The patch titled
Subject: x86/mm: care about shadow stack guard gap during placement
has been added to the -mm mm-unstable branch. Its filename is
x86-mm-care-about-shadow-stack-guard-gap-during-placement.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/x86-mm-care-about-shadow-stack-guard-gap-during-placement.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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------------------------------------------------------
From: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
Subject: x86/mm: care about shadow stack guard gap during placement
Date: Mon, 25 Mar 2024 19:16:55 -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 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@xxxxxxxxx
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
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: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
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>
---
arch/x86/kernel/sys_x86_64.c | 10 ++++++++++
1 file changed, 10 insertions(+)
--- a/arch/x86/kernel/sys_x86_64.c~x86-mm-care-about-shadow-stack-guard-gap-during-placement
+++ a/arch/x86/kernel/sys_x86_64.c
@@ -112,6 +112,14 @@ static void find_start_end(unsigned long
*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 fi
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
_
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
