From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: Liam.Howlett@oracle.com, akpm@linux-foundation.org,
debug@rivosinc.com, broonie@kernel.org, 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
Subject: Re: [RFC PATCH 5/8] mm: Take placement mappings gap into account
Date: Fri, 16 Feb 2024 15:12:39 +0200 [thread overview]
Message-ID: <3ynogxcgokc6i6xojbxzzwqectg472laes24u7jmtktlxcch5e@dfytra3ia3zc> (raw)
In-Reply-To: <20240215231332.1556787-6-rick.p.edgecombe@intel.com>
On Thu, Feb 15, 2024 at 03:13:29PM -0800, Rick Edgecombe wrote:
> 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.
>
> For MAP_GROWSDOWN/VM_GROWSDOWN and MAP_GROWSUP/VM_GROWSUP this has not
> been a problem in practice because applications place these kinds of
> mappings very early, when there is not many mappings to find a space
> between. But for shadow stacks, they may be placed throughout the lifetime
> of the application.
>
> So define a VM_UNMAPPED_START_GAP_SET flag to specify that a start_gap
> field has been set, as most vm_unmapped_area_info structs are not zeroed,
> so the added field will often contain garbage. Use
> VM_UNMAPPED_START_GAP_SET in unmapped_area/_topdown() to find a space that
> includes the guard gap for the new mapping. Take care to not interfere
> with the alignment.
>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> ---
> include/linux/mm.h | 2 ++
> mm/mmap.c | 21 ++++++++++++++-------
> 2 files changed, 16 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 9addf16dbf18..160bb6db7a16 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3393,12 +3393,14 @@ extern unsigned long __must_check vm_mmap(struct file *, unsigned long,
>
> struct vm_unmapped_area_info {
> #define VM_UNMAPPED_AREA_TOPDOWN 1
> +#define VM_UNMAPPED_START_GAP_SET 2
The flag seems to be an workaround not to clear the structure. I think
users need to be updated to clear the structure. In most cases rework code
to use C99 struct initializer would do the trick.
> unsigned long flags;
> unsigned long length;
> unsigned long low_limit;
> unsigned long high_limit;
> unsigned long align_mask;
> unsigned long align_offset;
> + unsigned long start_gap;
> };
>
> extern unsigned long vm_unmapped_area(struct vm_unmapped_area_info *info);
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 936d728ba1ca..1b6c333656f9 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1567,14 +1567,17 @@ static inline int accountable_mapping(struct file *file, vm_flags_t vm_flags)
> */
> static unsigned long unmapped_area(struct vm_unmapped_area_info *info)
> {
> - unsigned long length, gap;
> + unsigned long length, gap, start_gap = 0;
> unsigned long low_limit, high_limit;
> struct vm_area_struct *tmp;
>
> MA_STATE(mas, ¤t->mm->mm_mt, 0, 0);
>
> + if (info->flags & VM_UNMAPPED_START_GAP_SET)
> + start_gap = info->start_gap;
> +
> /* Adjust search length to account for worst case alignment overhead */
> - length = info->length + info->align_mask;
> + length = info->length + info->align_mask + start_gap;
> if (length < info->length)
> return -ENOMEM;
>
> @@ -1586,7 +1589,7 @@ static unsigned long unmapped_area(struct vm_unmapped_area_info *info)
> if (mas_empty_area(&mas, low_limit, high_limit - 1, length))
> return -ENOMEM;
>
> - gap = mas.index;
> + gap = mas.index + start_gap;
> gap += (info->align_offset - gap) & info->align_mask;
Do we care to check if alignment itself would satisfy start_gap
requirement?
