include/linux/mm.h | 2 ++ include/linux/security.h | 8 +++---- ipc/shm.c | 2 +- mm/mmap.c | 42 ++++++++++++++++++++++------------ mm/nommu.c | 49 +++++++++++++++++++++++++++++++--------- mm/util.c | 2 +- security/security.c | 41 ++++----------------------------- 7 files changed, 78 insertions(+), 68 deletions(-)
This patch moves the check of READ_IMPLIES_EXEC out of do_mmap(), and
calls the LSM hooks at the same time. Below is the reason.
Some logic may call do_mmap() which adding PROT_EXEC internally when the
user controlled READ_IMPLIES_EXEC flag is set, without being aware of the
harm this poses to LSM.
For example, CVE-2016-10044[1] was reported many years ago, but the
remap_file_pages() can still bypass the W^X policy enforced by SELinux[2]
for a long time.
Adding checks is easy(and has been done in all required call sites for
the current version), but there may have more calls to do_mmap() in the
future. And moving the security check in do_mmap() will let it in the
mmap_write_lock, which slows down the performance and even have deadlocks
if someone depends on it.
Moving the check of READ_IMPLIES_EXEC out of do_mmap() can keep the LSM
hook is called out of the mmap_write_lock, and avoid repeated logic for
whether READ_IMPLIES_EXEC should add PROT_EXEC for the mapping or not(In
current, the !MMU case won't implies exec if file's mmap_capabilities is
not exist, but the security check logic is different). And all known cases
that call do_mmap() become secure and anyone who want to apply the
READ_IMPLIES_EXEC logic will call the LSM hook correctly.
Some minor behavioral changes to call sites to do_mmap() and why they
should clearly be fine:
mm/util.c and ipc/shm.c: the common case, no changes in behavior.
fs/aio.c: have ensured never have PROT_EXEC in the fix of CVE-2016-10044,
so no changes in behavior.
arch/x86/kernel/shstk.c: must not want to PROT_EXEC in any case.
since shadow stack is a stack only store return addresses,
execute it is never required.
mm/mmap.c: in the history, remap_file_pages won't care about the
READ_IMPLIES_EXEC. this side effect is introduced in the emulation
version after the deprecated mark exists. The patch only remove the
side effect introduced.
Link: https://project-zero.issues.chromium.org/issues/42452389 [1]
Link: https://lore.kernel.org/all/20240919080905.4506-2-paul@paul-moore.com/ [2]
Signed-off-by: Shu Han <ebpqwerty472123@gmail.com>
---
V2: Add RFC tag as lorenzo.stoakes@oracle.com suggested, and refine the
comment in patch.
V1: https://lore.kernel.org/all/20240925063034.169-1-ebpqwerty472123@gmail.com/
Alternatives:
1. mm: move security_mmap_file() back into do_mmap()
https://lore.kernel.org/all/20240925115701.73-1-ebpqwerty472123@gmail.com/
2. Add sufficient comments for do_mmap()
---
include/linux/mm.h | 2 ++
include/linux/security.h | 8 +++----
ipc/shm.c | 2 +-
mm/mmap.c | 42 ++++++++++++++++++++++------------
mm/nommu.c | 49 +++++++++++++++++++++++++++++++---------
mm/util.c | 2 +-
security/security.c | 41 ++++-----------------------------
7 files changed, 78 insertions(+), 68 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index c4b238a20b76..83f334590b06 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3392,6 +3392,8 @@ get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
extern unsigned long mmap_region(struct file *file, unsigned long addr,
unsigned long len, vm_flags_t vm_flags, unsigned long pgoff,
struct list_head *uf);
+extern int mmap_check_prot(struct file *file, unsigned long *prot,
+ unsigned long flags);
extern unsigned long do_mmap(struct file *file, unsigned long addr,
unsigned long len, unsigned long prot, unsigned long flags,
vm_flags_t vm_flags, unsigned long pgoff, unsigned long *populate,
diff --git a/include/linux/security.h b/include/linux/security.h
index c37c32ebbdcd..e061bc9a0331 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -423,8 +423,8 @@ void security_file_free(struct file *file);
int security_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
int security_file_ioctl_compat(struct file *file, unsigned int cmd,
unsigned long arg);
-int security_mmap_file(struct file *file, unsigned long prot,
- unsigned long flags);
