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

Deven Bowers
2021-10-26T19:04:00Z

On 10/25/2021 5:22 AM, Roberto Sassu wrote:
>> From:deven.desai@linux.microsoft.com
>> [mailto:deven.desai@linux.microsoft.com]
>> 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;
> Possible problem here. If someone (like me) adds a new file type
> and forgets to add a case, there will be an out of bound access
> in evaluate():
>
> rules = &pol->parsed->rules[ctx->op];
>
> due to the static definition of the rules array in the ipe_parsed_policy
> structure (array length: ipe_operation_max).

Yeah, that's a problem. I can fix this down in the eval loop by matching
the global default and emitting a WARN here.

> Roberto
>
> HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
> Managing Director: Li Peng, Zhong Ronghua
>
>> + }
>> +
>> + 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),
>> };
>>
>> /**
>> 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 {
>> --
>> 2.33.0