Re: [RFC PATCH v7 05/16] ipe: add LSM hooks on execution and kernel read

Casey Schaufler
2021-10-13T20:04:41Z

On 10/13/2021 12:06 PM, deven.desai@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 execve,
> mprotect, mmap, kernel_load_data and kernel_read_data.
>
> Signed-off-by: Deven Bowers <deven.desai@linux.microsoft.com>
> ---
>
> Relevant changes since v6:
> * Split up patch 02/12 into four parts:
> 1. context creation [01/16]
> 2. audit [07/16]
> 3. evaluation loop [03/16]
> 4. access control hooks [05/16] (this patch)
>
> ---
> security/ipe/hooks.c | 149 ++++++++++++++++++++++++++++++++++++++++++
> security/ipe/hooks.h | 23 ++++++-
> security/ipe/ipe.c | 5 ++
> security/ipe/policy.c | 23 +++++++
> security/ipe/policy.h | 12 +++-
> 5 files changed, 209 insertions(+), 3 deletions(-)
>
> diff --git a/security/ipe/hooks.c b/security/ipe/hooks.c
> index ed0c886eaa5a..216242408a80 100644
> --- a/security/ipe/hooks.c
> +++ b/security/ipe/hooks.c
> @@ -6,11 +6,15 @@
> #include "ipe.h"
> #include "ctx.h"
> #include "hooks.h"
> +#include "eval.h"
>
> +#include <linux/fs.h>
> #include <linux/sched.h>
> #include <linux/types.h>
> #include <linux/refcount.h>
> #include <linux/rcupdate.h>
> +#include <linux/binfmts.h>
> +#include <linux/mman.h>
>
> /**
> * ipe_task_alloc: Assign a new context for an associated task structure.
> @@ -56,3 +60,148 @@ void ipe_task_free(struct task_struct *task)
> ipe_put_ctx(ctx);
> rcu_read_unlock();
> }
> +
> +/**
> + * ipe_on_exec: LSM hook called when a process is loaded through the exec
> + * family of system calls.
> + * @bprm: Supplies a pointer to a linux_binprm structure to source the file
> + * being evaluated.
> + *
> + * Return:
> + * 0 - OK
> + * !0 - Error
> + */
> +int ipe_on_exec(struct linux_binprm *bprm)
> +{
> + return ipe_process_event(bprm->file, ipe_operation_exec, ipe_hook_exec);
> +}
> +
> +/**
> + * ipe_on_mmap: LSM hook called when a file is loaded through the mmap
> + * family of system calls.
> + * @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.
> + *
> + * Return:
> + * 0 - OK
> + * !0 - Error
> + */
> +int ipe_on_mmap(struct file *f, unsigned long reqprot, unsigned long prot,
> + unsigned long flags)
> +{
> + if (prot & PROT_EXEC || reqprot & PROT_EXEC)
> + return ipe_process_event(f, ipe_operation_exec, ipe_hook_mmap);
> +
> + return 0;
> +}
> +
> +/**
> + * ipe_on_mprotect: LSM hook called when a mmap'd region of memory is changing
> + * its protections via mprotect.
> + * @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.
> + *
> + * Return:
> + * 0 - OK
> + * !0 - Error
> + */
> +int ipe_on_mprotect(struct vm_area_struct *vma, unsigned long reqprot,
> + unsigned long prot)
> +{
> + /* Already Executable */
> + if (vma->vm_flags & VM_EXEC)
> + return 0;
> +
> + if (((prot & PROT_EXEC) || reqprot & PROT_EXEC))
> + return ipe_process_event(vma->vm_file, ipe_operation_exec,
> + ipe_hook_mprotect);
> +
> + return 0;
> +}
> +
> +/**
> + * ipe_on_kernel_read: LSM hook called when a file is being read in from
> + * disk.
> + * @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.
> + *
> + * Return:
> + * 0 - OK
> + * !0 - Error
> + */
> +int ipe_on_kernel_read(struct file *file, enum kernel_read_file_id id,
> + bool contents)
> +{
> + enum ipe_operation op;
> +
