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

[Paul Moore <paul@paul-moore.com>]

On Mon, Jan 30, 2023 at 5:59 PM Fan Wu <wufan@linux.microsoft.com> wrote:
>
> From: Deven Bowers <deven.desai@linux.microsoft.com>
>
> 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@linux.microsoft.com>
> Signed-off-by: Fan Wu <wufan@linux.microsoft.com>

...

> ---
>  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) {

Is there a reason why you care about @reqprot?  It seems like IPE
would only be interested in the protection flags that the kernel is
actually using.

I notice that in the `ipe_file_mprotect()` hook you ignore @reqprot,
which I believe is the right thing to do.

> +               build_eval_ctx(&ctx, f, ipe_op_exec);
> +               return ipe_evaluate_event(&ctx);
> +       }
> +
> +       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),
>  };
>
>  /**
> --
> 2.39.0

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