From: Joel Fernandes (Google) <hidden> Date: 2018-11-20 05:22:00
A better way to do F_SEAL_FUTURE_WRITE seal was discussed [1] last week
where we don't need to modify core VFS structures to get the same
behavior of the seal. This solves several side-effects pointed out by
Andy [2].
[1] https://lore.kernel.org/lkml/20181111173650.GA256781@google.com/
[2] https://lore.kernel.org/lkml/69CE06CC-E47C-4992-848A-66EB23EE6C74@amacapital.net/
Suggested-by: Andy Lutomirski <luto@kernel.org>
Fixes: 5e653c2923fd ("mm: Add an F_SEAL_FUTURE_WRITE seal to memfd")
Signed-off-by: Joel Fernandes (Google) <redacted>
---
fs/hugetlbfs/inode.c | 2 +-
mm/memfd.c | 19 -------------------
mm/shmem.c | 24 +++++++++++++++++++++---
3 files changed, 22 insertions(+), 23 deletions(-)
@@ -2121,6 +2121,23 @@ int shmem_lock(struct file *file, int lock, struct user_struct *user)staticintshmem_mmap(structfile*file,structvm_area_struct*vma){+structshmem_inode_info*info=SHMEM_I(file_inode(file));++/*+*NewPROT_READandMAP_SHAREDmmapsarenotallowedwhen"future+*write" seal active.+*/+if((vma->vm_flags&VM_SHARED)&&(vma->vm_flags&VM_WRITE)&&+(info->seals&F_SEAL_FUTURE_WRITE))+return-EPERM;++/*+*SincetheF_SEAL_FUTURE_WRITEsealsallowforaMAP_SHAREDread-only+*mapping,takecaretonotallowmprotecttorevertprotections.+*/+if(info->seals&F_SEAL_FUTURE_WRITE)+vma->vm_flags&=~(VM_MAYWRITE);+file_accessed(file);vma->vm_ops=&shmem_vm_ops;if(IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE)&&
@@ -2346,8 +2363,9 @@ shmem_write_begin(struct file *file, struct address_space *mapping,pgoff_tindex=pos>>PAGE_SHIFT;/* i_mutex is held by caller */-if(unlikely(info->seals&(F_SEAL_WRITE|F_SEAL_GROW))){-if(info->seals&F_SEAL_WRITE)+if(unlikely(info->seals&(F_SEAL_GROW|+F_SEAL_WRITE|F_SEAL_FUTURE_WRITE))){+if(info->seals&(F_SEAL_WRITE|F_SEAL_FUTURE_WRITE))return-EPERM;if((info->seals&F_SEAL_GROW)&&pos+len>inode->i_size)return-EPERM;
@@ -2610,7 +2628,7 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,DECLARE_WAIT_QUEUE_HEAD_ONSTACK(shmem_falloc_waitq);/* protected by i_mutex */-if(info->seals&F_SEAL_WRITE){+if(info->seals&(F_SEAL_WRITE|F_SEAL_FUTURE_WRITE)){error=-EPERM;gotoout;}
From: Joel Fernandes (Google) <hidden> Date: 2018-11-20 05:22:03
Modify the tests for F_SEAL_FUTURE_WRITE based on the changes
introduced in previous patch.
Also add a test to make sure the reopen issue pointed by Jann Horn [1]
is fixed.
