linux/fs/ext4/ext4_crypto.h
Theodore Ts'o 3dbb5eb9a3 ext4 crypto: allocate bounce pages using GFP_NOWAIT
Previously we allocated bounce pages using a combination of
alloc_page() and mempool_alloc() with the __GFP_WAIT bit set.
Instead, use mempool_alloc() with GFP_NOWAIT.  The mempool_alloc()
function will try using alloc_pages() initially, and then only use the
mempool reserve of pages if alloc_pages() is unable to fulfill the
request.

This minimizes the the impact on the mm layer when we need to do a
large amount of writeback of encrypted files, as Jaeguk Kim had
reported that under a heavy fio workload on a system with restricted
amounts memory (which unfortunately, includes many mobile handsets),
he had observed the the OOM killer getting triggered several times.
Using GFP_NOWAIT

If the mempool_alloc() function fails, we will retry the page
writeback at a later time; the function of the mempool is to ensure
that we can writeback at least 32 pages at a time, so we can more
efficiently dispatch I/O under high memory pressure situations.  In
the future we should make this be a tunable so we can determine the
best tradeoff between permanently sequestering memory and the ability
to quickly launder pages so we can free up memory quickly when
necessary.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2015-06-03 09:32:39 -04:00

160 lines
4.0 KiB
C

/*
* linux/fs/ext4/ext4_crypto.h
*
* Copyright (C) 2015, Google, Inc.
*
* This contains encryption header content for ext4
*
* Written by Michael Halcrow, 2015.
*/
#ifndef _EXT4_CRYPTO_H
#define _EXT4_CRYPTO_H
#include <linux/fs.h>
#define EXT4_KEY_DESCRIPTOR_SIZE 8
/* Policy provided via an ioctl on the topmost directory */
struct ext4_encryption_policy {
char version;
char contents_encryption_mode;
char filenames_encryption_mode;
char flags;
char master_key_descriptor[EXT4_KEY_DESCRIPTOR_SIZE];
} __attribute__((__packed__));
#define EXT4_ENCRYPTION_CONTEXT_FORMAT_V1 1
#define EXT4_KEY_DERIVATION_NONCE_SIZE 16
#define EXT4_POLICY_FLAGS_PAD_4 0x00
#define EXT4_POLICY_FLAGS_PAD_8 0x01
#define EXT4_POLICY_FLAGS_PAD_16 0x02
#define EXT4_POLICY_FLAGS_PAD_32 0x03
#define EXT4_POLICY_FLAGS_PAD_MASK 0x03
#define EXT4_POLICY_FLAGS_VALID 0x03
/**
* Encryption context for inode
*
* Protector format:
* 1 byte: Protector format (1 = this version)
* 1 byte: File contents encryption mode
* 1 byte: File names encryption mode
* 1 byte: Reserved
* 8 bytes: Master Key descriptor
* 16 bytes: Encryption Key derivation nonce
*/
struct ext4_encryption_context {
char format;
char contents_encryption_mode;
char filenames_encryption_mode;
char flags;
char master_key_descriptor[EXT4_KEY_DESCRIPTOR_SIZE];
char nonce[EXT4_KEY_DERIVATION_NONCE_SIZE];
} __attribute__((__packed__));
/* Encryption parameters */
#define EXT4_XTS_TWEAK_SIZE 16
#define EXT4_AES_128_ECB_KEY_SIZE 16
#define EXT4_AES_256_GCM_KEY_SIZE 32
#define EXT4_AES_256_CBC_KEY_SIZE 32
#define EXT4_AES_256_CTS_KEY_SIZE 32
#define EXT4_AES_256_XTS_KEY_SIZE 64
#define EXT4_MAX_KEY_SIZE 64
#define EXT4_KEY_DESC_PREFIX "ext4:"
#define EXT4_KEY_DESC_PREFIX_SIZE 5
/* This is passed in from userspace into the kernel keyring */
struct ext4_encryption_key {
__u32 mode;
char raw[EXT4_MAX_KEY_SIZE];
__u32 size;
} __attribute__((__packed__));
struct ext4_crypt_info {
char ci_data_mode;
char ci_filename_mode;
char ci_flags;
struct crypto_ablkcipher *ci_ctfm;
struct key *ci_keyring_key;
char ci_master_key[EXT4_KEY_DESCRIPTOR_SIZE];
};
#define EXT4_CTX_REQUIRES_FREE_ENCRYPT_FL 0x00000001
#define EXT4_WRITE_PATH_FL 0x00000002
struct ext4_crypto_ctx {
union {
struct {
struct page *bounce_page; /* Ciphertext page */
struct page *control_page; /* Original page */
} w;
struct {
struct bio *bio;
struct work_struct work;
} r;
struct list_head free_list; /* Free list */
};
char flags; /* Flags */
char mode; /* Encryption mode for tfm */
};
struct ext4_completion_result {
struct completion completion;
int res;
};
#define DECLARE_EXT4_COMPLETION_RESULT(ecr) \
struct ext4_completion_result ecr = { \
COMPLETION_INITIALIZER((ecr).completion), 0 }
static inline int ext4_encryption_key_size(int mode)
{
switch (mode) {
case EXT4_ENCRYPTION_MODE_AES_256_XTS:
return EXT4_AES_256_XTS_KEY_SIZE;
case EXT4_ENCRYPTION_MODE_AES_256_GCM:
return EXT4_AES_256_GCM_KEY_SIZE;
case EXT4_ENCRYPTION_MODE_AES_256_CBC:
return EXT4_AES_256_CBC_KEY_SIZE;
case EXT4_ENCRYPTION_MODE_AES_256_CTS:
return EXT4_AES_256_CTS_KEY_SIZE;
default:
BUG();
}
return 0;
}
#define EXT4_FNAME_NUM_SCATTER_ENTRIES 4
#define EXT4_CRYPTO_BLOCK_SIZE 16
#define EXT4_FNAME_CRYPTO_DIGEST_SIZE 32
struct ext4_str {
unsigned char *name;
u32 len;
};
/**
* For encrypted symlinks, the ciphertext length is stored at the beginning
* of the string in little-endian format.
*/
struct ext4_encrypted_symlink_data {
__le16 len;
char encrypted_path[1];
} __attribute__((__packed__));
/**
* This function is used to calculate the disk space required to
* store a filename of length l in encrypted symlink format.
*/
static inline u32 encrypted_symlink_data_len(u32 l)
{
if (l < EXT4_CRYPTO_BLOCK_SIZE)
l = EXT4_CRYPTO_BLOCK_SIZE;
return (l + sizeof(struct ext4_encrypted_symlink_data) - 1);
}
#endif /* _EXT4_CRYPTO_H */