mm: add a NO_INHERIT flag to the PR_SET_MDWE prctl

[ Upstream commit 24e41bf8a6b424c76c5902fb999e9eca61bdf83d ]

This extends the current PR_SET_MDWE prctl arg with a bit to indicate that
the process doesn't want MDWE protection to propagate to children.

To implement this no-inherit mode, the tag in current->mm->flags must be
absent from MMF_INIT_MASK.  This means that the encoding for "MDWE but
without inherit" is different in the prctl than in the mm flags.  This
leads to a bit of bit-mangling in the prctl implementation.

Link: https://lkml.kernel.org/r/20230828150858.393570-6-revest@chromium.org
Signed-off-by: Florent Revest <revest@chromium.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Alexey Izbyshev <izbyshev@ispras.ru>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Ayush Jain <ayush.jain3@amd.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Joey Gouly <joey.gouly@arm.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Szabolcs Nagy <Szabolcs.Nagy@arm.com>
Cc: Topi Miettinen <toiwoton@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stable-dep-of: 793838138c15 ("prctl: Disable prctl(PR_SET_MDWE) on parisc")
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h
index 0ee96ea..1b37fa8 100644 (file)
--- a/include/linux/sched/coredump.h
+++ b/include/linux/sched/coredump.h
@@ -91,4 +91,14 @@ static inline int get_dumpable(struct mm_struct *mm)
                                 MMF_DISABLE_THP_MASK | MMF_HAS_MDWE_MASK)
 
 #define MMF_VM_MERGE_ANY       29
+#define MMF_HAS_MDWE_NO_INHERIT        30
+
+static inline unsigned long mmf_init_flags(unsigned long flags)
+{
+       if (flags & (1UL << MMF_HAS_MDWE_NO_INHERIT))
+               flags &= ~((1UL << MMF_HAS_MDWE) |
+                          (1UL << MMF_HAS_MDWE_NO_INHERIT));
+       return flags & MMF_INIT_MASK;
+}
+
 #endif /* _LINUX_SCHED_COREDUMP_H */

diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h
index 9a85c69..370ed14 100644 (file)
--- a/include/uapi/linux/prctl.h
+++ b/include/uapi/linux/prctl.h
@@ -284,6 +284,7 @@ struct prctl_mm_map {
 /* Memory deny write / execute */
 #define PR_SET_MDWE                    65
 # define PR_MDWE_REFUSE_EXEC_GAIN      (1UL << 0)
+# define PR_MDWE_NO_INHERIT            (1UL << 1)
 
 #define PR_GET_MDWE                    66
 

diff --git a/kernel/fork.c b/kernel/fork.c
index 3b6d20d..177ce74 100644 (file)
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1288,7 +1288,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
        hugetlb_count_init(mm);
 
        if (current->mm) {
-               mm->flags = current->mm->flags & MMF_INIT_MASK;
+               mm->flags = mmf_init_flags(current->mm->flags);
                mm->def_flags = current->mm->def_flags & VM_INIT_DEF_MASK;
        } else {
                mm->flags = default_dump_filter;

diff --git a/kernel/sys.c b/kernel/sys.c
index 2410e39..4a8073c 100644 (file)
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2368,19 +2368,41 @@ static int prctl_set_vma(unsigned long opt, unsigned long start,
 }
 #endif /* CONFIG_ANON_VMA_NAME */
 
+static inline unsigned long get_current_mdwe(void)
+{
+       unsigned long ret = 0;
+
+       if (test_bit(MMF_HAS_MDWE, &current->mm->flags))
+               ret |= PR_MDWE_REFUSE_EXEC_GAIN;
+       if (test_bit(MMF_HAS_MDWE_NO_INHERIT, &current->mm->flags))
+               ret |= PR_MDWE_NO_INHERIT;
+
+       return ret;
+}
+
 static inline int prctl_set_mdwe(unsigned long bits, unsigned long arg3,
                                 unsigned long arg4, unsigned long arg5)
 {
+       unsigned long current_bits;
+
        if (arg3 || arg4 || arg5)
                return -EINVAL;
 
-       if (bits & ~(PR_MDWE_REFUSE_EXEC_GAIN))
+       if (bits & ~(PR_MDWE_REFUSE_EXEC_GAIN | PR_MDWE_NO_INHERIT))
+               return -EINVAL;
+
+       /* NO_INHERIT only makes sense with REFUSE_EXEC_GAIN */
+       if (bits & PR_MDWE_NO_INHERIT && !(bits & PR_MDWE_REFUSE_EXEC_GAIN))
                return -EINVAL;
 
+       current_bits = get_current_mdwe();
+       if (current_bits && current_bits != bits)
+               return -EPERM; /* Cannot unset the flags */
+
+       if (bits & PR_MDWE_NO_INHERIT)
+               set_bit(MMF_HAS_MDWE_NO_INHERIT, &current->mm->flags);
        if (bits & PR_MDWE_REFUSE_EXEC_GAIN)
                set_bit(MMF_HAS_MDWE, &current->mm->flags);
-       else if (test_bit(MMF_HAS_MDWE, &current->mm->flags))
-               return -EPERM; /* Cannot unset the flag */
 
        return 0;
 }
@@ -2390,9 +2412,7 @@ static inline int prctl_get_mdwe(unsigned long arg2, unsigned long arg3,
 {
        if (arg2 || arg3 || arg4 || arg5)
                return -EINVAL;
-
-       return test_bit(MMF_HAS_MDWE, &current->mm->flags) ?
-               PR_MDWE_REFUSE_EXEC_GAIN : 0;
+       return get_current_mdwe();
 }
 
 static int prctl_get_auxv(void __user *addr, unsigned long len)

diff --git a/tools/include/uapi/linux/prctl.h b/tools/include/uapi/linux/prctl.h
index 9a85c69..370ed14 100644 (file)
--- a/tools/include/uapi/linux/prctl.h
+++ b/tools/include/uapi/linux/prctl.h
@@ -284,6 +284,7 @@ struct prctl_mm_map {
 /* Memory deny write / execute */
 #define PR_SET_MDWE                    65
 # define PR_MDWE_REFUSE_EXEC_GAIN      (1UL << 0)
+# define PR_MDWE_NO_INHERIT            (1UL << 1)
 
 #define PR_GET_MDWE                    66