> + switch (id) {
> + case READING_FIRMWARE:
> + op = ipe_operation_firmware;
> + break;
> + case READING_MODULE:
> + op = ipe_operation_kernel_module;
> + break;
> + case READING_KEXEC_INITRAMFS:
> + op = ipe_operation_kexec_initramfs;
> + break;
> + case READING_KEXEC_IMAGE:
> + op = ipe_operation_kexec_image;
> + break;
> + case READING_POLICY:
> + op = ipe_operation_ima_policy;
> + break;
> + case READING_X509_CERTIFICATE:
> + op = ipe_operation_ima_x509;
> + break;
> + default:
> + op = ipe_operation_max;
> + }
> +
> + return ipe_process_event(file, op, ipe_hook_kernel_read);
> +}
> +
> +/**
> + * ipe_on_kernel_load_data: LSM hook called when a buffer is being read in from
> + * disk.
> + * @id: Supplies the enumeration identifying the purpose of the read.
> + * @contents: Unused.
> + *
> + * Return:
> + * 0 - OK
> + * !0 - Error
> + */
> +int ipe_on_kernel_load_data(enum kernel_load_data_id id, bool contents)
> +{
> + enum ipe_operation op;
> +
> + switch (id) {
> + case LOADING_FIRMWARE:
> + op = ipe_operation_firmware;
> + break;
> + case LOADING_MODULE:
> + op = ipe_operation_kernel_module;
> + break;
> + case LOADING_KEXEC_INITRAMFS:
> + op = ipe_operation_kexec_initramfs;
> + break;
> + case LOADING_KEXEC_IMAGE:
> + op = ipe_operation_kexec_image;
> + break;
> + case LOADING_POLICY:
> + op = ipe_operation_ima_policy;
> + break;
> + case LOADING_X509_CERTIFICATE:
> + op = ipe_operation_ima_x509;
> + break;
> + default:
> + op = ipe_operation_max;
> + }
> +
> + return ipe_process_event(NULL, op, ipe_hook_kernel_load);
> +}
> diff --git a/security/ipe/hooks.h b/security/ipe/hooks.h
> index 58ed4a612e26..c99a0b7f45f7 100644
> --- a/security/ipe/hooks.h
> +++ b/security/ipe/hooks.h
> @@ -5,11 +5,19 @@
> #ifndef IPE_HOOKS_H
> #define IPE_HOOKS_H
>
> +#include <linux/fs.h>
> #include <linux/types.h>
> #include <linux/sched.h>
> +#include <linux/binfmts.h>
> +#include <linux/security.h>
>
> enum ipe_hook {
> - ipe_hook_max = 0
> + ipe_hook_exec = 0,
> + ipe_hook_mmap,
> + ipe_hook_mprotect,
> + ipe_hook_kernel_read,
> + ipe_hook_kernel_load,
> + ipe_hook_max
> };
>
> int ipe_task_alloc(struct task_struct *task,
> @@ -17,4 +25,17 @@ int ipe_task_alloc(struct task_struct *task,
>
> void ipe_task_free(struct task_struct *task);
>
> +int ipe_on_exec(struct linux_binprm *bprm);
> +
> +int ipe_on_mmap(struct file *f, unsigned long reqprot, unsigned long prot,
> + unsigned long flags);
> +
> +int ipe_on_mprotect(struct vm_area_struct *vma, unsigned long reqprot,
> + unsigned long prot);
> +
> +int ipe_on_kernel_read(struct file *file, enum kernel_read_file_id id,
> + bool contents);
> +
> +int ipe_on_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 b58b372327a1..3f9d43783293 100644
> --- a/security/ipe/ipe.c
> +++ b/security/ipe/ipe.c
> @@ -25,6 +25,11 @@ struct lsm_blob_sizes ipe_blobs __lsm_ro_after_init = {
> static struct security_hook_list ipe_hooks[] __lsm_ro_after_init = {
> LSM_HOOK_INIT(task_alloc, ipe_task_alloc),
> LSM_HOOK_INIT(task_free, ipe_task_free),
> + LSM_HOOK_INIT(bprm_check_security, ipe_on_exec),
> + LSM_HOOK_INIT(mmap_file, ipe_on_mmap),
> + LSM_HOOK_INIT(file_mprotect, ipe_on_mprotect),
> + LSM_HOOK_INIT(kernel_read_file, ipe_on_kernel_read),
> + LSM_HOOK_INIT(kernel_load_data, ipe_on_kernel_load_data),

