[PATCH v2] fs: semihosting: Fixup smh_flen and smh_read against overflow

Sean Anderson sean.anderson at seco.com
Thu Oct 2 17:42:32 CEST 2025


On 10/2/25 10:32, Andrew Goodbody wrote:
> The sys calls SYS_FLEN and SYS_READ were being used in a way that did
> not allow for file sizes > 2^31. Fixing this required changing the
> signatures of the functions smh_flen and smh_read to allow file
> sizes up to 2^32 - 2 and also being able to return errors that could be
> tested for.
> 
> This issue was found by Smatch.
> 
> Signed-off-by: Andrew Goodbody <andrew.goodbody at linaro.org>
> ---
> Changes in v2:
> - Fixup smh_flen and smh_read to allow for > 2^31 byte files
> - Link to v1: https://cas5-0-urlprotect.trendmicro.com:443/wis/clicktime/v1/query?url=https%3a%2f%2flore.kernel.org%2fr%2f20251002%2dfs%5fsemihosting%2dv1%2d1%2d1124e6becc51%40linaro.org&umid=ee8de4df-2479-48c7-83ae-b302789e6a41&rct=1759415558&auth=d807158c60b7d2502abde8a2fc01f40662980862-944860761829276b5cf613a133926bf7544353ff
> ---
>  common/spl/spl_semihosting.c        | 13 +++++++------
>  drivers/serial/serial_semihosting.c |  6 ++++--
>  fs/semihostingfs.c                  | 13 +++++++------
>  include/semihosting.h               | 13 +++++++------
>  lib/semihosting.c                   | 25 +++++++++++++++++++------
>  5 files changed, 44 insertions(+), 26 deletions(-)
> 
> diff --git a/common/spl/spl_semihosting.c b/common/spl/spl_semihosting.c
> index f36863fe48d25859ee9af67a67140893b6e9e262..fb578a274d0d937b2ed5bd13e505bcefd4491799 100644
> --- a/common/spl/spl_semihosting.c
> +++ b/common/spl/spl_semihosting.c
> @@ -13,13 +13,14 @@ static ulong smh_fit_read(struct spl_load_info *load, ulong file_offset,
>  			  ulong size, void *buf)
>  {
>  	long fd = *(long *)load->priv;
> -	ulong ret;
> +	long ret;
> +	size_t bytes_read;
>  
>  	if (smh_seek(fd, file_offset))
>  		return 0;
>  
> -	ret = smh_read(fd, buf, size);
> -	return ret < 0 ? 0 : ret;
> +	ret = smh_read(fd, buf, size, &bytes_read);
> +	return ret < 0 ? 0 : bytes_read;
>  }
>  
>  static int spl_smh_load_image(struct spl_image_info *spl_image,
> @@ -27,7 +28,8 @@ static int spl_smh_load_image(struct spl_image_info *spl_image,
>  {
>  	const char *filename = CONFIG_SPL_FS_LOAD_PAYLOAD_NAME;
>  	int ret;
> -	long fd, len;
> +	long fd;
> +	size_t len;
>  	struct spl_load_info load;
>  
>  	fd = smh_open(filename, MODE_READ | MODE_BINARY);
> @@ -36,12 +38,11 @@ static int spl_smh_load_image(struct spl_image_info *spl_image,
>  		return fd;
>  	}
>  
> -	ret = smh_flen(fd);
> +	ret = smh_flen(fd, &len);
>  	if (ret < 0) {
>  		log_debug("could not get length of image: %d\n", ret);
>  		goto out;
>  	}
> -	len = ret;
>  
>  	spl_load_init(&load, smh_fit_read, &fd, 1);
>  	ret = spl_load(spl_image, bootdev, &load, len, 0);
> diff --git a/drivers/serial/serial_semihosting.c b/drivers/serial/serial_semihosting.c
> index 56a5ec72428afdd97eccad739a46189380ba3e76..017b1f8eda84f5c25e09be7e970d0ebfdbf2ace0 100644
> --- a/drivers/serial/serial_semihosting.c
> +++ b/drivers/serial/serial_semihosting.c
> @@ -25,11 +25,12 @@ static int smh_serial_getc(struct udevice *dev)
>  {
>  	char ch = 0;
>  	struct smh_serial_priv *priv = dev_get_priv(dev);
> +	size_t bytes_read;
>  
>  	if (priv->infd < 0)
>  		return smh_getc();
>  
> -	smh_read(priv->infd, &ch, sizeof(ch));
> +	smh_read(priv->infd, &ch, sizeof(ch), &bytes_read);
>  	return ch;
>  }
>  
> @@ -140,11 +141,12 @@ static void smh_serial_setbrg(void)
>  static int smh_serial_getc(void)
>  {
>  	char ch = 0;
> +	size_t bytes_read;
>  
>  	if (infd < 0)
>  		return smh_getc();
>  
> -	smh_read(infd, &ch, sizeof(ch));
