[PATCH v2 0/4] Block layer patches for kernel v5.8

[PATCH v2 0/4] Block layer patches for kernel v5.8

[Bart Van Assche]

Hi Jens,

The patches in this series are what I came up with as the result of
analyzing Alexander Potapenko's report about reading from null_blk.
Please consider these patches for kernel v5.8.

Thanks,

Bart.

Changes compared to v1:
- Adjusted the comments added by patch "Document the bio_vec properties" as
  requested by Christoph.
- Left out the patch "Fix zero_fill_bio()" since it is not necessary.
- Moved zero_fill_bvec() from patch "Fix zero_fill_bio()" into patch
  "null_blk: Zero-initialize read buffers in non-memory-backed mode".

Bart Van Assche (4):
  block: Fix type of first compat_put_{,u}long() argument
  bio.h: Declare the arguments of the bio iteration functions const
  block: Document the bio_vec properties
  null_blk: Zero-initialize read buffers in non-memory-backed mode

 block/ioctl.c                 |  4 +--
 drivers/block/null_blk_main.c | 50 +++++++++++++++++++++++++++++++++++
 include/linux/bio.h           |  6 ++---
 include/linux/bvec.h          | 13 +++++++--
 4 files changed, 66 insertions(+), 7 deletions(-)

[PATCH v2 1/4] block: Fix type of first compat_put_{,u}long() argument

[Bart Van Assche]

This patch fixes the following sparse warnings:

block/ioctl.c:209:16: warning: incorrect type in argument 1 (different address spaces)
block/ioctl.c:209:16:    expected void const volatile [noderef] <asn:1> *
block/ioctl.c:209:16:    got signed int [usertype] *argp
block/ioctl.c:214:16: warning: incorrect type in argument 1 (different address spaces)
block/ioctl.c:214:16:    expected void const volatile [noderef] <asn:1> *
block/ioctl.c:214:16:    got unsigned int [usertype] *argp
block/ioctl.c:666:40: warning: incorrect type in argument 1 (different address spaces)
block/ioctl.c:666:40:    expected signed int [usertype] *argp
block/ioctl.c:666:40:    got void [noderef] <asn:1> *argp
block/ioctl.c:672:41: warning: incorrect type in argument 1 (different address spaces)
block/ioctl.c:672:41:    expected unsigned int [usertype] *argp
block/ioctl.c:672:41:    got void [noderef] <asn:1> *argp

Cc: Arnd Bergmann <arnd@arndb.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Fixes: 9b81648cb5e3 ("compat_ioctl: simplify up block/ioctl.c")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 block/ioctl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/block/ioctl.c b/block/ioctl.c
index 75c64811b534..bdb3bbb253d9 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -204,12 +204,12 @@ static int put_u64(u64 __user *argp, u64 val)
 }
 
 #ifdef CONFIG_COMPAT
-static int compat_put_long(compat_long_t *argp, long val)
+static int compat_put_long(compat_long_t __user *argp, long val)
 {
 	return put_user(val, argp);
 }
 
-static int compat_put_ulong(compat_ulong_t *argp, compat_ulong_t val)
+static int compat_put_ulong(compat_ulong_t __user *argp, compat_ulong_t val)
 {
 	return put_user(val, argp);
 }

[PATCH v2 2/4] bio.h: Declare the arguments of the bio iteration functions const

[Bart Van Assche]

This change makes it possible to pass 'const struct bio *' arguments to
these functions.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Damien Le Moal <damien.lemoal@wdc.com>
Cc: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Cc: Alexander Potapenko <glider@google.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 include/linux/bio.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/bio.h b/include/linux/bio.h
index a0ee494a6329..950c9dc44c4f 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -70,7 +70,7 @@ static inline bool bio_has_data(struct bio *bio)
 	return false;
 }
 
