[PATCH v5 05/12] LSM: creation of "check_vmflags" LSM hook
Salvatore Mesoraca
s.mesoraca16 at gmail.com
Sat Jul 6 10:54:46 UTC 2019
Creation of a new LSM hook to check if a given configuration of vmflags,
for a new memory allocation request, should be allowed or not.
It's placed in "do_mmap", "do_brk_flags", "__install_special_mapping"
and "setup_arg_pages".
When loading an ELF, this hook is also used to determine what to do
with an RWE PT_GNU_STACK header. This allows LSM to force the loader
to silently ignore executable stack markings, which is useful a thing to
do when trampoline emulation is available.
Signed-off-by: Salvatore Mesoraca <s.mesoraca16 at gmail.com>
---
fs/binfmt_elf.c | 3 ++-
fs/binfmt_elf_fdpic.c | 3 ++-
fs/exec.c | 4 ++++
include/linux/lsm_hooks.h | 7 +++++++
include/linux/security.h | 6 ++++++
mm/mmap.c | 13 +++++++++++++
security/security.c | 5 +++++
7 files changed, 39 insertions(+), 2 deletions(-)
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 8264b46..1d98737 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -806,7 +806,8 @@ static int load_elf_binary(struct linux_binprm *bprm)
for (i = 0; i < loc->elf_ex.e_phnum; i++, elf_ppnt++)
switch (elf_ppnt->p_type) {
case PT_GNU_STACK:
- if (elf_ppnt->p_flags & PF_X)
+ if (elf_ppnt->p_flags & PF_X &&
+ !security_check_vmflags(VM_EXEC|VM_READ|VM_WRITE))
executable_stack = EXSTACK_ENABLE_X;
else
executable_stack = EXSTACK_DISABLE_X;
diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index d86ebd0d..6e0dee1 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -163,7 +163,8 @@ static int elf_fdpic_fetch_phdrs(struct elf_fdpic_params *params,
if (phdr->p_type != PT_GNU_STACK)
continue;
- if (phdr->p_flags & PF_X)
+ if (phdr->p_flags & PF_X &&
+ !security_check_vmflags(VM_EXEC|VM_READ|VM_WRITE))
params->flags |= ELF_FDPIC_FLAG_EXEC_STACK;
else
params->flags |= ELF_FDPIC_FLAG_NOEXEC_STACK;
diff --git a/fs/exec.c b/fs/exec.c
index 89a500b..abf770a 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -756,6 +756,10 @@ int setup_arg_pages(struct linux_binprm *bprm,
vm_flags |= mm->def_flags;
vm_flags |= VM_STACK_INCOMPLETE_SETUP;
+ ret = security_check_vmflags(vm_flags);
+ if (ret)
+ goto out_unlock;
+
ret = mprotect_fixup(vma, &prev, vma->vm_start, vma->vm_end,
vm_flags);
if (ret)
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 47f58cf..12ce609 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -513,6 +513,11 @@
* @reqprot contains the protection requested by the application.
* @prot contains the protection that will be applied by the kernel.
* Return 0 if permission is granted.
+ * @check_vmflags:
+ * Check if the requested @vmflags are allowed.
+ * @vmflags contains the requested vmflags.
+ * Return 0 if the operation is allowed to continue otherwise return
+ * the appropriate error code.
* @file_lock:
* Check permission before performing file locking operations.
* Note the hook mediates both flock and fcntl style locks.
@@ -1597,6 +1602,7 @@
unsigned long prot, unsigned long flags);
int (*file_mprotect)(struct vm_area_struct *vma, unsigned long reqprot,
unsigned long prot);
+ int (*check_vmflags)(vm_flags_t vmflags);
int (*file_lock)(struct file *file, unsigned int cmd);
int (*file_fcntl)(struct file *file, unsigned int cmd,
unsigned long arg);
@@ -1897,6 +1903,7 @@ struct security_hook_heads {
struct hlist_head mmap_addr;
struct hlist_head mmap_file;
struct hlist_head file_mprotect;
+ struct hlist_head check_vmflags;
struct hlist_head file_lock;
struct hlist_head file_fcntl;
struct hlist_head file_set_fowner;
diff --git a/include/linux/security.h b/include/linux/security.h
index 659071c..aed78eb 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -312,6 +312,7 @@ int security_mmap_file(struct file *file, unsigned long prot,
int security_mmap_addr(unsigned long addr);
int security_file_mprotect(struct vm_area_struct *vma, unsigned long reqprot,
unsigned long prot);
+int security_check_vmflags(vm_flags_t vmflags);
int security_file_lock(struct file *file, unsigned int cmd);
int security_file_fcntl(struct file *file, unsigned int cmd, unsigned long arg);
void security_file_set_fowner(struct file *file);
@@ -859,6 +860,11 @@ static inline int security_file_mprotect(struct vm_area_struct *vma,
return 0;
}
+static inline int security_check_vmflags(vm_flags_t vmflags)
+{
+ return 0;
+}
+
static inline int security_file_lock(struct file *file, unsigned int cmd)
{
return 0;
diff --git a/mm/mmap.c b/mm/mmap.c
index 7e8c3e8a..ec9c0e3d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1390,6 +1390,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
{
struct mm_struct *mm = current->mm;
int pkey = 0;
+ int error;
*populate = 0;
@@ -1453,6 +1454,10 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
vm_flags |= calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
+ error = security_check_vmflags(vm_flags);
+ if (error)
+ return error;
+
if (flags & MAP_LOCKED)
if (!can_do_mlock())
return -EPERM;
@@ -2996,6 +3001,10 @@ static int do_brk_flags(unsigned long addr, unsigned long len, unsigned long fla
return -EINVAL;
flags |= VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;
+ error = security_check_vmflags(flags);
+ if (error)
+ return error;
+
error = get_unmapped_area(NULL, addr, len, 0, MAP_FIXED);
if (offset_in_page(error))
return error;
@@ -3393,6 +3402,10 @@ static struct vm_area_struct *__install_special_mapping(
int ret;
struct vm_area_struct *vma;
+ ret = security_check_vmflags(vm_flags);
+ if (ret)
+ return ERR_PTR(ret);
+
vma = vm_area_alloc(mm);
if (unlikely(vma == NULL))
return ERR_PTR(-ENOMEM);
diff --git a/security/security.c b/security/security.c
index f493db0..3308e89 100644
--- a/security/security.c
+++ b/security/security.c
@@ -1421,6 +1421,11 @@ int security_file_mprotect(struct vm_area_struct *vma, unsigned long reqprot,
return call_int_hook(file_mprotect, 0, vma, reqprot, prot);
}
+int security_check_vmflags(vm_flags_t vmflags)
+{
+ return call_int_hook(check_vmflags, 0, vmflags);
+}
+
int security_file_lock(struct file *file, unsigned int cmd)
{
return call_int_hook(file_lock, 0, file, cmd);
--
1.9.1
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