Re: Stalled /dev/tpmr0 when context size increases to support RSA 3072 bit keys

[Stefan Berger <stefanb@linux.ibm.com>]

On 6/16/20 6:30 PM, Stefan Berger wrote:
> I am upgrading libtpms's TPM 2 to support RSA 3072 keys (increase 
> context size to 2680 bytes) and wanted to test an upgrade from 
> previous version (0.7.2) which only supports RSA 2048 keys to this 
> newer version (git master). I tried to run this with clevis setting up 
> automatic decryption via TPM 2, but it doesn't work and it seems the 
> issue is due to a stall of /dev/tpmr0 that doesn't respond anymore.
>
>
> [...]
>
> It's stuck polling on /dev/tpmrm0.
>
>    Any ideas?

It has something to do with the offset parameter and the PAGE_SIZE as a 
limit.

[  842.288597] *offset=0
[  842.295345] *offset=2692
[  842.301011] body_size=2692, *offset=2692, buf_size=4096
[  842.301584] tpm tpm0: tpm2_save_context: out of backing storage
[  842.305463] tpm tpm0: tpm2_commit_space: error -12
[  850.793691] tpm tpm0: A TPM error (459) occurred flushing context

This here fixes it. Any suggestion for a proper fix?

Does it concatenate contexts into this PAGE_SIZE'd buffer?


diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-space.c
index 982d341d8837..b5e7307c7ecd 100644
--- a/drivers/char/tpm/tpm2-space.c
+++ b/drivers/char/tpm/tpm2-space.c
@@ -40,7 +40,7 @@ static void tpm2_flush_sessions(struct tpm_chip *chip, 
struct tpm_space *space)

  int tpm2_init_space(struct tpm_space *space)
  {
-       space->context_buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
+       space->context_buf = kzalloc(3*PAGE_SIZE, GFP_KERNEL);
         if (!space->context_buf)
                 return -ENOMEM;

@@ -123,6 +123,7 @@ static int tpm2_save_context(struct tpm_chip *chip, 
u32 handle, u8 *buf,
         unsigned int body_size;
         int rc;

+printk(KERN_INFO "*offset=%u\n", *offset);
         rc = tpm_buf_init(&tbuf, TPM2_ST_NO_SESSIONS, 
TPM2_CC_CONTEXT_SAVE);
         if (rc)
                 return rc;
@@ -147,6 +148,7 @@ static int tpm2_save_context(struct tpm_chip *chip, 
u32 handle, u8 *buf,

         body_size = tpm_buf_length(&tbuf) - TPM_HEADER_SIZE;
         if ((*offset + body_size) > buf_size) {
+printk(KERN_INFO "body_size=%u, *offset=%u, buf_size=%u\n", body_size, 
*offset, buf_size);
                 dev_warn(&chip->dev, "%s: out of backing storage\n", 
__func__);
                 tpm_buf_destroy(&tbuf);
                 return -ENOMEM;
@@ -311,7 +313,7 @@ int tpm2_prepare_space(struct tpm_chip *chip, struct 
tpm_space *space, u8 *cmd,
                sizeof(space->context_tbl));
         memcpy(&chip->work_space.session_tbl, &space->session_tbl,
                sizeof(space->session_tbl));
-       memcpy(chip->work_space.context_buf, space->context_buf, PAGE_SIZE);
+       memcpy(chip->work_space.context_buf, space->context_buf, 
3*PAGE_SIZE);
         memcpy(chip->work_space.session_buf, space->session_buf, 
PAGE_SIZE);

         rc = tpm2_load_space(chip);
@@ -487,12 +489,13 @@ static int tpm2_save_space(struct tpm_chip *chip)
         int i;
         int rc;

+       printk(KERN_INFO "ARRAY_SIZE(space->context_tbl) = %lu\n", 
ARRAY_SIZE(space->context_tbl));
         for (i = 0, offset = 0; i < ARRAY_SIZE(space->context_tbl); i++) {
                 if (!(space->context_tbl[i] && ~space->context_tbl[i]))
                         continue;

                 rc = tpm2_save_context(chip, space->context_tbl[i],
-                                      space->context_buf, PAGE_SIZE,
+                                      space->context_buf, 3*PAGE_SIZE,
                                        &offset);
                 if (rc == -ENOENT) {
                         space->context_tbl[i] = 0;
@@ -530,6 +533,7 @@ int tpm2_commit_space(struct tpm_chip *chip, struct 
tpm_space *space,
         struct tpm_header *header = buf;
         int rc;

+printk(KERN_INFO "%s:%d\n", __func__, __LINE__);
         if (!space)
                 return 0;

@@ -557,7 +561,7 @@ int tpm2_commit_space(struct tpm_chip *chip, struct 
tpm_space *space,
                sizeof(space->context_tbl));
         memcpy(&space->session_tbl, &chip->work_space.session_tbl,
                sizeof(space->session_tbl));
-       memcpy(space->context_buf, chip->work_space.context_buf, PAGE_SIZE);
+       memcpy(space->context_buf, chip->work_space.context_buf, 
3*PAGE_SIZE);
         memcpy(space->session_buf, chip->work_space.session_buf, 
PAGE_SIZE);

         return 0;