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Message-ID: <20231017090815.1067790-6-jeffxu@chromium.org>
Date: Tue, 17 Oct 2023 09:08:12 +0000
From: jeffxu@...omium.org
To: akpm@...ux-foundation.org, keescook@...omium.org, jannh@...gle.com,
sroettger@...gle.com, willy@...radead.org,
gregkh@...uxfoundation.org, torvalds@...ux-foundation.org
Cc: jeffxu@...gle.com, jorgelo@...omium.org, groeck@...omium.org,
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linux-hardening@...r.kernel.org
Subject: [RFC PATCH v2 5/8] mseal: Check seal flag for munmap(2)
From: Jeff Xu <jeffxu@...gle.com>
munmap(2) unmap VMAs in the given address range.
Sealing will prevent unintended munmap(2) call.
What this patch does:
When a munmap(2) is invoked, if one of its VMAs has MM_SEAL_MUNMAP
set from previous mseal(2) call, this munmap(2) will fail,
without any VMA modified.
This patch is based on following:
1. At syscall entry point: SYSCALL_DEFINE2(munmap, ...)
Pass checkSeals = MM_SEAL_MUNMAP into __vm_munmap(),
in turn, to do_vmi_munmap().
Of all the call paths that call into do_vmi_munmap(),
this is the only place where checkSeals = MM_SEAL_MUNMAP.
The rest has checkSeals = 0.
2. In do_vmi_munmap(), calls can_modify_mm() before any
update is made to VMAs.
Signed-off-by: Jeff Xu <jeffxu@...gle.com>
---
include/linux/mm.h | 2 +-
mm/mmap.c | 21 +++++++++++++--------
mm/mremap.c | 5 +++--
3 files changed, 17 insertions(+), 11 deletions(-)
diff --git a/include/linux/mm.h b/include/linux/mm.h
index b09df8501987..f2f316522f2a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3279,7 +3279,7 @@ extern unsigned long do_mmap(struct file *file, unsigned long addr,
unsigned long pgoff, unsigned long *populate, struct list_head *uf);
extern int do_vmi_munmap(struct vma_iterator *vmi, struct mm_struct *mm,
unsigned long start, size_t len, struct list_head *uf,
- bool unlock);
+ bool unlock, unsigned long checkSeals);
extern int do_munmap(struct mm_struct *, unsigned long, size_t,
struct list_head *uf);
extern int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int behavior);
diff --git a/mm/mmap.c b/mm/mmap.c
index 414ac31aa9fa..62d592f16f45 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2601,6 +2601,7 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
* @len: The length of the range to munmap
* @uf: The userfaultfd list_head
* @unlock: set to true if the user wants to drop the mmap_lock on success
+ * @checkSeals: seal type to check.
*
* This function takes a @mas that is either pointing to the previous VMA or set
* to MA_START and sets it up to remove the mapping(s). The @len will be
@@ -2611,7 +2612,7 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
*/
int do_vmi_munmap(struct vma_iterator *vmi, struct mm_struct *mm,
unsigned long start, size_t len, struct list_head *uf,
- bool unlock)
+ bool unlock, unsigned long checkSeals)
{
unsigned long end;
struct vm_area_struct *vma;
@@ -2623,6 +2624,9 @@ int do_vmi_munmap(struct vma_iterator *vmi, struct mm_struct *mm,
if (end == start)
return -EINVAL;
+ if (!can_modify_mm(mm, start, end, checkSeals))
+ return -EACCES;
+
/* arch_unmap() might do unmaps itself. */
arch_unmap(mm, start, end);
@@ -2650,7 +2654,7 @@ int do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
{
VMA_ITERATOR(vmi, mm, start);
- return do_vmi_munmap(&vmi, mm, start, len, uf, false);
+ return do_vmi_munmap(&vmi, mm, start, len, uf, false, 0);
}
unsigned long mmap_region(struct file *file, unsigned long addr,
@@ -2684,7 +2688,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
}
/* Unmap any existing mapping in the area */
- if (do_vmi_munmap(&vmi, mm, addr, len, uf, false))
+ if (do_vmi_munmap(&vmi, mm, addr, len, uf, false, 0))
return -ENOMEM;
/*
@@ -2909,7 +2913,8 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
return error;
}
-static int __vm_munmap(unsigned long start, size_t len, bool unlock)
+static int __vm_munmap(unsigned long start, size_t len, bool unlock,
+ unsigned long checkSeals)
{
int ret;
struct mm_struct *mm = current->mm;
@@ -2919,7 +2924,7 @@ static int __vm_munmap(unsigned long start, size_t len, bool unlock)
if (mmap_write_lock_killable(mm))
return -EINTR;
- ret = do_vmi_munmap(&vmi, mm, start, len, &uf, unlock);
+ ret = do_vmi_munmap(&vmi, mm, start, len, &uf, unlock, checkSeals);
if (ret || !unlock)
mmap_write_unlock(mm);
@@ -2929,14 +2934,14 @@ static int __vm_munmap(unsigned long start, size_t len, bool unlock)
int vm_munmap(unsigned long start, size_t len)
{
- return __vm_munmap(start, len, false);
+ return __vm_munmap(start, len, false, 0);
}
EXPORT_SYMBOL(vm_munmap);
SYSCALL_DEFINE2(munmap, unsigned long, addr, size_t, len)
{
addr = untagged_addr(addr);
- return __vm_munmap(addr, len, true);
+ return __vm_munmap(addr, len, true, MM_SEAL_MUNMAP);
}
@@ -3168,7 +3173,7 @@ int vm_brk_flags(unsigned long addr, unsigned long request, unsigned long flags)
if (ret)
goto limits_failed;
- ret = do_vmi_munmap(&vmi, mm, addr, len, &uf, 0);
+ ret = do_vmi_munmap(&vmi, mm, addr, len, &uf, 0, 0);
if (ret)
goto munmap_failed;
diff --git a/mm/mremap.c b/mm/mremap.c
index 056478c106ee..ac363937f8c4 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -715,7 +715,8 @@ static unsigned long move_vma(struct vm_area_struct *vma,
}
vma_iter_init(&vmi, mm, old_addr);
- if (!do_vmi_munmap(&vmi, mm, old_addr, old_len, uf_unmap, false)) {
+ if (!do_vmi_munmap(&vmi, mm, old_addr, old_len, uf_unmap, false,
+ 0)) {
/* OOM: unable to split vma, just get accounts right */
if (vm_flags & VM_ACCOUNT && !(flags & MREMAP_DONTUNMAP))
vm_acct_memory(old_len >> PAGE_SHIFT);
@@ -1009,7 +1010,7 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
}
ret = do_vmi_munmap(&vmi, mm, addr + new_len, old_len - new_len,
- &uf_unmap, true);
+ &uf_unmap, true, 0);
if (ret)
goto out;
--
2.42.0.655.g421f12c284-goog
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