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.
Add x86 arch implementations of arch_get_unmapped_area_vmflags/_topdown()
so future changes can allow the the guard gap of type of vma being placed
to be taken into account. This will be used for shadow stack memory.
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
---
v2:
- Remove unnecessary added extern
---
arch/x86/include/asm/pgtable_64.h | 1 +
arch/x86/kernel/sys_x86_64.c | 25 ++++++++++++++++++++-----
2 files changed, 21 insertions(+), 5 deletions(-)
diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
index a629b1b9f65a..eb09a11621ad 100644
--- a/arch/x86/include/asm/pgtable_64.h
+++ b/arch/x86/include/asm/pgtable_64.h
@@ -244,6 +244,7 @@ extern void cleanup_highmap(void);
#define HAVE_ARCH_UNMAPPED_AREA
#define HAVE_ARCH_UNMAPPED_AREA_TOPDOWN
+#define HAVE_ARCH_UNMAPPED_AREA_VMFLAGS
#define PAGE_AGP PAGE_KERNEL_NOCACHE
#define HAVE_PAGE_AGP 1
diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
index 6e5d4fa5fc42..95cb9efc47fb 100644
--- a/arch/x86/kernel/sys_x86_64.c
+++ b/arch/x86/kernel/sys_x86_64.c
@@ -120,8 +120,8 @@ static void find_start_end(unsigned long addr, unsigned long flags,
}
unsigned long
-arch_get_unmapped_area(struct file *filp, unsigned long addr,
- unsigned long len, unsigned long pgoff, unsigned long flags)
+arch_get_unmapped_area_vmflags(struct file *filp, unsigned long addr, unsigned long len,
+ unsigned long pgoff, unsigned long flags, vm_flags_t vm_flags)
{
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
@@ -158,9 +158,9 @@ arch_get_unmapped_area(struct file *filp, unsigned long addr,
}
unsigned long
-arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
- const unsigned long len, const unsigned long pgoff,
- const unsigned long flags)
+arch_get_unmapped_area_topdown_vmflags(struct file *filp, unsigned long addr0,
+ unsigned long len, unsigned long pgoff,
+ unsigned long flags, vm_flags_t vm_flags)
{
struct vm_area_struct *vma;
struct mm_struct *mm = current->mm;
@@ -230,3 +230,18 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
*/
return arch_get_unmapped_area(filp, addr0, len, pgoff, flags);
}
+
+unsigned long
+arch_get_unmapped_area(struct file *filp, unsigned long addr,
+ unsigned long len, unsigned long pgoff, unsigned long flags)
+{
+ return arch_get_unmapped_area_vmflags(filp, addr, len, pgoff, flags, 0);
+}
+
+unsigned long
+arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr,
+ const unsigned long len, const unsigned long pgoff,
+ const unsigned long flags)
+{
+ return arch_get_unmapped_area_topdown_vmflags(filp, addr, len, pgoff, flags, 0);
+}
--
2.34.1
