2 are supported
  

•     for the low-level TPM interface, but only one TPM is supported at
  

•     a time by the library.
  

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2.40.0

Regards, Simon