The patch titled
Subject: mm: add a NO_INHERIT flag to the PR_SET_MDWE prctl
has been added to the -mm mm-unstable branch. Its filename is
mm-add-a-no_inherit-flag-to-the-pr_set_mdwe-prctl.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-add-a-no_inherit-flag-to-the-pr_set_mdwe-prctl.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Florent Revest <revest@xxxxxxxxxxxx>
Subject: mm: add a NO_INHERIT flag to the PR_SET_MDWE prctl
Date: Mon, 28 Aug 2023 17:08:57 +0200
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@xxxxxxxxxxxx
Signed-off-by: Florent Revest <revest@xxxxxxxxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Alexey Izbyshev <izbyshev@xxxxxxxxx>
Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Cc: Ayush Jain <ayush.jain3@xxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Greg Thelen <gthelen@xxxxxxxxxx>
Cc: Joey Gouly <joey.gouly@xxxxxxx>
Cc: KP Singh <kpsingh@xxxxxxxxxx>
Cc: Mark Brown <broonie@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
Cc: Szabolcs Nagy <Szabolcs.Nagy@xxxxxxx>
Cc: Topi Miettinen <toiwoton@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/sched/coredump.h | 10 +++++++++
include/uapi/linux/prctl.h | 1
kernel/fork.c | 2 -
kernel/sys.c | 32 +++++++++++++++++++++++------
tools/include/uapi/linux/prctl.h | 1
5 files changed, 39 insertions(+), 7 deletions(-)
--- a/include/linux/sched/coredump.h~mm-add-a-no_inherit-flag-to-the-pr_set_mdwe-prctl
+++ a/include/linux/sched/coredump.h
@@ -91,4 +91,14 @@ static inline int get_dumpable(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 */
--- a/include/uapi/linux/prctl.h~mm-add-a-no_inherit-flag-to-the-pr_set_mdwe-prctl
+++ a/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
--- a/kernel/fork.c~mm-add-a-no_inherit-flag-to-the-pr_set_mdwe-prctl
+++ a/kernel/fork.c
@@ -1288,7 +1288,7 @@ static struct mm_struct *mm_init(struct
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;
--- a/kernel/sys.c~mm-add-a-no_inherit-flag-to-the-pr_set_mdwe-prctl
+++ a/kernel/sys.c
@@ -2368,19 +2368,41 @@ static int prctl_set_vma(unsigned long o
}
#endif /* CONFIG_ANON_VMA_NAME */
+static inline unsigned long get_current_mdwe(void)
+{
+ unsigned long ret = 0;
+
+ if (test_bit(MMF_HAS_MDWE, ¤t->mm->flags))
+ ret |= PR_MDWE_REFUSE_EXEC_GAIN;
+ if (test_bit(MMF_HAS_MDWE_NO_INHERIT, ¤t->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, ¤t->mm->flags);
if (bits & PR_MDWE_REFUSE_EXEC_GAIN)
set_bit(MMF_HAS_MDWE, ¤t->mm->flags);
- else if (test_bit(MMF_HAS_MDWE, ¤t->mm->flags))
- return -EPERM; /* Cannot unset the flag */
return 0;
}
@@ -2390,9 +2412,7 @@ static inline int prctl_get_mdwe(unsigne
{
if (arg2 || arg3 || arg4 || arg5)
return -EINVAL;
-
- return test_bit(MMF_HAS_MDWE, ¤t->mm->flags) ?
- PR_MDWE_REFUSE_EXEC_GAIN : 0;
+ return get_current_mdwe();
}
static int prctl_get_auxv(void __user *addr, unsigned long len)
--- a/tools/include/uapi/linux/prctl.h~mm-add-a-no_inherit-flag-to-the-pr_set_mdwe-prctl
+++ a/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
_
Patches currently in -mm which might be from revest@xxxxxxxxxxxx are
kselftest-vm-fix-tabs-spaces-inconsistency-in-the-mdwe-test.patch
kselftest-vm-fix-mdwes-mmap_fixed-test-case.patch
kselftest-vm-check-errnos-in-mdwe_test.patch
mm-make-pr_mdwe_refuse_exec_gain-an-unsigned-long.patch
mm-add-a-no_inherit-flag-to-the-pr_set_mdwe-prctl.patch
kselftest-vm-add-tests-for-no-inherit-memory-deny-write-execute.patch
