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x86/mm: care about shadow stack guard gap during placement

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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.

Now that the vm_flags is passed into the arch get_unmapped_area()'s, and
vm_unmapped_area() is ready to consider it, have VM_SHADOW_STACK's get
guard gap consideration for scenario 2.

Link: https://lkml.kernel.org/r/20240326021656.202649-14-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>
This commit is contained in:
Rick Edgecombe 2024-03-25 19:16:55 -07:00 committed by Andrew Morton
parent c5ecd8eb8c
commit c44357c2e7
1 changed files with 10 additions and 0 deletions
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10
arch/x86/kernel/sys_x86_64.c
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@ -112,6 +112,14 @@ static void find_start_end(unsigned long addr, unsigned long flags,
*end = task_size_64bit(addr > DEFAULT_MAP_WINDOW);
}
static inline unsigned long stack_guard_placement(vm_flags_t vm_flags)
{
if (vm_flags & VM_SHADOW_STACK)
return PAGE_SIZE;
return 0;
}
unsigned long
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)
@ -141,6 +149,7 @@ arch_get_unmapped_area_vmflags(struct file *filp, unsigned long addr, unsigned l
info.low_limit = begin;
info.high_limit = end;
info.align_offset = pgoff << PAGE_SHIFT;
info.start_gap = stack_guard_placement(vm_flags);
if (filp) {
info.align_mask = get_align_mask();
info.align_offset += get_align_bits();
@ -190,6 +199,7 @@ get_unmapped_area:
info.low_limit = PAGE_SIZE;
info.high_limit = get_mmap_base(0);
info.start_gap = stack_guard_placement(vm_flags);
/*
* If hint address is above DEFAULT_MAP_WINDOW, look for unmapped area