[1] https://lore.kernel.org/lkml/CAG48ez1h=v-JYnDw81HaYJzOfrNhwYksxmc2r=cJvdQVgYM+NA@mail.gmail.com/
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Joel Fernandes (Google) <redacted>
---
tools/testing/selftests/memfd/memfd_test.c | 88 +++++++++++-----------
1 file changed, 44 insertions(+), 44 deletions(-)
@@ -710,58 +745,23 @@ static void test_seal_future_write(void)p=mfd_assert_mmap_shared(fd);mfd_assert_has_seals(fd,0);-/* Not adding grow/shrink seals makes the future write-*sealfailtogetadded-*/-mfd_fail_add_seals(fd,F_SEAL_FUTURE_WRITE);--mfd_assert_add_seals(fd,F_SEAL_GROW);-mfd_assert_has_seals(fd,F_SEAL_GROW);--/* Should still fail since shrink seal has-*notyetbeenadded-*/-mfd_fail_add_seals(fd,F_SEAL_FUTURE_WRITE);--mfd_assert_add_seals(fd,F_SEAL_SHRINK);-mfd_assert_has_seals(fd,F_SEAL_GROW|-F_SEAL_SHRINK);-/* Now should succeed, also verifies that the seal-*couldbeaddedwithanexistingwritablemmap-*/mfd_assert_add_seals(fd,F_SEAL_FUTURE_WRITE);-mfd_assert_has_seals(fd,F_SEAL_SHRINK|-F_SEAL_GROW|-F_SEAL_FUTURE_WRITE);+mfd_assert_has_seals(fd,F_SEAL_FUTURE_WRITE);/* read should pass, writes should fail */mfd_assert_read(fd);+mfd_assert_read_shared(fd);mfd_fail_write(fd);-munmap(p,mfd_def_size);-close(fd);--/* Test adding all seals (grow, shrink, future write) at once */-fd=mfd_assert_new("kern_memfd_seal_future_write2",-mfd_def_size,-MFD_CLOEXEC|MFD_ALLOW_SEALING);--p=mfd_assert_mmap_shared(fd);--mfd_assert_has_seals(fd,0);-mfd_assert_add_seals(fd,F_SEAL_SHRINK|-F_SEAL_GROW|-F_SEAL_FUTURE_WRITE);-mfd_assert_has_seals(fd,F_SEAL_SHRINK|-F_SEAL_GROW|-F_SEAL_FUTURE_WRITE);--/* read should pass, writes should fail */-mfd_assert_read(fd);-mfd_fail_write(fd);+fd2=mfd_assert_reopen_fd(fd);+/* read should pass, writes should still fail */+mfd_assert_read(fd2);+mfd_assert_read_shared(fd2);+mfd_fail_write(fd2);munmap(p,mfd_def_size);+close(fd2);close(fd);}
What tree is that commit in? Can we not just fold this in?
It is in linux-next. Could we keep both commits so we have the history?
Well, its in Andrew's mmotm, so its up to him.
Unless mmotm is more magical than I think, the commit hash in your fixed tag is already nonsense. mmotm gets rebased all the time, and is only barely a git tree.
What tree is that commit in? Can we not just fold this in?
It is in linux-next. Could we keep both commits so we have the history?
Well, its in Andrew's mmotm, so its up to him.
Unless mmotm is more magical than I think, the commit hash in your fixed
tag is already nonsense. mmotm gets rebased all the time, and is only
barely a git tree.
I wouldn't go so far to call it nonsense. It was a working patch, it just did
things differently. Your help with improving the patch is much appreciated.
I am Ok with whatever Andrew wants to do, if it is better to squash it with
the original, then I can do that and send another patch.
- Joel
From: Andy Lutomirski <luto@amacapital.net> Date: 2018-11-20 21:03:23
On Nov 20, 2018, at 1:47 PM, Joel Fernandes [off-list ref] wrote:
quoted
On Tue, Nov 20, 2018 at 01:33:18PM -0700, Andy Lutomirski wrote:
quoted
On Nov 20, 2018, at 1:07 PM, Stephen Rothwell [off-list ref] wrote:
Hi Joel,
quoted
quoted
On Tue, 20 Nov 2018 10:39:26 -0800 Joel Fernandes [off-list ref] wrote:
On Tue, Nov 20, 2018 at 07:13:17AM -0800, Andy Lutomirski wrote:
On Mon, Nov 19, 2018 at 9:21 PM Joel Fernandes (Google)
[off-list ref] wrote:
What tree is that commit in? Can we not just fold this in?
It is in linux-next. Could we keep both commits so we have the history?
Well, its in Andrew's mmotm, so its up to him.
Unless mmotm is more magical than I think, the commit hash in your fixed
tag is already nonsense. mmotm gets rebased all the time, and is only
barely a git tree.
I wouldn't go so far to call it nonsense. It was a working patch, it just did
things differently. Your help with improving the patch is much appreciated.
I’m not saying the patch is nonsense — I’m saying the *hash* may be nonsense. akpm uses a bunch of .patch files and all kinds of crazy scripts, and the mmotm.git tree is not stable at all.
I am Ok with whatever Andrew wants to do, if it is better to squash it with
the original, then I can do that and send another patch.
