Re: [RFC PATCH v9 06/16] ipe: add LSM hooks on execution and kernel read

[Roberto Sassu]

On Mon, 2023-01-30 at 14:57 -0800, Fan Wu wrote:
> From: Deven Bowers <deven.desai@xxxxxxxxxxxxxxxxxxx>
> 
> 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
> ---
>  security/ipe/hooks.c | 169 +++++++++++++++++++++++++++++++++++++++++++
>  security/ipe/hooks.h |  13 ++++
>  security/ipe/ipe.c   |   6 ++
>  3 files changed, 188 insertions(+)
> 
> diff --git a/security/ipe/hooks.c b/security/ipe/hooks.c
> index 335b773c7ae1..fd5109e29c76 100644
> --- a/security/ipe/hooks.c
> +++ b/security/ipe/hooks.c
> @@ -23,3 +23,172 @@ void ipe_sb_free_security(struct super_block *mnt_sb)
>  {
>  	ipe_invalidate_pinned_sb(mnt_sb);
>  }
> +
> +/**
> + * ipe_bprm_check_security - ipe security hook function for bprm check.
> + * @bprm: Supplies a pointer to a linux_binprm structure to source the file
> + *	  being evaluated.
> + *
> + * This LSM hook is called when a binary is loaded through the exec
> + * family of system calls.
> + * Return:
> + * *0	- OK
> + * *!0	- Error
> + */
> +int ipe_bprm_check_security(struct linux_binprm *bprm)
> +{
> +	struct ipe_eval_ctx ctx = { 0 };
> +
> +	build_eval_ctx(&ctx, bprm->file, ipe_op_exec);
> +	return ipe_evaluate_event(&ctx);
> +}
> +
> +/**
> + * ipe_mmap_file - ipe security hook function for mmap check.
> + * @f: File being mmap'd. Can be NULL in the case of anonymous memory.
> + * @reqprot: The requested protection on the mmap, passed from usermode.
> + * @prot: The effective protection on the mmap, resolved from reqprot and
> + *	  system configuration.
> + * @flags: Unused.
> + *
> + * This hook is called when a file is loaded through the mmap
> + * family of system calls.
> + *
> + * Return:
> + * * 0	- OK
> + * * !0	- Error
> + */
> +int ipe_mmap_file(struct file *f, unsigned long reqprot, unsigned long prot,
> +		  unsigned long flags)
> +{
> +	struct ipe_eval_ctx ctx = { 0 };
> +
> +	if (prot & PROT_EXEC || reqprot & PROT_EXEC) {

Since the kernel only adds flags and doesn't clear them, isn't safe to
just consider prot? Oh, you mentioned it in the changelog, maybe just
for ipe_file_mprotect().

> +		build_eval_ctx(&ctx, f, ipe_op_exec);
> +		return ipe_evaluate_event(&ctx);
> +	}

Uhm, I think some considerations that IMA does for mmap() are relevant
also for IPE.

For example, look at mmap_violation_check(). It checks if there are
writable mappings, and if yes, it denies the access.

Similarly for mprotect(), is adding PROT_EXEC safe?

> +
> +	return 0;
> +}
> +
> +/**
> + * ipe_file_mprotect - ipe security hook function for mprotect check.
> + * @vma: Existing virtual memory area created by mmap or similar.
> + * @reqprot: The requested protection on the mmap, passed from usermode.
> + * @prot: The effective protection on the mmap, resolved from reqprot and
> + *	  system configuration.
> + *
> + * This LSM hook is called when a mmap'd region of memory is changing
> + * its protections via mprotect.
> + *
> + * Return:
> + * * 0	- OK
> + * * !0	- Error
> + */
> +int ipe_file_mprotect(struct vm_area_struct *vma, unsigned long reqprot,
> +		      unsigned long prot)
> +{
> +	struct ipe_eval_ctx ctx = { 0 };
> +
> +	/* Already Executable */
> +	if (vma->vm_flags & VM_EXEC)
> +		return 0;
> +
> +	if (prot & PROT_EXEC) {
> +		build_eval_ctx(&ctx, vma->vm_file, ipe_op_exec);
> +		return ipe_evaluate_event(&ctx);
> +	}
> +
> +	return 0;
> +}
> +
> +/**
> + * 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;
> +
> +	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_max;
> +		WARN(op == ipe_op_max, "no rule setup for enum %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 = { 0 };
> +
> +	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_max;
> +		WARN(op == ipe_op_max, "no rule setup for enum %d", id);
> +	}
> +
> +	build_eval_ctx(&ctx, NULL, op);
> +	return ipe_evaluate_event(&ctx);
> +}
> diff --git a/security/ipe/hooks.h b/security/ipe/hooks.h
> index 30fe455389bf..857cae69678c 100644
> --- a/security/ipe/hooks.h
> +++ b/security/ipe/hooks.h
> @@ -11,4 +11,17 @@
>  
>  void ipe_sb_free_security(struct super_block *mnt_sb);
>  
> +int ipe_bprm_check_security(struct linux_binprm *bprm);
> +
> +int ipe_mmap_file(struct file *f, unsigned long reqprot, unsigned long prot,
> +		  unsigned long flags);
> +
> +int ipe_file_mprotect(struct vm_area_struct *vma, unsigned long reqprot,
> +		      unsigned long prot);
> +
> +int ipe_kernel_read_file(struct file *file, enum kernel_read_file_id id,
> +			 bool contents);
> +
> +int ipe_kernel_load_data(enum kernel_load_data_id id, bool contents);
> +
>  #endif /* IPE_HOOKS_H */
> diff --git a/security/ipe/ipe.c b/security/ipe/ipe.c
> index bef923026b50..7af2f942decd 100644
> --- a/security/ipe/ipe.c
> +++ b/security/ipe/ipe.c
> @@ -4,6 +4,7 @@
>   */
>  
>  #include "ipe.h"
> +#include "hooks.h"
>  
>  bool ipe_enabled;
>  
> @@ -12,6 +13,11 @@ static struct lsm_blob_sizes ipe_blobs __lsm_ro_after_init = {
>  
>  static struct security_hook_list ipe_hooks[] __lsm_ro_after_init = {
>  	LSM_HOOK_INIT(sb_free_security, ipe_sb_free_security),
> +	LSM_HOOK_INIT(bprm_check_security, ipe_bprm_check_security),
> +	LSM_HOOK_INIT(mmap_file, ipe_mmap_file),
> +	LSM_HOOK_INIT(file_mprotect, ipe_file_mprotect),
> +	LSM_HOOK_INIT(kernel_read_file, ipe_kernel_read_file),
> +	LSM_HOOK_INIT(kernel_load_data, ipe_kernel_load_data),
>  };

Uhm, maybe I would incorporate patch 1 with this.

Roberto