+int security_mmap_file(struct file *file, unsigned long reqprot,
+ unsigned long prot, unsigned long flags);
int security_mmap_addr(unsigned long addr);
int security_file_mprotect(struct vm_area_struct *vma, unsigned long reqprot,
unsigned long prot);
@@ -1077,8 +1077,8 @@ static inline int security_file_ioctl_compat(struct file *file,
return 0;
}
-static inline int security_mmap_file(struct file *file, unsigned long prot,
- unsigned long flags)
+static inline int security_mmap_file(struct file *file, unsigned long reqprot,
+ unsigned long prot, unsigned long flags)
{
return 0;
}
diff --git a/ipc/shm.c b/ipc/shm.c
index 3e3071252dac..f1095ee3796d 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -1636,7 +1636,7 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg,
sfd->vm_ops = NULL;
file->private_data = sfd;
- err = security_mmap_file(file, prot, flags);
+ err = mmap_check_prot(file, &prot, flags);
if (err)
goto out_fput;
diff --git a/mm/mmap.c b/mm/mmap.c
index 18fddcce03b8..b8992ee202fe 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1249,8 +1249,36 @@ static inline bool file_mmap_ok(struct file *file, struct inode *inode,
return true;
}
+int mmap_check_prot(struct file *file, unsigned long *prot,
+ unsigned long flags)
+{
+ unsigned long req_prot = *prot;
+ unsigned long new_prot = req_prot;
+ int err;
+
+ /*
+ * Does the application expect PROT_READ to imply PROT_EXEC?
+ *
+ * (the exception is when the underlying filesystem is noexec
+ * mounted, in which case we don't add PROT_EXEC.)
+ */
+ if (((req_prot & (PROT_READ | PROT_EXEC)) == PROT_READ) &&
+ (current->personality & READ_IMPLIES_EXEC) &&
+ !(file && path_noexec(&file->f_path)))
+ new_prot |= PROT_EXEC;
+
+ err = security_mmap_file(file, req_prot, new_prot, flags);
+ if (err)
+ return err;
+
+ *prot = new_prot;
+ return 0;
+}
+
/*
* The caller must write-lock current->mm->mmap_lock.
+ * The caller must ensure security check is not needed or
+ * call to mmap_check_prot before.
*/
unsigned long do_mmap(struct file *file, unsigned long addr,
unsigned long len, unsigned long prot,
@@ -1266,16 +1294,6 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
if (!len)
return -EINVAL;
- /*
- * Does the application expect PROT_READ to imply PROT_EXEC?
- *
- * (the exception is when the underlying filesystem is noexec
- * mounted, in which case we don't add PROT_EXEC.)
- */
- if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
- if (!(file && path_noexec(&file->f_path)))
- prot |= PROT_EXEC;
-
/* force arch specific MAP_FIXED handling in get_unmapped_area */
if (flags & MAP_FIXED_NOREPLACE)
flags |= MAP_FIXED;
@@ -3198,12 +3216,8 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
flags |= MAP_LOCKED;
file = get_file(vma->vm_file);
- ret = security_mmap_file(vma->vm_file, prot, flags);
- if (ret)
- goto out_fput;
ret = do_mmap(vma->vm_file, start, size,
prot, flags, 0, pgoff, &populate, NULL);
-out_fput:
fput(file);
out:
mmap_write_unlock(mm);
diff --git a/mm/nommu.c b/mm/nommu.c
index 7296e775e04e..96761add1295 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -792,12 +792,6 @@ static int validate_mmap_request(struct file *file,
if (path_noexec(&file->f_path)) {
if (prot & PROT_EXEC)
return -EPERM;
- } else if ((prot & PROT_READ) && !(prot & PROT_EXEC)) {
- /* handle implication of PROT_EXEC by PROT_READ */
- if (current->personality & READ_IMPLIES_EXEC) {
- if (capabilities & NOMMU_MAP_EXEC)
- prot |= PROT_EXEC;
- }
} else if ((prot & PROT_READ) &&
(prot & PROT_EXEC) &&
!(capabilities & NOMMU_MAP_EXEC)
@@ -810,11 +804,6 @@ static int validate_mmap_request(struct file *file,
* privately mapped
*/
capabilities = NOMMU_MAP_COPY;
-
- /* handle PROT_EXEC implication by PROT_READ */
- if ((prot & PROT_READ) &&
- (current->personality & READ_IMPLIES_EXEC))
- prot |= PROT_EXEC;
}
/* allow the security API to have its say */
@@ -992,6 +981,44 @@ static int do_mmap_private(struct vm_area_struct *vma,
return -ENOMEM;
}
+int mmap_check_prot(struct file *file, unsigned long *prot,
+ unsigned long flags)
+{
+ unsigned long req_prot = *prot;
+ unsigned long new_prot = req_prot;
+ int err;
+
+ /*
+ * Does the application expect PROT_READ to imply PROT_EXEC?