From experience, Andrew will food in fixups on request :)
From: Joel Fernandes <hidden> Date: 2018-11-20 21:14:08
On Tue, Nov 20, 2018 at 02:02:49PM -0700, Andy Lutomirski wrote:
quoted
On Nov 20, 2018, at 1:47 PM, Joel Fernandes [off-list ref] wrote:
quoted
On Tue, Nov 20, 2018 at 01:33:18PM -0700, Andy Lutomirski wrote:
quoted
On Nov 20, 2018, at 1:07 PM, Stephen Rothwell [off-list ref] wrote:
Hi Joel,
quoted
quoted
On Tue, 20 Nov 2018 10:39:26 -0800 Joel Fernandes [off-list ref] wrote:
On Tue, Nov 20, 2018 at 07:13:17AM -0800, Andy Lutomirski wrote:
On Mon, Nov 19, 2018 at 9:21 PM Joel Fernandes (Google)
[off-list ref] wrote:
What tree is that commit in? Can we not just fold this in?
It is in linux-next. Could we keep both commits so we have the history?
Well, its in Andrew's mmotm, so its up to him.
Unless mmotm is more magical than I think, the commit hash in your fixed
tag is already nonsense. mmotm gets rebased all the time, and is only
barely a git tree.
I wouldn't go so far to call it nonsense. It was a working patch, it just did
things differently. Your help with improving the patch is much appreciated.
I’m not saying the patch is nonsense — I’m saying the *hash* may be
nonsense. akpm uses a bunch of .patch files and all kinds of crazy scripts,
and the mmotm.git tree is not stable at all.
Oh, ok. Sorry for misunderstanding and thanks for clarification. :-)
quoted
I am Ok with whatever Andrew wants to do, if it is better to squash it with
the original, then I can do that and send another patch.
From experience, Andrew will food in fixups on request :)
Andrew, could you squash this patch into the one titled ("mm: Add an
F_SEAL_FUTURE_WRITE seal to memfd")? That one was already picked up by -next
but I imagine you might have a crazy script as Andy pointed out for exactly
these situations. ;-)
thanks,
- Joel
From: Andrew Morton <akpm@linux-foundation.org> Date: 2018-11-22 02:27:06
On Tue, 20 Nov 2018 13:13:35 -0800 Joel Fernandes [off-list ref] wrote:
quoted
quoted
I am Ok with whatever Andrew wants to do, if it is better to squash it with
the original, then I can do that and send another patch.
From experience, Andrew will food in fixups on request :)
Andrew, could you squash this patch into the one titled ("mm: Add an
F_SEAL_FUTURE_WRITE seal to memfd")?
Sure.
I could of course queue them separately but I rarely do so - I don't
think that the intermediate development states are useful in the
infinite-term, and I make them available via additional Link: tags in
the changelog footers anyway.
I think that the magnitude of these patches is such that John Stultz's
Reviewed-by is invalidated, so this series is now in the "unreviewed"
state.
So can we have a re-review please? For convenience, here's the
folded-together [1/1] patch, as it will go to Linus.
From: "Joel Fernandes (Google)" <redacted>
Subject: mm: Add an F_SEAL_FUTURE_WRITE seal to memfd
Android uses ashmem for sharing memory regions. We are looking forward to
migrating all usecases of ashmem to memfd so that we can possibly remove
the ashmem driver in the future from staging while also benefiting from
using memfd and contributing to it. Note staging drivers are also not ABI
and generally can be removed at anytime.
One of the main usecases Android has is the ability to create a region and
mmap it as writeable, then add protection against making any "future"
writes while keeping the existing already mmap'ed writeable-region active.
This allows us to implement a usecase where receivers of the shared
memory buffer can get a read-only view, while the sender continues to
write to the buffer. See CursorWindow documentation in Android for more
details:
https://developer.android.com/reference/android/database/CursorWindow
This usecase cannot be implemented with the existing F_SEAL_WRITE seal.
