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fs_mgr: Add support for at-boot verification

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Running dm-verity on heavily accessed partitions leads to performance
slowdowns, especially on low-RAM and slow-CPU devices.

This patch introduces a flag to allow an entire verified partition to be
read once at boot, to check for corruptions. If the reads are
successful, we can mount the partition as raw & read-only, and if not,
we can revert to mounting it as a verity partition, just like before.

Usage of this flag will entail a slowdown of time-to-boot, but should
lead to improvements in runtime performance.

(cherry picked from commit 34543c03e6)

Bug: 32433608
Test: Compile
Change-Id: I97717683a00ad6fa347e63b72b1a9bf1d2946315
This commit is contained in:
Prashant Malani 2016-10-27 16:15:41 -07:00 committed by bowgotsai
parent 6ad690dfd4
commit 2cdc67eed5
1 changed files with 57 additions and 3 deletions
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60
fs_mgr/fs_mgr_verity.cpp
View file

@ -31,6 +31,7 @@
#include <android-base/file.h>
#include <android-base/strings.h>
#include <android-base/unique_fd.h>
#include <crypto_utils/android_pubkey.h>
#include <cutils/properties.h>
#include <logwrap/logwrap.h>
@ -73,6 +74,8 @@
#define VERITY_KMSG_RESTART "dm-verity device corrupted"
#define VERITY_KMSG_BUFSIZE 1024
#define READ_BUF_SIZE 4096
#define __STRINGIFY(x) #x
#define STRINGIFY(x) __STRINGIFY(x)
@ -205,6 +208,16 @@ static int create_verity_device(struct dm_ioctl *io, char *name, int fd)
return 0;
}
static int destroy_verity_device(struct dm_ioctl *io, char *name, int fd)
{
verity_ioctl_init(io, name, 0);
if (ioctl(fd, DM_DEV_REMOVE, io)) {
ERROR("Error removing device mapping (%s)", strerror(errno));
return -1;
}
return 0;
}
static int get_verity_device_name(struct dm_ioctl *io, char *name, int fd, char **dev_name)
{
verity_ioctl_init(io, name, 0);
@ -606,6 +619,30 @@ out:
return rc;
}
static int read_partition(const char *path, uint64_t size)
{
char buf[READ_BUF_SIZE];
ssize_t size_read;
android::base::unique_fd fd(TEMP_FAILURE_RETRY(open(path, O_RDONLY | O_CLOEXEC)));
if (fd == -1) {
ERROR("Failed to open %s: %s\n", path, strerror(errno));
return -errno;
}
while (size) {
size_read = TEMP_FAILURE_RETRY(read(fd, buf, READ_BUF_SIZE));
if (size_read == -1) {
ERROR("Error in reading partition %s: %s\n", path,
strerror(errno));
return -errno;
}
size -= size_read;
}
return 0;
}
static int compare_last_signature(struct fstab_rec *fstab, int *match)
{
char tag[METADATA_TAG_MAX_LENGTH + 1];
@ -904,6 +941,7 @@ int fs_mgr_setup_verity(struct fstab_rec *fstab, bool verify_dev)
alignas(dm_ioctl) char buffer[DM_BUF_SIZE];
struct dm_ioctl *io = (struct dm_ioctl *) buffer;
char *mount_point = basename(fstab->mount_point);
bool verified_at_boot = false;
if (fec_open(&f, fstab->blk_device, O_RDONLY, FEC_VERITY_DISABLE,
FEC_DEFAULT_ROOTS) < 0) {
@ -1037,10 +1075,26 @@ loaded:
// mark the underlying block device as read-only
fs_mgr_set_blk_ro(fstab->blk_device);
// Verify the entire partition in one go
// If there is an error, allow it to mount as a normal verity partition.
if (fstab->fs_mgr_flags & MF_VERIFYATBOOT) {
INFO("Verifying partition %s at boot\n", fstab->blk_device);
int err = read_partition(verity_blk_name, verity.data_size);
if (!err) {
INFO("Verified verity partition %s at boot\n", fstab->blk_device);
verified_at_boot = true;
}
}
// assign the new verity block device as the block device
free(fstab->blk_device);
fstab->blk_device = verity_blk_name;
verity_blk_name = 0;
if (!verified_at_boot) {
free(fstab->blk_device);
fstab->blk_device = verity_blk_name;
verity_blk_name = 0;
} else if (destroy_verity_device(io, mount_point, fd) < 0) {
ERROR("Failed to remove verity device %s\n", mount_point);
goto out;
}
// make sure we've set everything up properly
if (verify_dev && test_access(fstab->blk_device) < 0) {