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@xxxxxxxxxxxxxx/ [2] Signed-off-by: Shu Han <ebpqwerty472123@xxxxxxxxx> --- V2: Add RFC tag as lorenzo.stoakes@xxxxxxxxxx suggested, and refine the comment in patch. V1: https://lore.kernel.org/all/20240925063034.169-1-ebpqwerty472123@xxxxxxxxx/ Alternatives: 1. mm: move security_mmap_file() back into do_mmap() https://lore.kernel.org/all/20240925115701.73-1-ebpqwerty472123@xxxxxxxxx/ 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