-static inline bool bio_no_advance_iter(struct bio *bio)
+static inline bool bio_no_advance_iter(const struct bio *bio)
 {
 	return bio_op(bio) == REQ_OP_DISCARD ||
 	       bio_op(bio) == REQ_OP_SECURE_ERASE ||
@@ -138,8 +138,8 @@ static inline bool bio_next_segment(const struct bio *bio,
 #define bio_for_each_segment_all(bvl, bio, iter) \
 	for (bvl = bvec_init_iter_all(&iter); bio_next_segment((bio), &iter); )
 
-static inline void bio_advance_iter(struct bio *bio, struct bvec_iter *iter,
-				    unsigned bytes)
+static inline void bio_advance_iter(const struct bio *bio,
+				    struct bvec_iter *iter, unsigned int bytes)
 {
 	iter->bi_sector += bytes >> 9;
 

[PATCH v2 3/4] block: Document the bio_vec properties

[Bart Van Assche]

Since it is nontrivial that nth_page() does not have to be used for a
bio_vec, document this.

CC: Christoph Hellwig <hch@infradead.org>
Cc: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 include/linux/bvec.h | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/include/linux/bvec.h b/include/linux/bvec.h
index a81c13ac1972..ac0c7299d5b8 100644
--- a/include/linux/bvec.h
+++ b/include/linux/bvec.h
@@ -12,8 +12,17 @@
 #include <linux/errno.h>
 #include <linux/mm.h>
 
-/*
- * was unsigned short, but we might as well be ready for > 64kB I/O pages
+/**
+ * struct bio_vec - a contiguous range of physical memory addresses
+ * @bv_page:   First page associated with the address range.
+ * @bv_len:    Number of bytes in the address range.
+ * @bv_offset: Start of the address range relative to the start of @bv_page.
+ *
+ * The following holds for a bvec if n * PAGE_SIZE < bv_offset + bv_len:
+ *
+ *   nth_page(@bv_page, n) == @bv_page + n
+ *
+ * This holds because page_is_mergeable() checks the above property.
  */
 struct bio_vec {
 	struct page	*bv_page;

[PATCH v2 4/4] null_blk: Zero-initialize read buffers in non-memory-backed mode

[Bart Van Assche]

This patch suppresses an uninteresting KMSAN complaint without affecting
performance of the null_blk driver if CONFIG_KMSAN is disabled.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Damien Le Moal <damien.lemoal@wdc.com>
Cc: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Cc: Alexander Potapenko <glider@google.com>
Reported-by: Alexander Potapenko <glider@google.com>
Tested-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/block/null_blk_main.c | 50 +++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/drivers/block/null_blk_main.c b/drivers/block/null_blk_main.c
index 06f5761fccb6..0c1df6ecb30b 100644
--- a/drivers/block/null_blk_main.c
+++ b/drivers/block/null_blk_main.c
@@ -1250,8 +1250,58 @@ static inline blk_status_t null_handle_memory_backed(struct nullb_cmd *cmd,
 	return errno_to_blk_status(err);
 }
 
