From: Rick Edgecombe <rick.p.edgecombe@intel.com>
To: Liam.Howlett@oracle.com, akpm@linux-foundation.org,
debug@rivosinc.com, broonie@kernel.org,
kirill.shutemov@linux.intel.com, keescook@chromium.org,
tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
dave.hansen@linux.intel.com, x86@kernel.org, luto@kernel.org,
peterz@infradead.org, hpa@zytor.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Cc: rick.p.edgecombe@intel.com
Subject: [PATCH v2 8/9] x86/mm: Care about shadow stack guard gap during placement
Date: Mon, 26 Feb 2024 11:09:50 -0800 [thread overview]
Message-ID: <20240226190951.3240433-9-rick.p.edgecombe@intel.com> (raw)
In-Reply-To: <20240226190951.3240433-1-rick.p.edgecombe@intel.com>
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.
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.
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
---
arch/x86/kernel/sys_x86_64.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/arch/x86/kernel/sys_x86_64.c b/arch/x86/kernel/sys_x86_64.c
index 95cb9efc47fb..f44afb3345db 100644
--- a/arch/x86/kernel/sys_x86_64.c
+++ b/arch/x86/kernel/sys_x86_64.c
@@ -119,6 +119,14 @@ 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)
@@ -150,6 +158,7 @@ arch_get_unmapped_area_vmflags(struct file *filp, unsigned long addr, unsigned l
info.high_limit = end;
info.align_mask = 0;
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();
@@ -199,6 +208,7 @@ arch_get_unmapped_area_topdown_vmflags(struct file *filp, unsigned long addr0,
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
--
2.34.1
next prev parent reply other threads:[~2024-02-26 19:10 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-26 19:09 [PATCH v2 0/9] Cover a guard gap corner case Rick Edgecombe
2024-02-26 19:09 ` [PATCH v2 1/9] mm: Switch mm->get_unmapped_area() to a flag Rick Edgecombe
2024-02-26 19:09 ` [PATCH v2 2/9] mm: Introduce arch_get_unmapped_area_vmflags() Rick Edgecombe
2024-02-26 19:09 ` [PATCH v2 3/9] mm: Use get_unmapped_area_vmflags() Rick Edgecombe
2024-02-26 19:09 ` [PATCH v2 4/9] thp: Add thp_get_unmapped_area_vmflags() Rick Edgecombe
2024-02-26 19:09 ` [PATCH v2 5/9] mm: Initialize struct vm_unmapped_area_info Rick Edgecombe
2024-02-27 7:02 ` Christophe Leroy
2024-02-27 15:00 ` Edgecombe, Rick P
2024-02-27 18:07 ` Kees Cook
2024-02-27 18:16 ` Christophe Leroy
2024-02-27 20:25 ` Edgecombe, Rick P
2024-02-28 13:22 ` Christophe Leroy
2024-02-28 17:01 ` Edgecombe, Rick P
2024-02-28 23:10 ` Christophe Leroy
2024-02-28 17:21 ` Kees Cook
2024-03-02 0:47 ` Edgecombe, Rick P
2024-03-02 1:51 ` Kees Cook
2024-03-04 18:00 ` Christophe Leroy
2024-03-04 18:03 ` Edgecombe, Rick P
2024-02-28 11:51 ` Kirill A. Shutemov
[not found] ` <20240302001714.674091-1-rick.p.edgecombe@intel.com>
2024-03-02 0:17 ` [RFC v2.1 12/12] hugetlbfs: Use initializer for " Rick Edgecombe
2024-02-26 19:09 ` [PATCH v2 6/9] mm: Take placement mappings gap into account Rick Edgecombe
2024-02-26 19:09 ` [PATCH v2 7/9] x86/mm: Implement HAVE_ARCH_UNMAPPED_AREA_VMFLAGS Rick Edgecombe
2024-02-26 19:09 ` Rick Edgecombe [this message]
2024-02-26 19:09 ` [PATCH v2 9/9] selftests/x86: Add placement guard gap test for shstk Rick Edgecombe
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