To support the usecase, this patch adds a new F_SEAL_FUTURE_WRITE seal
which prevents any future mmap and write syscalls from succeeding while
keeping the existing mmap active. The following program shows the seal
working in action:
#include <stdio.h>
#include <errno.h>
#include <sys/mman.h>
#include <linux/memfd.h>
#include <linux/fcntl.h>
#include <asm/unistd.h>
#include <unistd.h>
#define F_SEAL_FUTURE_WRITE 0x0010
#define REGION_SIZE (5 * 1024 * 1024)
int memfd_create_region(const char *name, size_t size)
{
int ret;
int fd = syscall(__NR_memfd_create, name, MFD_ALLOW_SEALING);
if (fd < 0) return fd;
ret = ftruncate(fd, size);
if (ret < 0) { close(fd); return ret; }
return fd;
}
int main() {
int ret, fd;
void *addr, *addr2, *addr3, *addr1;
ret = memfd_create_region("test_region", REGION_SIZE);
printf("ret=%d\n", ret);
fd = ret;
// Create map
addr = mmap(0, REGION_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
if (addr == MAP_FAILED)
printf("map 0 failed\n");
else
printf("map 0 passed\n");
if ((ret = write(fd, "test", 4)) != 4)
printf("write failed even though no future-write seal "
"(ret=%d errno =%d)\n", ret, errno);
else
printf("write passed\n");
addr1 = mmap(0, REGION_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
if (addr1 == MAP_FAILED)
perror("map 1 prot-write failed even though no seal\n");
else
printf("map 1 prot-write passed as expected\n");
ret = fcntl(fd, F_ADD_SEALS, F_SEAL_FUTURE_WRITE |
F_SEAL_GROW |
F_SEAL_SHRINK);
if (ret == -1)
printf("fcntl failed, errno: %d\n", errno);
else
printf("future-write seal now active\n");
if ((ret = write(fd, "test", 4)) != 4)
printf("write failed as expected due to future-write seal\n");
else
printf("write passed (unexpected)\n");
addr2 = mmap(0, REGION_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
if (addr2 == MAP_FAILED)
perror("map 2 prot-write failed as expected due to seal\n");
else
printf("map 2 passed\n");
addr3 = mmap(0, REGION_SIZE, PROT_READ, MAP_SHARED, fd, 0);
if (addr3 == MAP_FAILED)
perror("map 3 failed\n");
else
printf("map 3 prot-read passed as expected\n");
}
The output of running this program is as follows:
ret=3
map 0 passed
write passed
map 1 prot-write passed as expected
future-write seal now active
write failed as expected due to future-write seal
map 2 prot-write failed as expected due to seal
: Permission denied
map 3 prot-read passed as expected
[joel@joelfernandes.org: make F_SEAL_FUTURE_WRITE seal more robust]
Link: http://lkml.kernel.org/r/20181120052137.74317-1-joel@joelfernandes.org
Link: http://lkml.kernel.org/r/20181108041537.39694-1-joel@joelfernandes.org
Signed-off-by: Joel Fernandes (Google) <redacted>
Cc: John Stultz <redacted>
Cc: John Reck <redacted>
Cc: Todd Kjos <redacted>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Daniel Colascione <redacted>
Cc: J. Bruce Fields <redacted>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Khalid Aziz <redacted>
Cc: Lei Yang <redacted>
Cc: Marc-Andr Lureau <redacted>
Cc: Mike Kravetz <redacted>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Valdis Kletnieks <redacted>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
@@ -530,7 +530,7 @@ static long hugetlbfs_punch_hole(structinode_lock(inode);/* protected by i_mutex */-if(info->seals&F_SEAL_WRITE){+if(info->seals&(F_SEAL_WRITE|F_SEAL_FUTURE_WRITE)){inode_unlock(inode);return-EPERM;}---a/mm/shmem.c~mm-add-an-f_seal_future_write-seal-to-memfd+++a/mm/shmem.c
@@ -2119,6 +2119,23 @@ out_nomem:staticintshmem_mmap(structfile*file,structvm_area_struct*vma){+structshmem_inode_info*info=SHMEM_I(file_inode(file));++/*+*NewPROT_READandMAP_SHAREDmmapsarenotallowedwhen"future+*write" seal active.+*/+if((vma->vm_flags&VM_SHARED)&&(vma->vm_flags&VM_WRITE)&&+(info->seals&F_SEAL_FUTURE_WRITE))+return-EPERM;++/*+*SincetheF_SEAL_FUTURE_WRITEsealsallowforaMAP_SHAREDread-only+*mapping,takecaretonotallowmprotecttorevertprotections.+*/+if(info->seals&F_SEAL_FUTURE_WRITE)+vma->vm_flags&=~(VM_MAYWRITE);+file_accessed(file);vma->vm_ops=&shmem_vm_ops;if(IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE)&&
@@ -2344,8 +2361,9 @@ shmem_write_begin(struct file *file, strpgoff_tindex=pos>>PAGE_SHIFT;/* i_mutex is held by caller */-if(unlikely(info->seals&(F_SEAL_WRITE|F_SEAL_GROW))){-if(info->seals&F_SEAL_WRITE)+if(unlikely(info->seals&(F_SEAL_GROW|+F_SEAL_WRITE|F_SEAL_FUTURE_WRITE))){+if(info->seals&(F_SEAL_WRITE|F_SEAL_FUTURE_WRITE))return-EPERM;if((info->seals&F_SEAL_GROW)&&pos+len>inode->i_size)return-EPERM;
@@ -2608,7 +2626,7 @@ static long shmem_fallocate(struct fileDECLARE_WAIT_QUEUE_HEAD_ONSTACK(shmem_falloc_waitq);/* protected by i_mutex */-if(info->seals&F_SEAL_WRITE){+if(info->seals&(F_SEAL_WRITE|F_SEAL_FUTURE_WRITE)){error=-EPERM;gotoout;}
From: Andy Lutomirski <luto@kernel.org> Date: 2018-11-22 03:25:43
On Wed, Nov 21, 2018 at 6:27 PM Andrew Morton [off-list ref] wrote:
quoted hunk
On Tue, 20 Nov 2018 13:13:35 -0800 Joel Fernandes [off-list ref] wrote:
quoted
quoted
quoted
I am Ok with whatever Andrew wants to do, if it is better to squash it with
the original, then I can do that and send another patch.
