FAILED: patch "[PATCH] nbd: use shifts rather than multiplies" failed to apply to 5.4-stable tree
Subsystems (3)
[email protected]
maintainerThe patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 41e76c6a3c83c85e849f10754b8632ea763d9be4 Mon Sep 17 00:00:00 2001
From: Nick Desaulniers <[email protected]>
Date: Mon, 20 Sep 2021 16:25:33 -0700
Subject: [PATCH] nbd: use shifts rather than multiplies
commit fad7cd3310db ("nbd: add the check to prevent overflow in __nbd_ioctl()") raised an issue from the fallback helpers added in commit f0907827a8a9 ("compiler.h: enable builtin overflow checkers and add fallback code")
ERROR: modpost: "__divdi3" [drivers/block/nbd.ko] undefined!
As Stephen Rothwell notes:
The added check_mul_overflow() call is being passed 64 bit values. COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW is not set for this build (see include/linux/overflow.h).
Specifically, the helpers for checking whether the results of a multiplication overflowed (__unsigned_mul_overflow, __signed_add_overflow) use the division operator when !COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW. This is problematic for 64b operands on 32b hosts.
This was fixed upstream by
commit 76ae847497bc ("Documentation: raise minimum supported version of GCC to 5.1")
which is not suitable to be backported to stable.
Further, __builtin_mul_overflow() would emit a libcall to a compiler-rt-only symbol when compiling with clang < 14 for 32b targets.
ld.lld: error: undefined symbol: __mulodi4
In order to keep stable buildable with GCC 4.9 and clang < 14, modify struct nbd_config to instead track the number of bits of the block size; reconstructing the block size using runtime checked shifts that are not problematic for those compilers and in a ways that can be backported to stable.
In nbd_set_size, we do validate that the value of blksize must be a power of two (POT) and is in the range of [512, PAGE_SIZE] (both inclusive).
This does modify the debugfs interface.
drivers/block/nbd.c +17 -12
@@ -97,13 +97,18 @@ struct nbd_config {atomic_t recv_threads;wait_queue_head_t recv_wq; -loff_t blksize; +unsigned int blksize_bits;loff_t bytesize;#if IS_ENABLED (CONFIG_DEBUG_FS )struct dentry *dbg_dir;#endif }; +static inline unsigned int nbd_blksize (struct nbd_config *config) +{ +return 1u << config->blksize_bits; +} +struct nbd_device {struct blk_mq_tag_set tag_set;
@@ -146,7 +151,7 @@ static struct dentry *nbd_dbg_dir;#define NBD_MAGIC 0x68797548 -#define NBD_DEF_BLKSIZE 1024 +#define NBD_DEF_BLKSIZE_BITS 10static unsigned int nbds_max =16 ;static int max_part =16 ;
@@ -317,12 +322,12 @@ static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize, loff_t blksize) {if (!blksize) - blksize =NBD_DEF_BLKSIZE ; + blksize =1u <<NBD_DEF_BLKSIZE_BITS ;if (blksize <512 || blksize >PAGE_SIZE || !is_power_of_2 (blksize))return -EINVAL ; nbd->config->bytesize = bytesize; - nbd->config->blksize = blksize; + nbd->config->blksize_bits =__ffs (blksize);if (!nbd->task_recv)return 0 ;
@@ -1337,7 +1342,7 @@ static int nbd_start_device(struct nbd_device *nbd) args->index = i;queue_work (nbd->recv_workq, &args->work); } -return nbd_set_size (nbd, config->bytesize, config->blksize); +return nbd_set_size (nbd, config->bytesize,nbd_blksize (config)); }static int nbd_start_device_ioctl (struct nbd_device *nbd,struct block_device *bdev)
@@ -1406,11 +1411,11 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,case NBD_SET_BLKSIZE :return nbd_set_size (nbd, config->bytesize, arg);case NBD_SET_SIZE : -return nbd_set_size (nbd, arg, config->blksize); +return nbd_set_size (nbd, arg,nbd_blksize (config));case NBD_SET_SIZE_BLOCKS : -if (check_mul_overflow ((loff_t )arg, config->blksize, &bytesize)) +if (check_shl_overflow (arg, config->blksize_bits, &bytesize))return -EINVAL ; -return nbd_set_size (nbd, bytesize, config->blksize); +return nbd_set_size (nbd, bytesize,nbd_blksize (config));case NBD_SET_TIMEOUT :nbd_set_cmd_timeout (nbd, arg);return 0 ;
@@ -1476,7 +1481,7 @@ static struct nbd_config *nbd_alloc_config(void)atomic_set (&config->recv_threads,0 );init_waitqueue_head (&config->recv_wq);init_waitqueue_head (&config->conn_wait); - config->blksize =NBD_DEF_BLKSIZE ; + config->blksize_bits =NBD_DEF_BLKSIZE_BITS ;atomic_set (&config->live_connections,0 );try_module_get (THIS_MODULE );return config;
@@ -1604,7 +1609,7 @@ static int nbd_dev_dbg_init(struct nbd_device *nbd)debugfs_create_file ("tasks" ,0444 , dir, nbd, &nbd_dbg_tasks_fops);debugfs_create_u64 ("size_bytes" ,0444 , dir, &config->bytesize);debugfs_create_u32 ("timeout" ,0444 , dir, &nbd->tag_set.timeout); -debugfs_create_u64 ("blocksize" ,0444 , dir, &config->blksize); +debugfs_create_u32 ("blocksize_bits" ,0444 , dir, &config->blksize_bits);debugfs_create_file ("flags" ,0444 , dir, nbd, &nbd_dbg_flags_fops);return 0 ;
@@ -1826,7 +1831,7 @@ nbd_device_policy[NBD_DEVICE_ATTR_MAX + 1] = {static int nbd_genl_size_set (struct genl_info *info,struct nbd_device *nbd) {struct nbd_config *config = nbd->config; -u64 bsize = config->blksize; +u64 bsize =nbd_blksize (config);u64 bytes = config->bytesize;if (info->attrs[NBD_ATTR_SIZE_BYTES ])
@@ -1835,7 +1840,7 @@ static int nbd_genl_size_set(struct genl_info *info, struct nbd_device *nbd)if (info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES ]) bsize =nla_get_u64 (info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES ]); -if (bytes != config->bytesize || bsize != config->blksize) +if (bytes != config->bytesize || bsize !=nbd_blksize (config))return nbd_set_size (nbd, bytes, bsize);return 0 ; }