Re: [PATCH RFC v11 4/19] ipe: add LSM hooks on execution and kernel read

[Paul Moore]

On Oct  4, 2023 Fan Wu <wufan@xxxxxxxxxxxxxxxxxxx> wrote:
> 
> IPE's initial goal is to control both execution and the loading of
> kernel modules based on the system's definition of trust. It
> accomplishes this by plugging into the security hooks for
> bprm_check_security, file_mprotect, mmap_file, kernel_load_data,
> and kernel_read_data.
> 
> Signed-off-by: Deven Bowers <deven.desai@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Fan Wu <wufan@xxxxxxxxxxxxxxxxxxx>
> ---
> v2:
>   + Split evaluation loop, access control hooks,
>     and evaluation loop from policy parser and userspace
>     interface to pass mailing list character limit
> 
> v3:
>   + Move ipe_load_properties to patch 04.
>   + Remove useless 0-initializations
>   + Prefix extern variables with ipe_
>   + Remove kernel module parameters, as these are
>     exposed through sysctls.
>   + Add more prose to the IPE base config option
>     help text.
>   + Use GFP_KERNEL for audit_log_start.
>   + Remove unnecessary caching system.
>   + Remove comments from headers
>   + Use rcu_access_pointer for rcu-pointer null check
>   + Remove usage of reqprot; use prot only.
>   + Move policy load and activation audit event to 03/12
> 
> v4:
>   + Remove sysctls in favor of securityfs nodes
>   + Re-add kernel module parameters, as these are now
>     exposed through securityfs.
>   + Refactor property audit loop to a separate function.
> 
> v5:
>   + fix minor grammatical errors
>   + do not group rule by curly-brace in audit record,
>     reconstruct the exact rule.
> 
> v6:
>   + No changes
> 
> v7:
>   + Further split lsm creation, the audit system, the evaluation loop
>     and access control hooks into separate commits.
> 
> v8:
>   + Rename hook functions to follow the lsmname_hook_name convention
>   + Remove ipe_hook enumeration, can be derived from correlation with
>     syscall audit record.
> 
> v9:
>   + Minor changes for adapting to the new parser
> 
> v10:
>   + Remove @reqprot part
> 
> v11:
>   + Fix code style issues
> ---
>  security/ipe/Makefile |   1 +
>  security/ipe/eval.c   |  14 ++++
>  security/ipe/eval.h   |   3 +
>  security/ipe/hooks.c  | 183 ++++++++++++++++++++++++++++++++++++++++++
>  security/ipe/hooks.h  |  25 ++++++
>  security/ipe/ipe.c    |   6 ++
>  6 files changed, 232 insertions(+)
>  create mode 100644 security/ipe/hooks.c
>  create mode 100644 security/ipe/hooks.h

...

> diff --git a/security/ipe/hooks.c b/security/ipe/hooks.c
> new file mode 100644
> index 000000000000..6164a9b53361
> --- /dev/null
> +++ b/security/ipe/hooks.c
> @@ -0,0 +1,183 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) Microsoft Corporation. All rights reserved.
> + */

...

> +/**
> + * ipe_kernel_read_file - ipe security hook function for kernel read.
> + * @file: Supplies a pointer to the file structure being read in from disk.
> + * @id: Supplies the enumeration identifying the purpose of the read.
> + * @contents: Unused.
> + *
> + * This LSM hook is called when a file is being read in from disk from
> + * the kernel.
> + *
> + * Return:
> + * 0 - OK
> + * !0 - Error
> + */
> +int ipe_kernel_read_file(struct file *file, enum kernel_read_file_id id,
> +			 bool contents)
> +{
> +	enum ipe_op_type op;
> +	struct ipe_eval_ctx ctx = IPE_EVAL_CTX_INIT;
> +
> +	switch (id) {
> +	case READING_FIRMWARE:
> +		op = IPE_OP_FIRMWARE;
> +		break;
> +	case READING_MODULE:
> +		op = IPE_OP_KERNEL_MODULE;
> +		break;
> +	case READING_KEXEC_INITRAMFS:
> +		op = IPE_OP_KEXEC_INITRAMFS;
> +		break;
> +	case READING_KEXEC_IMAGE:
> +		op = IPE_OP_KEXEC_IMAGE;
> +		break;
> +	case READING_POLICY:
> +		op = IPE_OP_IMA_POLICY;
> +		break;
> +	case READING_X509_CERTIFICATE:
> +		op = IPE_OP_IMA_X509;
> +		break;
> +	default:
> +		op = IPE_OP_INVALID;
> +		WARN(op == IPE_OP_INVALID, "no rule setup for enum %d", id);

I'm not sure you need to test @op above since you set @op on the line
above, just use true/1 to simplify things.  It also seems like it
might be helpful to provice some context for the enum above in the
WARN() message.  For example:

  WARN(1, "no rule setup for kernel_read_file %d", id);

> +	}
> +
> +	build_eval_ctx(&ctx, file, op);
> +	return ipe_evaluate_event(&ctx);
> +}
> +
> +/**
> + * ipe_kernel_load_data - ipe security hook function for kernel load data.
> + * @id: Supplies the enumeration identifying the purpose of the read.
> + * @contents: Unused.
> + *
> + * This LSM hook is called when a buffer is being read in from disk.
> + *
> + * Return:
> + * * 0	- OK
> + * * !0	- Error
> + */
> +int ipe_kernel_load_data(enum kernel_load_data_id id, bool contents)
> +{
> +	enum ipe_op_type op;
> +	struct ipe_eval_ctx ctx = IPE_EVAL_CTX_INIT;
> +
> +	switch (id) {
> +	case LOADING_FIRMWARE:
> +		op = IPE_OP_FIRMWARE;
> +		break;
> +	case LOADING_MODULE:
> +		op = IPE_OP_KERNEL_MODULE;
> +		break;
> +	case LOADING_KEXEC_INITRAMFS:
> +		op = IPE_OP_KEXEC_INITRAMFS;
> +		break;
> +	case LOADING_KEXEC_IMAGE:
> +		op = IPE_OP_KEXEC_IMAGE;
> +		break;
> +	case LOADING_POLICY:
> +		op = IPE_OP_IMA_POLICY;
> +		break;
> +	case LOADING_X509_CERTIFICATE:
> +		op = IPE_OP_IMA_X509;
> +		break;
> +	default:
> +		op = IPE_OP_INVALID;
> +		WARN(op == IPE_OP_INVALID, "no rule setup for enum %d", id);

See my comments in ipe_kernel_read_file(), they also apply here.

> +	}
> +
> +	build_eval_ctx(&ctx, NULL, op);
> +	return ipe_evaluate_event(&ctx);
> +}

--
paul-moore.com