From experience, Andrew will food in fixups on request :)
Andrew, could you squash this patch into the one titled ("mm: Add an
F_SEAL_FUTURE_WRITE seal to memfd")?
Sure.
I could of course queue them separately but I rarely do so - I don't
think that the intermediate development states are useful in the
infinite-term, and I make them available via additional Link: tags in
the changelog footers anyway.
I think that the magnitude of these patches is such that John Stultz's
Reviewed-by is invalidated, so this series is now in the "unreviewed"
state.
So can we have a re-review please? For convenience, here's the
folded-together [1/1] patch, as it will go to Linus.
From: "Joel Fernandes (Google)" <redacted>
Subject: mm: Add an F_SEAL_FUTURE_WRITE seal to memfd
Android uses ashmem for sharing memory regions. We are looking forward to
migrating all usecases of ashmem to memfd so that we can possibly remove
the ashmem driver in the future from staging while also benefiting from
using memfd and contributing to it. Note staging drivers are also not ABI
and generally can be removed at anytime.
One of the main usecases Android has is the ability to create a region and
mmap it as writeable, then add protection against making any "future"
writes while keeping the existing already mmap'ed writeable-region active.
This allows us to implement a usecase where receivers of the shared
memory buffer can get a read-only view, while the sender continues to
write to the buffer. See CursorWindow documentation in Android for more
details:
https://developer.android.com/reference/android/database/CursorWindow
This usecase cannot be implemented with the existing F_SEAL_WRITE seal.
To support the usecase, this patch adds a new F_SEAL_FUTURE_WRITE seal
which prevents any future mmap and write syscalls from succeeding while
keeping the existing mmap active. The following program shows the seal
working in action:
#include <stdio.h>
#include <errno.h>
#include <sys/mman.h>
#include <linux/memfd.h>
#include <linux/fcntl.h>
#include <asm/unistd.h>
#include <unistd.h>
#define F_SEAL_FUTURE_WRITE 0x0010
#define REGION_SIZE (5 * 1024 * 1024)
int memfd_create_region(const char *name, size_t size)
{
int ret;
int fd = syscall(__NR_memfd_create, name, MFD_ALLOW_SEALING);
if (fd < 0) return fd;
ret = ftruncate(fd, size);
if (ret < 0) { close(fd); return ret; }
return fd;
}
int main() {
int ret, fd;
void *addr, *addr2, *addr3, *addr1;
ret = memfd_create_region("test_region", REGION_SIZE);
printf("ret=%d\n", ret);
fd = ret;
// Create map
addr = mmap(0, REGION_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
if (addr == MAP_FAILED)
printf("map 0 failed\n");
else
printf("map 0 passed\n");
if ((ret = write(fd, "test", 4)) != 4)
printf("write failed even though no future-write seal "
"(ret=%d errno =%d)\n", ret, errno);
else
printf("write passed\n");
addr1 = mmap(0, REGION_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
if (addr1 == MAP_FAILED)
perror("map 1 prot-write failed even though no seal\n");
else
printf("map 1 prot-write passed as expected\n");
ret = fcntl(fd, F_ADD_SEALS, F_SEAL_FUTURE_WRITE |
F_SEAL_GROW |
F_SEAL_SHRINK);
if (ret == -1)
printf("fcntl failed, errno: %d\n", errno);
else
printf("future-write seal now active\n");
if ((ret = write(fd, "test", 4)) != 4)
printf("write failed as expected due to future-write seal\n");
else
printf("write passed (unexpected)\n");
addr2 = mmap(0, REGION_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
if (addr2 == MAP_FAILED)
perror("map 2 prot-write failed as expected due to seal\n");
else
printf("map 2 passed\n");
addr3 = mmap(0, REGION_SIZE, PROT_READ, MAP_SHARED, fd, 0);
if (addr3 == MAP_FAILED)
perror("map 3 failed\n");
else
printf("map 3 prot-read passed as expected\n");
}
