linux-kernel - [PATCH v3 10/12] x86/mm: Implement HAVE_ARCH_UNMAPPED_AREA

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Date: Tue, 12 Mar 2024 15:28:41 -0700
From: Rick Edgecombe <rick.p.edgecombe@...el.com>
To: Liam.Howlett@...cle.com,
	akpm@...ux-foundation.org,
	bp@...en8.de,
	broonie@...nel.org,
	dave.hansen@...ux.intel.com,
	debug@...osinc.com,
	hpa@...or.com,
	keescook@...omium.org,
	kirill.shutemov@...ux.intel.com,
	luto@...nel.org,
	mingo@...hat.com,
	peterz@...radead.org,
	tglx@...utronix.de,
	x86@...nel.org,
	christophe.leroy@...roup.eu
Cc: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	rick.p.edgecombe@...el.com
Subject: [PATCH v3 10/12] x86/mm: Implement HAVE_ARCH_UNMAPPED_AREA_VMFLAGS

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 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@...el.com>
---
v3:
 - Commit log grammar

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 24af25b1551a..13dcaf436efd 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 b3278e4f7e59..d6fbc4dd08ef 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;
@@ -156,9 +156,9 @@ 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;
@@ -227,3 +227,18 @@ 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