> tmp = mas_next(&mas, ULONG_MAX);
> if (tmp && (tmp->vm_flags & VM_STARTGAP_FLAGS)) { /* Avoid prev check if possible */
> @@ -1619,13 +1622,17 @@ static unsigned long unmapped_area(struct vm_unmapped_area_info *info)
> */
> static unsigned long unmapped_area_topdown(struct vm_unmapped_area_info *info)
> {
> - unsigned long length, gap, gap_end;
> + unsigned long length, gap, gap_end, start_gap = 0;
> unsigned long low_limit, high_limit;
> struct vm_area_struct *tmp;
>
> MA_STATE(mas, ¤t->mm->mm_mt, 0, 0);
> +
> + if (info->flags & VM_UNMAPPED_START_GAP_SET)
> + start_gap = info->start_gap;
> +
> /* Adjust search length to account for worst case alignment overhead */
> - length = info->length + info->align_mask;
> + length = info->length + info->align_mask + start_gap;
> if (length < info->length)
> return -ENOMEM;
>
> @@ -1832,7 +1839,7 @@ unsigned long mm_get_unmapped_area_vmflags(struct mm_struct *mm, struct file *fi
>
> unsigned long
> __get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
> - unsigned long pgoff, unsigned long flags, vm_flags_t vm_flags)
> + unsigned long pgoff, unsigned long flags, vm_flags_t vm_flags)
Unrelated space change.
> {
> unsigned long (*get_area)(struct file *, unsigned long,
> unsigned long, unsigned long, unsigned long)
> @@ -1883,7 +1890,7 @@ __get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
>
> unsigned long
> get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
> - unsigned long pgoff, unsigned long flags)
> + unsigned long pgoff, unsigned long flags)
Ditto.
> {
> return __get_unmapped_area(file, addr, len, pgoff, flags, 0);
> }
> --
> 2.34.1
>
--
Kiryl Shutsemau / Kirill A. Shutemov
next prev parent reply other threads:[~2024-02-16 13:12 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-15 23:13 [RFC PATCH 0/8] Cover a guard gap corner case Rick Edgecombe
2024-02-15 23:13 ` [RFC PATCH 1/8] mm: Switch mm->get_unmapped_area() to a flag Rick Edgecombe
2024-02-16 0:30 ` Dave Hansen
2024-02-16 2:15 ` Liam R. Howlett
2024-02-16 12:30 ` Kirill A. Shutemov
2024-02-16 21:42 ` Edgecombe, Rick P
2024-02-21 7:10 ` Mike Rapoport
2024-02-21 16:59 ` Edgecombe, Rick P
2024-02-15 23:13 ` [RFC PATCH 2/8] mm: Introduce arch_get_unmapped_area_vmflags() Rick Edgecombe
2024-02-15 23:13 ` [RFC PATCH 3/8] mm: Use get_unmapped_area_vmflags() Rick Edgecombe
2024-02-16 12:56 ` Kirill A. Shutemov
2024-02-16 22:15 ` Edgecombe, Rick P
2024-02-17 12:35 ` kirill.shutemov
2024-02-15 23:13 ` [RFC PATCH 4/8] thp: Add thp_get_unmapped_area_vmflags() Rick Edgecombe
2024-02-16 12:59 ` Kirill A. Shutemov
2024-02-16 22:21 ` Edgecombe, Rick P
2024-02-17 12:57 ` kirill.shutemov
2024-02-15 23:13 ` [RFC PATCH 5/8] mm: Take placement mappings gap into account Rick Edgecombe
2024-02-16 13:12 ` Kirill A. Shutemov [this message]
2024-02-17 1:11 ` Edgecombe, Rick P
2024-02-20 16:48 ` Edgecombe, Rick P
2024-02-15 23:13 ` [RFC PATCH 6/8] x86/mm: Implement HAVE_ARCH_UNMAPPED_AREA_VMFLAGS Rick Edgecombe
2024-02-15 23:13 ` [RFC PATCH 7/8] x86/mm: Care about shadow stack guard gap during placement Rick Edgecombe
2024-02-15 23:13 ` [RFC PATCH 8/8] selftests/x86: Add placement guard gap test for shstk Rick Edgecombe
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=3ynogxcgokc6i6xojbxzzwqectg472laes24u7jmtktlxcch5e@dfytra3ia3zc \
--to=kirill.shutemov@linux.intel.com \
--cc=Liam.Howlett@oracle.com \
--cc=akpm@linux-foundation.org \
--cc=bp@alien8.de \
--cc=broonie@kernel.org \
--cc=dave.hansen@linux.intel.com \
--cc=debug@rivosinc.com \
--cc=hpa@zytor.com \
--cc=keescook@chromium.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=luto@kernel.org \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=rick.p.edgecombe@intel.com \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).