Commit c5ecd8eb authored Mar 25, 2024 by Rick Edgecombe Committed by Andrew Morton Apr 25, 2024

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 longstanding 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.

Link: https://lkml.kernel.org/r/20240326021656.202649-13-rick.p.edgecombe@intel.com


Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Deepak Gupta <debug@rivosinc.com>
Cc: Guo Ren <guoren@kernel.org>
Cc: Helge Deller <deller@gmx.de>
Cc: H. Peter Anvin (Intel) <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Naveen N. Rao <naveen.n.rao@linux.ibm.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

parent 44bd7ace

arch/x86/include/asm/pgtable_64.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -245,6 +245,7 @@ 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

arch/x86/kernel/sys_x86_64.c

+20 −5

Original line number	Diff line number	Diff line
		@@ -113,8 +113,8 @@ 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;
		@@ -149,9 +149,9 @@ 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;
		@@ -220,3 +220,18 @@ 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);
		}