The patch titled
Subject: mm: use get_unmapped_area_vmflags()
has been added to the -mm mm-unstable branch. Its filename is
mm-use-get_unmapped_area_vmflags.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-use-get_unmapped_area_vmflags.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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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
Subject: mm: use get_unmapped_area_vmflags()
Date: Mon, 25 Mar 2024 19:16:47 -0700
When memory is being placed, mmap() will take care to respect the guard
gaps of certain types of memory (VM_SHADOWSTACK, VM_GROWSUP and
VM_GROWSDOWN). In order to ensure guard gaps between mappings, mmap()
needs to consider two things:
1. That the new mapping isn't placed in an any existing mappings guard
gaps.
2. That the new mapping isn't placed such that any existing mappings
are not in *its* guard gaps.
The long standing behavior of mmap() is to ensure 1, but not take any care
around 2. So for example, if there is a PAGE_SIZE free area, and a mmap()
with a PAGE_SIZE size, and a type that has a guard gap is being placed,
mmap() may place the shadow stack in the PAGE_SIZE free area. Then the
mapping that is supposed to have a guard gap will not have a gap to the
adjacent VMA.
Use mm_get_unmapped_area_vmflags() in the do_mmap() so future changes can
cause shadow stack mappings to be placed with a guard gap. Also use the
THP variant that takes vm_flags, such that THP shadow stack can get the
same treatment. Adjust the vm_flags calculation to happen earlier so that
the vm_flags can be passed into __get_unmapped_area().
Link: https://lkml.kernel.org/r/20240326021656.202649-6-rick.p.edgecombe@xxxxxxxxx
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
Reviewed-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxx>
Cc: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Deepak Gupta <debug@xxxxxxxxxxxx>
Cc: Guo Ren <guoren@xxxxxxxxxx>
Cc: Helge Deller <deller@xxxxxx>
Cc: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "James E.J. Bottomley" <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: Mark Brown <broonie@xxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 11 ++++++++++-
mm/mmap.c | 32 ++++++++++++++++----------------
2 files changed, 26 insertions(+), 17 deletions(-)
--- a/include/linux/mm.h~mm-use-get_unmapped_area_vmflags
+++ a/include/linux/mm.h
@@ -3412,7 +3412,16 @@ extern int install_special_mapping(struc
unsigned long randomize_stack_top(unsigned long stack_top);
unsigned long randomize_page(unsigned long start, unsigned long range);
-extern unsigned long get_unmapped_area(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
+unsigned long
+__get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
+ unsigned long pgoff, unsigned long flags, vm_flags_t vm_flags);
+
+static inline unsigned long
+get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
+ unsigned long pgoff, unsigned long flags)
+{
+ return __get_unmapped_area(file, addr, len, pgoff, flags, 0);
+}
extern unsigned long mmap_region(struct file *file, unsigned long addr,
unsigned long len, vm_flags_t vm_flags, unsigned long pgoff,
--- a/mm/mmap.c~mm-use-get_unmapped_area_vmflags
+++ a/mm/mmap.c
@@ -1255,18 +1255,6 @@ unsigned long do_mmap(struct file *file,
if (mm->map_count > sysctl_max_map_count)
return -ENOMEM;
- /* Obtain the address to map to. we verify (or select) it and ensure
- * that it represents a valid section of the address space.
- */
- addr = get_unmapped_area(file, addr, len, pgoff, flags);
- if (IS_ERR_VALUE(addr))
- return addr;
-
- if (flags & MAP_FIXED_NOREPLACE) {
- if (find_vma_intersection(mm, addr, addr + len))
- return -EEXIST;
- }
-
if (prot == PROT_EXEC) {
pkey = execute_only_pkey(mm);
if (pkey < 0)
@@ -1280,6 +1268,18 @@ unsigned long do_mmap(struct file *file,
vm_flags |= calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
+ /* Obtain the address to map to. we verify (or select) it and ensure
+ * that it represents a valid section of the address space.
+ */
+ addr = __get_unmapped_area(file, addr, len, pgoff, flags, vm_flags);
+ if (IS_ERR_VALUE(addr))
+ return addr;
+
+ if (flags & MAP_FIXED_NOREPLACE) {
+ if (find_vma_intersection(mm, addr, addr + len))
+ return -EEXIST;
+ }
+
if (flags & MAP_LOCKED)
if (!can_do_mlock())
return -EPERM;
@@ -1836,8 +1836,8 @@ unsigned long mm_get_unmapped_area_vmfla
}
unsigned long
-get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
- unsigned long pgoff, unsigned long flags)
+__get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
+ unsigned long pgoff, unsigned long flags, vm_flags_t vm_flags)
{
unsigned long (*get_area)(struct file *, unsigned long,
unsigned long, unsigned long, unsigned long)
@@ -1872,8 +1872,8 @@ get_unmapped_area(struct file *file, uns
if (get_area)
addr = get_area(file, addr, len, pgoff, flags);
else
- addr = mm_get_unmapped_area(current->mm, file, addr, len,
- pgoff, flags);
+ addr = mm_get_unmapped_area_vmflags(current->mm, file, addr, len,
+ pgoff, flags, vm_flags);
if (IS_ERR_VALUE(addr))
return addr;
_
Patches currently in -mm which might be from rick.p.edgecombe@xxxxxxxxx are
proc-refactor-pde_get_unmapped_area-as-prep.patch
mm-switch-mm-get_unmapped_area-to-a-flag.patch
mm-introduce-arch_get_unmapped_area_vmflags.patch
mm-remove-export-for-get_unmapped_area.patch
mm-use-get_unmapped_area_vmflags.patch
thp-add-thp_get_unmapped_area_vmflags.patch
csky-use-initializer-for-struct-vm_unmapped_area_info.patch
parisc-use-initializer-for-struct-vm_unmapped_area_info.patch
powerpc-use-initializer-for-struct-vm_unmapped_area_info.patch
treewide-use-initializer-for-struct-vm_unmapped_area_info.patch
mm-take-placement-mappings-gap-into-account.patch
x86-mm-implement-have_arch_unmapped_area_vmflags.patch
x86-mm-care-about-shadow-stack-guard-gap-during-placement.patch
selftests-x86-add-placement-guard-gap-test-for-shstk.patch