The output of running this program is as follows:
ret=3
map 0 passed
write passed
map 1 prot-write passed as expected
future-write seal now active
write failed as expected due to future-write seal
map 2 prot-write failed as expected due to seal
: Permission denied
map 3 prot-read passed as expected
[joel@joelfernandes.org: make F_SEAL_FUTURE_WRITE seal more robust]
Link: http://lkml.kernel.org/r/20181120052137.74317-1-joel@joelfernandes.org
Link: http://lkml.kernel.org/r/20181108041537.39694-1-joel@joelfernandes.org
Signed-off-by: Joel Fernandes (Google) <redacted>
Cc: John Stultz <redacted>
Cc: John Reck <redacted>
Cc: Todd Kjos <redacted>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Daniel Colascione <redacted>
Cc: J. Bruce Fields <redacted>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Khalid Aziz <redacted>
Cc: Lei Yang <redacted>
Cc: Marc-Andr Lureau <redacted>
Cc: Mike Kravetz <redacted>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Valdis Kletnieks <redacted>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
+ * write" seal active.
+ */
+ if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE) &&
+ (info->seals & F_SEAL_FUTURE_WRITE))
+ return -EPERM;
+
+ /*
+ * Since the F_SEAL_FUTURE_WRITE seals allow for a MAP_SHARED read-only
+ * mapping, take care to not allow mprotect to revert protections.
+ */
+ if (info->seals & F_SEAL_FUTURE_WRITE)
+ vma->vm_flags &= ~(VM_MAYWRITE);
+
This might all be clearer as:
if (info->seals & F_SEAL_FUTURE_WRITE) {
if (vma->vm_flags ...)
return -EPERM;
vma->vm_flags &= ~VM_MAYWRITE;
}
with appropriate comments inserted.
From: Joel Fernandes <hidden> Date: 2018-11-22 23:09:12
On Wed, Nov 21, 2018 at 07:25:26PM -0800, Andy Lutomirski wrote:
On Wed, Nov 21, 2018 at 6:27 PM Andrew Morton [off-list ref] wrote:
quoted
On Tue, 20 Nov 2018 13:13:35 -0800 Joel Fernandes [off-list ref] wrote:
quoted
quoted
quoted
I am Ok with whatever Andrew wants to do, if it is better to squash it with
the original, then I can do that and send another patch.
From experience, Andrew will food in fixups on request :)
Andrew, could you squash this patch into the one titled ("mm: Add an
F_SEAL_FUTURE_WRITE seal to memfd")?
Sure.
I could of course queue them separately but I rarely do so - I don't
think that the intermediate development states are useful in the
infinite-term, and I make them available via additional Link: tags in
the changelog footers anyway.
I think that the magnitude of these patches is such that John Stultz's
Reviewed-by is invalidated, so this series is now in the "unreviewed"
state.
So can we have a re-review please? For convenience, here's the
folded-together [1/1] patch, as it will go to Linus.
Sure, I removed the old tags and also provide an updated patch below inline.
quoted
From: "Joel Fernandes (Google)" <redacted>
Subject: mm: Add an F_SEAL_FUTURE_WRITE seal to memfd
Android uses ashmem for sharing memory regions. We are looking forward to
migrating all usecases of ashmem to memfd so that we can possibly remove
the ashmem driver in the future from staging while also benefiting from
using memfd and contributing to it. Note staging drivers are also not ABI
and generally can be removed at anytime.
+ * write" seal active.
+ */
+ if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_WRITE) &&
+ (info->seals & F_SEAL_FUTURE_WRITE))
+ return -EPERM;
+
+ /*
+ * Since the F_SEAL_FUTURE_WRITE seals allow for a MAP_SHARED read-only
+ * mapping, take care to not allow mprotect to revert protections.
+ */
+ if (info->seals & F_SEAL_FUTURE_WRITE)
+ vma->vm_flags &= ~(VM_MAYWRITE);
+
This might all be clearer as:
if (info->seals & F_SEAL_FUTURE_WRITE) {
if (vma->vm_flags ...)
return -EPERM;
vma->vm_flags &= ~VM_MAYWRITE;
}
with appropriate comments inserted.
