[RFC PATCH v2 4/8] mseal: Check seal flag for mprotect(2)

From: jeffxu@chromium.org
To: akpm@linux-foundation.org, keescook@chromium.org,
	jannh@google.com, sroettger@google.com, willy@infradead.org,
	gregkh@linuxfoundation.org, torvalds@linux-foundation.org
Cc: 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: [RFC PATCH v2 4/8] mseal: Check seal flag for mprotect(2)
Date: Tue, 17 Oct 2023 09:08:11 +0000	[thread overview]
Message-ID: <20231017090815.1067790-5-jeffxu@chromium.org> (raw)
In-Reply-To: <20231017090815.1067790-1-jeffxu@chromium.org>

From: Jeff Xu <jeffxu@google.com>

mprotect(2) changes protection of VMAs in the given address
range. Sealing will prevent unintended mprotect call.

What this patch does:
When a mprotect(2) is invoked, if one of its VMAs has MM_SEAL_MPROTECT
set from previous mseal(2) call, this mprotect(2) will fail, without
any VMA modified.

This patch is based on following:
1. do_mprotect_pkey() currently called in two places:
SYSCALL_DEFINE3(mprotect,...)
SYSCALL_DEFINE4(pkey_mprotect, ...)
and not in any other places, therefore omit changing the signature of
do_mprotect_pkey(), i.e. not passing checkSeals flag.

2. In do_mprotect_pkey(), calls can_modify_mm() before any
update is made on the VMAs.

Signed-off-by: Jeff Xu <jeffxu@google.com>
---
 mm/mprotect.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/mm/mprotect.c b/mm/mprotect.c
index 130db91d3a8c..6321c4d0aa3f 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -32,6 +32,7 @@
 #include <linux/sched/sysctl.h>
 #include <linux/userfaultfd_k.h>
 #include <linux/memory-tiers.h>
+#include <uapi/linux/mman.h>
 #include <asm/cacheflush.h>
 #include <asm/mmu_context.h>
 #include <asm/tlbflush.h>
@@ -753,6 +754,20 @@ static int do_mprotect_pkey(unsigned long start, size_t len,
 		}
 	}
 
+       /*
+	* do_mprotect_pkey() currently called from two places:
+	* SYSCALL_DEFINE3(mprotect,...)
+	* SYSCALL_DEFINE4(pkey_mprotect, ...)
+	* and not from other places.
+	* Therefore, omit changing the signature of do_mprotect_pkey().
+	* Otherwise, we might need to add checkSeals and pass it
+	* from all callers of do_mprotect_pkey().
+	*/
+	if (!can_modify_mm(current->mm, start, end, MM_SEAL_MPROTECT)) {
+		error = -EACCES;
+		goto out;
+	}
+
 	prev = vma_prev(&vmi);
 	if (start > vma->vm_start)
 		prev = vma;
-- 
2.42.0.655.g421f12c284-goog

