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mm: add a NO_INHERIT flag to the PR_SET_MDWE prctl 

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>
This commit is contained in:
Florent Revest 2023-08-28 17:08:57 +02:00 committed by Andrew Morton
parent 0da668333f
commit 24e41bf8a6
5 changed files with 39 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
include/linux/sched/coredump.h
View File

@ -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 */

1
include/uapi/linux/prctl.h
View File

@ -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

2
kernel/fork.c
View File

@ -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;

32
kernel/sys.c
View File

@ -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)

1
tools/include/uapi/linux/prctl.h
View File

@ -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