Agreed, its simpler. Updated patch is below. I squashed it with all the
earlier ones. Andy, could you provide Acks and/or Reviewed-by tag as well?
---8<-----------------------
From b5a4960e755af67e9f6f9e65db5113e712cf338e Mon Sep 17 00:00:00 2001
From: "Joel Fernandes (Google)" <redacted>
Date: Sat, 10 Nov 2018 22:21:31 -0800
Subject: [PATCH v4] mm/memfd: Add an F_SEAL_FUTURE_WRITE seal to memfd
Android uses ashmem for sharing memory regions. We are looking forward to
migrating all usecases of ashmem to memfd so that we can possibly remove
the ashmem driver in the future from staging while also benefiting from
using memfd and contributing to it. Note staging drivers are also not ABI
and generally can be removed at anytime.
One of the main usecases Android has is the ability to create a region and
mmap it as writeable, then add protection against making any "future"
writes while keeping the existing already mmap'ed writeable-region active.
This allows us to implement a usecase where receivers of the shared
memory buffer can get a read-only view, while the sender continues to
write to the buffer. See CursorWindow documentation in Android for more
details:
https://developer.android.com/reference/android/database/CursorWindow
This usecase cannot be implemented with the existing F_SEAL_WRITE seal.
To support the usecase, this patch adds a new F_SEAL_FUTURE_WRITE seal
which prevents any future mmap and write syscalls from succeeding while
keeping the existing mmap active.
A better way to do F_SEAL_FUTURE_WRITE seal was discussed [1] last week
where we don't need to modify core VFS structures to get the same
behavior of the seal. This solves several side-effects pointed by Andy.
self-tests are provided in later patch to verify the expected semantics.
[1] https://lore.kernel.org/lkml/20181111173650.GA256781@google.com/
Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Joel Fernandes (Google) <redacted>
---
fs/hugetlbfs/inode.c | 2 +-
include/uapi/linux/fcntl.h | 1 +
mm/memfd.c | 3 ++-
mm/shmem.c | 26 +++++++++++++++++++++++---
4 files changed, 27 insertions(+), 5 deletions(-)
From: Joel Fernandes <hidden> Date: 2018-11-22 23:21:58
On Mon, Nov 19, 2018 at 09:21:37PM -0800, Joel Fernandes (Google) wrote:
Modify the tests for F_SEAL_FUTURE_WRITE based on the changes
introduced in previous patch.
Also add a test to make sure the reopen issue pointed by Jann Horn [1]
is fixed.
[1] https://lore.kernel.org/lkml/CAG48ez1h=v-JYnDw81HaYJzOfrNhwYksxmc2r=cJvdQVgYM+NA@mail.gmail.com/
Cc: Jann Horn <jannh@google.com>
Signed-off-by: Joel Fernandes (Google) <redacted>
---
tools/testing/selftests/memfd/memfd_test.c | 88 +++++++++++-----------
1 file changed, 44 insertions(+), 44 deletions(-)
Since we squashed [1] the mm/memfd patch modifications suggested by Andy into
the original patch, I also squashed the selftests modifications and appended
the patch inline below if you want to take this instead:
[1] https://lore.kernel.org/lkml/20181122230906.GA198127@google.com/T/#m8ba68f67f3ec24913a977b62bcaeafc4b194b8c8
---8<-----------------------
From: "Joel Fernandes (Google)" <redacted>
Subject: [PATCH v4] selftests/memfd: add tests for F_SEAL_FUTURE_WRITE seal
Add tests to verify sealing memfds with the F_SEAL_FUTURE_WRITE works as
expected.