Please stick with the lsmname_hook_name convention, as you did
with ipe_task_alloc and ipe_task_free. Anyone who is looking at
more than one LSM is going to have a much harder time working
with your code the way you have it. Think

% find security | xargs grep '_bprm_check_security('

> };
>
> /**
> diff --git a/security/ipe/policy.c b/security/ipe/policy.c
> index b766824cc08f..048500229365 100644
> --- a/security/ipe/policy.c
> +++ b/security/ipe/policy.c
> @@ -483,6 +483,14 @@ int ipe_parse_op(const struct ipe_policy_token *tok,
> {
> substring_t match[MAX_OPT_ARGS] = { 0 };
> const match_table_t ops = {
> + { ipe_operation_exec, "EXECUTE" },
> + { ipe_operation_firmware, "FIRMWARE" },
> + { ipe_operation_kernel_module, "KMODULE" },
> + { ipe_operation_kexec_image, "KEXEC_IMAGE" },
> + { ipe_operation_kexec_initramfs, "KEXEC_INITRAMFS"},
> + { ipe_operation_ima_policy, "IMA_POLICY" },
> + { ipe_operation_ima_x509, "IMA_X509_CERT" },
> + { ipe_op_alias_kernel_read, "KERNEL_READ" },
> { ipe_op_alias_max, NULL },
> };
>
> @@ -838,6 +846,15 @@ static int parse_policy(struct ipe_policy *p)
> return rc;
> }
>
> +static const enum ipe_operation alias_kread[] = {
> + ipe_operation_firmware,
> + ipe_operation_kernel_module,
> + ipe_operation_ima_policy,
> + ipe_operation_ima_x509,
> + ipe_operation_kexec_image,
> + ipe_operation_kexec_initramfs,
> +};
> +
> /**
> * ipe_is_op_alias: Determine if @op is an alias for one or more operations
> * @op: Supplies the operation to check. Should be either ipe_operation or
> @@ -852,9 +869,15 @@ static int parse_policy(struct ipe_policy *p)
> bool ipe_is_op_alias(int op, const enum ipe_operation **map, size_t *size)
> {
> switch (op) {
> + case ipe_op_alias_kernel_read:
> + *map = alias_kread;
> + *size = ARRAY_SIZE(alias_kread);
> + break;
> default:
> return false;
> }
> +
> + return true;
> }
>
> /**
> diff --git a/security/ipe/policy.h b/security/ipe/policy.h
> index 6818f6405dd0..ca37af46e5af 100644
> --- a/security/ipe/policy.h
> +++ b/security/ipe/policy.h
> @@ -26,7 +26,14 @@ struct ipe_policy_line {
> struct ipe_module;
>
> enum ipe_operation {
> - ipe_operation_max = 0,
> + ipe_operation_exec = 0,
> + ipe_operation_firmware,
> + ipe_operation_kernel_module,
> + ipe_operation_kexec_image,
> + ipe_operation_kexec_initramfs,
> + ipe_operation_ima_policy,
> + ipe_operation_ima_x509,
> + ipe_operation_max
> };
>
> /*
> @@ -34,7 +41,8 @@ enum ipe_operation {
> * that are just one or more operations under the hood
> */
> enum ipe_op_alias {
> - ipe_op_alias_max = ipe_operation_max,
> + ipe_op_alias_kernel_read = ipe_operation_max,
> + ipe_op_alias_max,
> };
>
> enum ipe_action {