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

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

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.


So here's a simple sequence with added 'set -x' into clevis-encrypt-tpm2 
and clevis-decrypt-tpm2:

All good in the encryption part:

[root@localhost ~]# echo hi | clevis encrypt tpm2 '{"key":"rsa"}' > 
hi-rsa3072.jwe
+ case "$TPM2TOOLS_VERSION" in
+ tpm2_createprimary -Q -C o -g sha256 -G rsa -c 
/tmp/tmp.cqg0DMjuL4/primary.context
+ set +x
+ case "$TPM2TOOLS_VERSION" in
+ tpm2_create -Q -g sha256 -C /tmp/tmp.cqg0DMjuL4/primary.context -u 
/tmp/tmp.cqg0DMjuL4/jwk.pub -r /tmp/tmp.cqg0DMjuL4/jwk.priv -a 
'fixedtpm|fixedparent|noda|adminwithpolicy|userwithauth' -i-
+ set +x

The decryption part stalls:

[root@localhost ~]# clevis decrypt < hi-rsa3072.jwe 2>&1 | tee strace.log
+ case "$TPM2TOOLS_VERSION" in
+ tpm2_createprimary -Q -C o -g sha256 -G rsa -c 
/tmp/tmp.9W2U5Fw8HX/primary.context
+ set +x
+ case "$TPM2TOOLS_VERSION" in
+ tpm2_load -Q -C /tmp/tmp.9W2U5Fw8HX/primary.context -u 
/tmp/tmp.9W2U5Fw8HX/jwk.pub -r /tmp/tmp.9W2U5Fw8HX/jwk.priv -c 
/tmp/tmp.9W2U5Fw8HX/load.context -V
INFO on line: "362" in file: "lib/files.c": Assuming tpm context file
INFO on line: "293" in file: "lib/files.c": load: 
TPMS_CONTEXT->savedHandle: 0x80000000
^Z
[1]+  Stopped                 clevis decrypt < hi-rsa3072.jwe 2>&1 | tee 
strace.log


Note: I put the tool in the background using ctrl-Z and now I can run 
this stalled command and it works!

[root@localhost ~]# tpm2_load -Q -C /tmp/tmp.9W2U5Fw8HX/primary.context 
-u /tmp/tmp.9W2U5Fw8HX/jwk.pub -r /tmp/tmp.9W2U5Fw8HX/jwk.priv -c 
load.context -V
INFO on line: "362" in file: "lib/files.c": Assuming tpm context file
INFO on line: "293" in file: "lib/files.c": load: 
TPMS_CONTEXT->savedHandle: 0x80000000
INFO on line: "190" in file: "lib/files.c": Save 
TPMS_CONTEXT->savedHandle: 0x80000000


I know that the above is stalled because I had strace'd it:

openat(AT_FDCWD, "/dev/tpmrm0", O_RDWR|O_NONBLOCK) = 3

[...]

write(3, "\200\1\0\0\0;\0\0\1v@\0\0\7@\0\0\7\0 
\316)s\332fV_\177\326\303\221#"..., 59) = 59
poll([{fd=3, events=POLLIN}], 1, -1)    = 1 ([{fd=3, revents=POLLIN}])
read(3, "\200\1\0\0\0000\0\0\0\0\2\0\0\0\0 
\303cQ\225\0\235F\4-\225:y\353\254\220\247"..., 4096) = 48
openat(AT_FDCWD, "/tmp/tmp.9WItRVOByv/primary.context", O_RDONLY) = 4
fstat(4, {st_mode=S_IFREG|0644, st_size=3036, ...}) = 0
brk(NULL)                               = 0x55fc8d415000
brk(0x55fc8d436000)                     = 0x55fc8d436000
read(4, 
"\272\334\300\336\0\0\0\1@\0\0\1\200\0\0\0\0\0\0\0\0\0\0B\v\302\0\0\0\0\nr"..., 
4096) = 3036
lseek(4, -3036, SEEK_CUR)               = 0
write(2, "INFO on line: \"362\" in file: \"li"..., 44INFO on line: "362" 
in file: "lib/files.c": ) = 44
write(2, "Assuming tpm context file", 25Assuming tpm context file) = 25
write(2, "\n", 1
)                       = 1
read(4, 
"\272\334\300\336\0\0\0\1@\0\0\1\200\0\0\0\0\0\0\0\0\0\0B\v\302\0\0\0\0\nr"..., 
4096) = 3036
write(2, "INFO on line: \"293\" in file: \"li"..., 44INFO on line: "293" 
in file: "lib/files.c": ) = 44
write(2, "load: TPMS_CONTEXT->savedHandle:"..., 43load: 
TPMS_CONTEXT->savedHandle: 0x80000000) = 43
write(2, "\n", 1
)                       = 1
write(3, 
"\200\1\0\0\n\216\0\0\1a\0\0\0\0\0\0\0B\200\0\0\0@\0\0\1\nr\0@]\234"..., 
2702) = 2702
poll([{fd=3, events=POLLIN}], 1, -1)    = 1 ([{fd=3, revents=POLLIN}])
read(3, "\200\1\0\0\0\16\0\0\0\0\200\377\377\377", 4096) = 14
close(4)                                = 0
getpid()                                = 1591
getpid()                                = 1591
write(3, "\200\2\0\0\1{\0\0\1W\200\377\377\377\0\0\0I\2\0\0\0\0 
\203\33\326qO\214\r\0"..., 379) = 379
poll([{fd=3, events=POLLIN}], 1, -1

It's stuck polling on /dev/tpmrm0.

    Any ideas?


     Stefan