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[PATCH v4 02/12] mm/memfd: Introduce MFD_INACCESSIBLE flag
From: |
Chao Peng |
Subject: |
[PATCH v4 02/12] mm/memfd: Introduce MFD_INACCESSIBLE flag |
Date: |
Tue, 18 Jan 2022 21:21:11 +0800 |
Introduce a new memfd_create() flag indicating the content of the
created memfd is inaccessible from userspace. It does this by force
setting F_SEAL_INACCESSIBLE seal when the file is created. It also set
F_SEAL_SEAL to prevent future sealing, which means, it can not coexist
with MFD_ALLOW_SEALING.
The pages backed by such memfd will be used as guest private memory in
confidential computing environments such as Intel TDX/AMD SEV. Since
page migration/swapping is not yet supported for such usages so these
pages are currently marked as UNMOVABLE and UNEVICTABLE which makes
them behave like long-term pinned pages.
Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
---
include/uapi/linux/memfd.h | 1 +
mm/memfd.c | 20 +++++++++++++++++++-
2 files changed, 20 insertions(+), 1 deletion(-)
diff --git a/include/uapi/linux/memfd.h b/include/uapi/linux/memfd.h
index 7a8a26751c23..48750474b904 100644
--- a/include/uapi/linux/memfd.h
+++ b/include/uapi/linux/memfd.h
@@ -8,6 +8,7 @@
#define MFD_CLOEXEC 0x0001U
#define MFD_ALLOW_SEALING 0x0002U
#define MFD_HUGETLB 0x0004U
+#define MFD_INACCESSIBLE 0x0008U
/*
* Huge page size encoding when MFD_HUGETLB is specified, and a huge page
diff --git a/mm/memfd.c b/mm/memfd.c
index 9f80f162791a..26998d96dc11 100644
--- a/mm/memfd.c
+++ b/mm/memfd.c
@@ -245,16 +245,19 @@ long memfd_fcntl(struct file *file, unsigned int cmd,
unsigned long arg)
#define MFD_NAME_PREFIX_LEN (sizeof(MFD_NAME_PREFIX) - 1)
#define MFD_NAME_MAX_LEN (NAME_MAX - MFD_NAME_PREFIX_LEN)
-#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB)
+#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB | \
+ MFD_INACCESSIBLE)
SYSCALL_DEFINE2(memfd_create,
const char __user *, uname,
unsigned int, flags)
{
+ struct address_space *mapping;
unsigned int *file_seals;
struct file *file;
int fd, error;
char *name;
+ gfp_t gfp;
long len;
if (!(flags & MFD_HUGETLB)) {
@@ -267,6 +270,10 @@ SYSCALL_DEFINE2(memfd_create,
return -EINVAL;
}
+ /* Disallow sealing when MFD_INACCESSIBLE is set. */
+ if (flags & MFD_INACCESSIBLE && flags & MFD_ALLOW_SEALING)
+ return -EINVAL;
+
/* length includes terminating zero */
len = strnlen_user(uname, MFD_NAME_MAX_LEN + 1);
if (len <= 0)
@@ -315,6 +322,17 @@ SYSCALL_DEFINE2(memfd_create,
*file_seals &= ~F_SEAL_SEAL;
}
+ if (flags & MFD_INACCESSIBLE) {
+ mapping = file_inode(file)->i_mapping;
+ gfp = mapping_gfp_mask(mapping);
+ gfp &= ~__GFP_MOVABLE;
+ mapping_set_gfp_mask(mapping, gfp);
+ mapping_set_unevictable(mapping);
+
+ file_seals = memfd_file_seals_ptr(file);
+ *file_seals &= F_SEAL_SEAL | F_SEAL_INACCESSIBLE;
+ }
+
fd_install(fd, file);
kfree(name);
return fd;
--
2.17.1
- [PATCH v4 00/12] KVM: mm: fd-based approach for supporting KVM guest private memory, Chao Peng, 2022/01/18
- [PATCH v4 01/12] mm/shmem: Introduce F_SEAL_INACCESSIBLE, Chao Peng, 2022/01/18
- [PATCH v4 02/12] mm/memfd: Introduce MFD_INACCESSIBLE flag,
Chao Peng <=
- [PATCH v4 03/12] mm: Introduce memfile_notifier, Chao Peng, 2022/01/18
- [PATCH v4 04/12] mm/shmem: Support memfile_notifier, Chao Peng, 2022/01/18
- [PATCH v4 05/12] KVM: Extend the memslot to support fd-based private memory, Chao Peng, 2022/01/18
- [PATCH v4 06/12] KVM: Use kvm_userspace_memory_region_ext, Chao Peng, 2022/01/18
- [PATCH v4 07/12] KVM: Add KVM_EXIT_MEMORY_ERROR exit, Chao Peng, 2022/01/18
- [PATCH v4 08/12] KVM: Use memfile_pfn_ops to obtain pfn for private pages, Chao Peng, 2022/01/18
- [PATCH v4 09/12] KVM: Handle page fault for private memory, Chao Peng, 2022/01/18
- [PATCH v4 10/12] KVM: Register private memslot to memory backing store, Chao Peng, 2022/01/18