Signed-off-by: Joel Fernandes (Google) <redacted>
---
tools/testing/selftests/memfd/memfd_test.c | 74 ++++++++++++++++++++++
1 file changed, 74 insertions(+)
@@ -54,6 +54,22 @@ static int mfd_assert_new(const char *name, loff_t sz, unsigned int flags)returnfd;}+staticintmfd_assert_reopen_fd(intfd_in)+{+intr,fd;+charpath[100];++sprintf(path,"/proc/self/fd/%d",fd_in);++fd=open(path,O_RDWR);+if(fd<0){+printf("re-open of existing fd %d failed\n",fd_in);+abort();+}++returnfd;+}+staticvoidmfd_fail_new(constchar*name,unsignedintflags){intr;
@@ -255,6 +271,25 @@ static void mfd_assert_read(int fd)munmap(p,mfd_def_size);}+/* Test that PROT_READ + MAP_SHARED mappings work. */+staticvoidmfd_assert_read_shared(intfd)+{+void*p;++/* verify PROT_READ and MAP_SHARED *is* allowed */+p=mmap(NULL,+mfd_def_size,+PROT_READ,+MAP_SHARED,+fd,+0);+if(p==MAP_FAILED){+printf("mmap() failed: %m\n");+abort();+}+munmap(p,mfd_def_size);+}+staticvoidmfd_assert_write(intfd){ssize_tl;
@@ -692,6 +727,44 @@ static void test_seal_write(void)close(fd);}+/*+*TestSEAL_FUTURE_WRITE+*TestwhetherSEAL_FUTURE_WRITEactuallypreventsmodifications.+*/+staticvoidtest_seal_future_write(void)+{+intfd,fd2;+void*p;++printf("%s SEAL-FUTURE-WRITE\n",memfd_str);++fd=mfd_assert_new("kern_memfd_seal_future_write",+mfd_def_size,+MFD_CLOEXEC|MFD_ALLOW_SEALING);++p=mfd_assert_mmap_shared(fd);++mfd_assert_has_seals(fd,0);++mfd_assert_add_seals(fd,F_SEAL_FUTURE_WRITE);+mfd_assert_has_seals(fd,F_SEAL_FUTURE_WRITE);++/* read should pass, writes should fail */+mfd_assert_read(fd);+mfd_assert_read_shared(fd);+mfd_fail_write(fd);++fd2=mfd_assert_reopen_fd(fd);+/* read should pass, writes should still fail */+mfd_assert_read(fd2);+mfd_assert_read_shared(fd2);+mfd_fail_write(fd2);++munmap(p,mfd_def_size);+close(fd2);+close(fd);+}+/**TestSEAL_SHRINK*TestwhetherSEAL_SHRINKactuallypreventsshrinking
@@ -945,6 +1018,7 @@ int main(int argc, char **argv)test_basic();test_seal_write();+test_seal_future_write();test_seal_shrink();test_seal_grow();test_seal_resize();
From: Andrew Morton <akpm@linux-foundation.org> Date: 2018-11-25 00:42:34
On Thu, 22 Nov 2018 15:09:06 -0800 Joel Fernandes [off-list ref] wrote:
Android uses ashmem for sharing memory regions. We are looking forward to
migrating all usecases of ashmem to memfd so that we can possibly remove
the ashmem driver in the future from staging while also benefiting from
using memfd and contributing to it. Note staging drivers are also not ABI
and generally can be removed at anytime.
One of the main usecases Android has is the ability to create a region and
mmap it as writeable, then add protection against making any "future"
writes while keeping the existing already mmap'ed writeable-region active.
This allows us to implement a usecase where receivers of the shared
memory buffer can get a read-only view, while the sender continues to
write to the buffer. See CursorWindow documentation in Android for more
details:
https://developer.android.com/reference/android/database/CursorWindow
This usecase cannot be implemented with the existing F_SEAL_WRITE seal.
To support the usecase, this patch adds a new F_SEAL_FUTURE_WRITE seal
which prevents any future mmap and write syscalls from succeeding while
keeping the existing mmap active.
A better way to do F_SEAL_FUTURE_WRITE seal was discussed [1] last week
where we don't need to modify core VFS structures to get the same
behavior of the seal. This solves several side-effects pointed by Andy.
self-tests are provided in later patch to verify the expected semantics.
[1] https://lore.kernel.org/lkml/20181111173650.GA256781@google.com/
This changelog doesn't have the nifty test case code which was in
earlier versions?
From: Joel Fernandes <hidden> Date: 2018-11-26 13:35:42
On Sat, Nov 24, 2018 at 04:47:36PM -0800, Matthew Wilcox wrote:
On Sat, Nov 24, 2018 at 04:42:29PM -0800, Andrew Morton wrote:
quoted
This changelog doesn't have the nifty test case code which was in
earlier versions?
Why do we put regression tests in the changelogs anyway? We have
tools/testing/selftests/vm/ already, perhaps they should go there?
The reason is I didn't add it was that test case went out of date and the
updated version of the test case went into the selftests in patch 2/2. I
thought that would suffice which covers all the cases. That's why I dropped
it. Would that be Ok?
The changelog of the previous series had it because the selftest was added
only later.
Let me know, thanks,
- Joel