+static void zero_fill_bvec(const struct bio_vec *bvec)
+{
+	struct page *page = bvec->bv_page;
+	u32 offset = bvec->bv_offset;
+	u32 left = bvec->bv_len;
+
+	while (left) {
+		u32 len = min_t(u32, left, PAGE_SIZE - offset);
+		void *kaddr;
+
+		kaddr = kmap_atomic(page);
+		memset(kaddr + offset, 0, len);
+		flush_dcache_page(page);
+		kunmap_atomic(kaddr);
+		page++;
+		left -= len;
+		offset = 0;
+	}
+}
+
+static void nullb_zero_rq_data_buffer(const struct request *rq)
+{
+	struct req_iterator iter;
+	struct bio_vec bvec;
+
+	rq_for_each_bvec(bvec, rq, iter)
+		zero_fill_bvec(&bvec);
+}
+
+static void nullb_zero_read_cmd_buffer(struct nullb_cmd *cmd)
+{
+	struct nullb_device *dev = cmd->nq->dev;
+
+	if (dev->queue_mode == NULL_Q_BIO && bio_op(cmd->bio) == REQ_OP_READ)
+		zero_fill_bio(cmd->bio);
+	else if (req_op(cmd->rq) == REQ_OP_READ)
+		nullb_zero_rq_data_buffer(cmd->rq);
+}
+
+/* Complete a request. Only called if dev->memory_backed == 0. */
 static inline void nullb_complete_cmd(struct nullb_cmd *cmd)
 {
+	/*
+	 * Since root privileges are required to configure the null_blk
+	 * driver, it is fine that this driver does not initialize the
+	 * data buffers of read commands. Zero-initialize these buffers
+	 * anyway if KMSAN is enabled to prevent that KMSAN complains
+	 * about null_blk not initializing read data buffers.
+	 */
+	if (IS_ENABLED(CONFIG_KMSAN))
+		nullb_zero_read_cmd_buffer(cmd);
+
 	/* Complete IO by inline, softirq or timer */
 	switch (cmd->nq->dev->irqmode) {
 	case NULL_IRQ_SOFTIRQ:

Re: [PATCH v2 4/4] null_blk: Zero-initialize read buffers in non-memory-backed mode

[Ming Lei]

On Sun, May 17, 2020 at 06:48:07PM -0700, Bart Van Assche wrote:
> This patch suppresses an uninteresting KMSAN complaint without affecting
> performance of the null_blk driver if CONFIG_KMSAN is disabled.
> 
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Ming Lei <ming.lei@redhat.com>
> Cc: Damien Le Moal <damien.lemoal@wdc.com>
> Cc: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
> Cc: Alexander Potapenko <glider@google.com>
> Reported-by: Alexander Potapenko <glider@google.com>
> Tested-by: Alexander Potapenko <glider@google.com>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>  drivers/block/null_blk_main.c | 50 +++++++++++++++++++++++++++++++++++
>  1 file changed, 50 insertions(+)
> 
> diff --git a/drivers/block/null_blk_main.c b/drivers/block/null_blk_main.c
> index 06f5761fccb6..0c1df6ecb30b 100644
> --- a/drivers/block/null_blk_main.c
> +++ b/drivers/block/null_blk_main.c
> @@ -1250,8 +1250,58 @@ static inline blk_status_t null_handle_memory_backed(struct nullb_cmd *cmd,
>  	return errno_to_blk_status(err);
>  }
>  
> +static void zero_fill_bvec(const struct bio_vec *bvec)
> +{
> +	struct page *page = bvec->bv_page;
> +	u32 offset = bvec->bv_offset;
> +	u32 left = bvec->bv_len;
> +
> +	while (left) {
> +		u32 len = min_t(u32, left, PAGE_SIZE - offset);
> +		void *kaddr;
> +
> +		kaddr = kmap_atomic(page);
> +		memset(kaddr + offset, 0, len);
> +		flush_dcache_page(page);
> +		kunmap_atomic(kaddr);
> +		page++;
> +		left -= len;
> +		offset = 0;
> +	}
> +}
> +
> +static void nullb_zero_rq_data_buffer(const struct request *rq)
> +{
> +	struct req_iterator iter;
> +	struct bio_vec bvec;
> +
> +	rq_for_each_bvec(bvec, rq, iter)
> +		zero_fill_bvec(&bvec);
> +}

Not necessary to add zero_fill_bvec(), and it can be done in the
following two line code:

	__rq_for_each_bio(bio, rq)
		zero_fill_bio(bio);


Thanks,
Ming

Re: [PATCH v2 3/4] block: Document the bio_vec properties

[Christoph Hellwig]

On Sun, May 17, 2020 at 06:48:06PM -0700, Bart Van Assche wrote:
> Since it is nontrivial that nth_page() does not have to be used for a
> bio_vec, document this.

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>