[PATCH v2 0/2] ima/evm: Ensure digest to verify is in linear mapping area
Roberto Sassu
roberto.sassu at huaweicloud.com
Thu Dec 1 10:06:23 UTC 2022
From: Roberto Sassu <roberto.sassu at huawei.com>
As sg_set_buf() requires the buffer for a crypto operation to be in the
linear mapping area, so that it is always in adjacent pages, ensure that
this requirement is met for IMA/EVM.
Currently, evm_verify_hmac() and xattr_verify() put the evm_digest and
ima_max_digest_data structures in the stack. As normally the stack is in
the linear mapping area, passing them to sg_set_buf() would not be a
problem.
However, if CONFIG_VMAP_STACK is enabled, these structures will reside in
the vmalloc area instead. If CONFIG_DEBUG_SG is enabled, the kernel will
panic:
[ 467.077359] kernel BUG at include/linux/scatterlist.h:163!
[ 467.077939] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
[...]
[ 467.095225] Call Trace:
[ 467.096088] <TASK>
[ 467.096928] ? rcu_read_lock_held_common+0xe/0x50
[ 467.097569] ? rcu_read_lock_sched_held+0x13/0x70
[ 467.098123] ? trace_hardirqs_on+0x2c/0xd0
[ 467.098647] ? public_key_verify_signature+0x470/0x470
[ 467.099237] asymmetric_verify+0x14c/0x300
[ 467.099869] evm_verify_hmac+0x245/0x360
[ 467.100391] evm_inode_setattr+0x43/0x190
To overcome this problem, dynamically allocate the structures with
kmalloc() if CONFIG_VMAP_STACK is enabled, so that they are placed in the
linear mapping area, and use them instead of the in-stack counterparts.
A test report is available here:
https://github.com/robertosassu/ima-evm-utils/actions/runs/3590837109/jobs/6045608579
which contains the following test (include tests for EVM portable
signatures and IMA verity signatures):
https://github.com/robertosassu/ima-evm-utils/commit/41cf11d299e9fc2d13a60dce4b275c2675d9cc23
Changelog:
v1:
- Dynamically allocate the data structures in IMA and EVM, when necessary,
instead of always making a copy in asymmetric_verify() (suggested by
Mimi)
Roberto Sassu (2):
evm: Alloc evm_digest in evm_verify_hmac() if CONFIG_VMAP_STACK=y
ima: Alloc ima_max_digest_data in xattr_verify() if
CONFIG_VMAP_STACK=y
security/integrity/evm/evm_main.c | 26 +++++++++++++++++++++-----
security/integrity/ima/ima_appraise.c | 19 ++++++++++++++++---
2 files changed, 37 insertions(+), 8 deletions(-)
--
2.25.1
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