From: Muhammad Usama Anjum <usama.anjum@collabora.com>
To: jeffxu@chromium.org, akpm@linux-foundation.org,
keescook@chromium.org, jannh@google.com, sroettger@google.com,
willy@infradead.org, gregkh@linuxfoundation.org,
torvalds@linux-foundation.org
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>,
jeffxu@google.com, jorgelo@chromium.org, groeck@chromium.org,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
linux-mm@kvack.org, surenb@google.com, alex.sierra@amd.com,
apopple@nvidia.com, aneesh.kumar@linux.ibm.com,
axelrasmussen@google.com, ben@decadent.org.uk,
catalin.marinas@arm.com, david@redhat.com, dwmw@amazon.co.uk,
ying.huang@intel.com, hughd@google.com, joey.gouly@arm.com,
corbet@lwn.net, wangkefeng.wang@huawei.com,
Liam.Howlett@oracle.com, lstoakes@gmail.com,
mawupeng1@huawei.com, linmiaohe@huawei.com, namit@vmware.com,
peterx@redhat.com, peterz@infradead.org, ryan.roberts@arm.com,
shr@devkernel.io, vbabka@suse.cz, xiujianfeng@huawei.com,
yu.ma@intel.com, zhangpeng362@huawei.com, dave.hansen@intel.com,
luto@kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [RFC PATCH v2 6/8] mseal: Check seal flag for mremap(2)
Date: Fri, 20 Oct 2023 18:56:07 +0500 [thread overview]
Message-ID: <38f132b8-4fd2-40e2-b24e-62164a0ee4e6@collabora.com> (raw)
In-Reply-To: <20231017090815.1067790-7-jeffxu@chromium.org>
On 10/17/23 2:08 PM, jeffxu@chromium.org wrote:
> From: Jeff Xu <jeffxu@google.com>
>
> mremap(2) can shrink/expand a VMA, or move a VMA to a fixed
> address and overwriting or existing VMA. Sealing will
> prevent unintended mremap(2) call.
>
> What this patch does:
> When a mremap(2) is invoked, if one of its VMAs has MM_SEAL_MREMAP
> set from previous mseal(2) call, this mremap(2) will fail, without
> any VMA modified.
>
> This patch is based on following:
> 1. At syscall entry point: SYSCALL_DEFINE5(mremap,...)
> There are two cases:
Maybe we can reduce the code duplication by bringing the check if memory is
sealed before call to mremap_to().
> a. going into mremap_to().
> b. not going into mremap_to().
>
> 2. For mremap_to() case.
> Since mremap_to() is called only from SYSCALL_DEFINE5(mremap,..),
> omit changing signature of mremap_to(), i.e. not passing
> checkSeals flag.
> In mremap_to(), it calls can_modify_mm() for src address and
> dst address (when MREMAP_FIXED is used), before any update is
> made to the VMAs.
>
> 3. For non mremap_to() case.
> It is still part of SYSCALL_DEFINE5(mremap,...).
> It calls can_modify_mm() to check sealing in the src address,
> before any update is made to src VMAs.
> Check for dest address is not needed, because dest memory is
> allocated in current mremap(2) call.
>
> Signed-off-by: Jeff Xu <jeffxu@google.com>
> ---
> mm/mremap.c | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/mm/mremap.c b/mm/mremap.c
> index ac363937f8c4..691fc32d37e4 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -836,7 +836,27 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
> if ((mm->map_count + 2) >= sysctl_max_map_count - 3)
> return -ENOMEM;
>
> + /*
> + * Check src address for sealing.
> + *
> + * Note: mremap_to() currently called from one place:
> + * SYSCALL_DEFINE4(pkey_mprotect, ...)
> + * and not in any other places.
> + * Therefore, omit changing the signature of mremap_to()
> + * Otherwise, we might need to add checkSeals and pass it
> + * from all callers of mremap_to().
> + */
> + if (!can_modify_mm(mm, addr, addr + old_len, MM_SEAL_MREMAP))
> + return -EACCES;
> +
> if (flags & MREMAP_FIXED) {
> + /*
> + * Check dest address for sealing.
> + */
> + if (!can_modify_mm(mm, new_addr, new_addr + new_len,
> + MM_SEAL_MREMAP))
> + return -EACCES;
> +
Move these two checks to just before call to mremap_to() in sys_mremap() or
even earlier. Or even better move the first condition before mremap_to()
and second condition can be checked before call to mremap_to().
> ret = do_munmap(mm, new_addr, new_len, uf_unmap_early);
> if (ret)
> goto out;
> @@ -995,6 +1015,11 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
> goto out;
> }
>
> + if (!can_modify_mm(mm, addr, addr + old_len, MM_SEAL_MREMAP)) {
> + ret = -EACCES;
> + goto out;
> + }
> +
> /*
> * Always allow a shrinking remap: that just unmaps
> * the unnecessary pages..
--
BR,
Muhammad Usama Anjum
next prev parent reply other threads:[~2023-10-20 13:56 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-17 9:08 [RFC PATCH v2 0/8] Introduce mseal() syscall jeffxu
2023-10-17 9:08 ` [RFC PATCH v2 1/8] mseal: Add mseal(2) syscall jeffxu
2023-10-17 15:45 ` Randy Dunlap
2023-10-17 9:08 ` [RFC PATCH v2 2/8] mseal: Wire up mseal syscall jeffxu
2023-10-17 9:08 ` [RFC PATCH v2 3/8] mseal: add can_modify_mm and can_modify_vma jeffxu
2023-10-17 9:08 ` [RFC PATCH v2 4/8] mseal: Check seal flag for mprotect(2) jeffxu
2023-10-17 9:08 ` [RFC PATCH v2 5/8] mseal: Check seal flag for munmap(2) jeffxu
2023-10-17 16:54 ` Linus Torvalds
2023-10-18 15:08 ` Jeff Xu
2023-10-18 17:14 ` Jeff Xu
2023-10-18 18:27 ` Linus Torvalds
2023-10-18 19:07 ` Jeff Xu
2023-10-17 9:08 ` [RFC PATCH v2 6/8] mseal: Check seal flag for mremap(2) jeffxu
2023-10-20 13:56 ` Muhammad Usama Anjum [this message]
2023-10-17 9:08 ` [RFC PATCH v2 7/8] mseal:Check seal flag for mmap(2) jeffxu
2023-10-17 17:04 ` Linus Torvalds
2023-10-17 17:43 ` Linus Torvalds
2023-10-18 7:01 ` Jeff Xu
2023-10-19 7:27 ` Stephen Röttger
2023-10-17 9:08 ` [RFC PATCH v2 8/8] selftest mm/mseal mprotect/munmap/mremap/mmap jeffxu
2023-10-20 14:24 ` Muhammad Usama Anjum
2023-10-20 15:23 ` Peter Zijlstra
2023-10-20 16:33 ` Muhammad Usama Anjum
2023-10-19 9:19 ` [RFC PATCH v2 0/8] Introduce mseal() syscall David Laight
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