+ *
+ * (the exception is when the underlying filesystem is noexec
+ * mounted or the file does not have NOMMU_MAP_EXEC
+ * (== VM_MAYEXEC), in which case we don't add PROT_EXEC.)
+ */
+ if ((req_prot & (PROT_READ | PROT_EXEC)) != PROT_READ)
+ goto check;
+ if (!(current->personality & READ_IMPLIES_EXEC))
+ goto check;
+ if (!file) {
+ new_prot |= PROT_EXEC;
+ goto check;
+ }
+ if (file->f_op->mmap_capabilities) {
+ unsigned int caps = file->f_op->mmap_capabilities(file);
+
+ if (!(caps & NOMMU_MAP_EXEC))
+ goto check;
+ new_prot |= PROT_EXEC;
+ }
+check:
+ err = security_mmap_file(file, req_prot, new_prot, flags);
+ if (err)
+ return err;
+
+ *prot = new_prot;
+ return 0;
+}
+
/*
* handle mapping creation for uClinux
*/
diff --git a/mm/util.c b/mm/util.c
index bd283e2132e0..2eb4d6037610 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -581,7 +581,7 @@ unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr,
unsigned long populate;
LIST_HEAD(uf);
- ret = security_mmap_file(file, prot, flag);
+ ret = mmap_check_prot(file, &prot, flag);
if (!ret) {
if (mmap_write_lock_killable(mm))
return -EINTR;
diff --git a/security/security.c b/security/security.c
index 4564a0a1e4ef..25556629f588 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2927,42 +2927,10 @@ int security_file_ioctl_compat(struct file *file, unsigned int cmd,
}
EXPORT_SYMBOL_GPL(security_file_ioctl_compat);
-static inline unsigned long mmap_prot(struct file *file, unsigned long prot)
-{
- /*
- * Does we have PROT_READ and does the application expect
- * it to imply PROT_EXEC? If not, nothing to talk about...
- */
- if ((prot & (PROT_READ | PROT_EXEC)) != PROT_READ)
- return prot;
- if (!(current->personality & READ_IMPLIES_EXEC))
- return prot;
- /*
- * if that's an anonymous mapping, let it.
- */
- if (!file)
- return prot | PROT_EXEC;
- /*
- * ditto if it's not on noexec mount, except that on !MMU we need
- * NOMMU_MAP_EXEC (== VM_MAYEXEC) in this case
- */
- if (!path_noexec(&file->f_path)) {
-#ifndef CONFIG_MMU
- if (file->f_op->mmap_capabilities) {
- unsigned caps = file->f_op->mmap_capabilities(file);
- if (!(caps & NOMMU_MAP_EXEC))
- return prot;
- }
-#endif
- return prot | PROT_EXEC;
- }
- /* anything on noexec mount won't get PROT_EXEC */
- return prot;
-}
-
/**
* security_mmap_file() - Check if mmap'ing a file is allowed
* @file: file
+ * @reqprot: protection requested by user
* @prot: protection applied by the kernel
* @flags: flags
*
@@ -2971,11 +2939,10 @@ static inline unsigned long mmap_prot(struct file *file, unsigned long prot)
*
* Return: Returns 0 if permission is granted.
*/
-int security_mmap_file(struct file *file, unsigned long prot,
- unsigned long flags)
+int security_mmap_file(struct file *file, unsigned long reqprot,
+ unsigned long prot, unsigned long flags)
{
- return call_int_hook(mmap_file, file, prot, mmap_prot(file, prot),
- flags);
+ return call_int_hook(mmap_file, file, reqprot, prot, flags);
}
/**
base-commit: f89722faa31466ff41aed21bdeb9cf34c2312858
--
2.34.1© 2016 - 2024 Red Hat, Inc.