> +	smh_read(infd, &ch, sizeof(ch), &bytes_read);
>  	return ch;
>  }
>  
> diff --git a/fs/semihostingfs.c b/fs/semihostingfs.c
> index 77e39ca407e4d240a1fd573497c5b6b908816454..71b6634b0660e32cc63f7fc60ec1af8d3248433a 100644
> --- a/fs/semihostingfs.c
> +++ b/fs/semihostingfs.c
> @@ -23,7 +23,8 @@ int smh_fs_set_blk_dev(struct blk_desc *rbdd, struct disk_partition *info)
>  static int smh_fs_read_at(const char *filename, loff_t pos, void *buffer,
>  			  loff_t maxsize, loff_t *actread)
>  {
> -	long fd, size, ret;
> +	long fd, ret;
> +	size_t size;
>  
>  	fd = smh_open(filename, MODE_READ | MODE_BINARY);
>  	if (fd < 0)
> @@ -34,19 +35,19 @@ static int smh_fs_read_at(const char *filename, loff_t pos, void *buffer,
>  		return ret;
>  	}
>  	if (!maxsize) {
> -		size = smh_flen(fd);
> +		ret = smh_flen(fd, &size);
>  		if (ret < 0) {
>  			smh_close(fd);
> -			return size;
> +			return ret;
>  		}
>  
>  		maxsize = size;
>  	}
>  
> -	size = smh_read(fd, buffer, maxsize);
> +	ret = smh_read(fd, buffer, maxsize, &size);
>  	smh_close(fd);
> -	if (size < 0)
> -		return size;
> +	if (ret < 0)
> +		return ret;
>  
>  	*actread = size;
>  	return 0;
> diff --git a/include/semihosting.h b/include/semihosting.h
> index 4e844cbad87bb1ae6bb365f87f3e7a8aeea445f4..60535199b9532ce16620aea3ca1ea741c5b73766 100644
> --- a/include/semihosting.h
> +++ b/include/semihosting.h
> @@ -95,12 +95,12 @@ long smh_open(const char *fname, enum smh_open_mode mode);
>   * @fd: A file descriptor returned from smh_open()
>   * @memp: Pointer to a buffer of memory of at least @len bytes
>   * @len: The number of bytes to read
> + * @read_len: Pointer which will be updated with actual bytes read on success,
> + *  with 0 indicating %EOF
>   *
> - * Return:
> - * * The number of bytes read on success, with 0 indicating %EOF
> - * * A negative error on failure
> + * Return: 0 on success or negative error on failure
>   */
> -long smh_read(long fd, void *memp, size_t len);
> +long smh_read(long fd, void *memp, size_t len, size_t *read_len);
>  
>  /**
>   * smh_write() - Write data to a file
> @@ -124,10 +124,11 @@ long smh_close(long fd);
>  /**
>   * smh_flen() - Get the length of a file
>   * @fd: A file descriptor returned from smh_open()
> + * @size: Pointer which will be updated with length of file on success
>   *
> - * Return: The length of the file, in bytes, or a negative error on failure
> + * Return: 0 on success or negative error on failure
>   */
> -long smh_flen(long fd);
> +int smh_flen(long fd, size_t *size);
>  
>  /**
>   * smh_seek() - Seek to a position in a file
> diff --git a/lib/semihosting.c b/lib/semihosting.c
> index 9be5bffd30124777c4f8110065e6cca5640312ac..a0f42d41e4a7ad95023c684f6824bfc677ad25cd 100644
> --- a/lib/semihosting.c
> +++ b/lib/semihosting.c
> @@ -93,9 +93,9 @@ struct smh_rdwr_s {
>  	size_t len;
>  };
>  
> -long smh_read(long fd, void *memp, size_t len)
> +long smh_read(long fd, void *memp, size_t len, size_t *read_len)
>  {
> -	long ret;
> +	size_t ret;
>  	struct smh_rdwr_s read;
>  
>  	debug("%s: fd %ld, memp %p, len %zu\n", __func__, fd, memp, len);
> @@ -105,9 +105,20 @@ long smh_read(long fd, void *memp, size_t len)
>  	read.len = len;
>  
>  	ret = smh_trap(SYSREAD, &read);
> -	if (ret < 0)
> +	if (!ret) {
> +		/* Success */
> +		*read_len = len;
> +		return 0;
> +	} else if (ret == len) {
> +		/* EOF */
> +		*read_len = 0;
> +		return 0;
> +	} else {
> +		/* Partial success */
> +		*read_len = len - ret;
>  		return smh_errno();
> -	return len - ret;
> +	}
> +
>  }
>  
>  long smh_write(long fd, const void *memp, size_t len, ulong *written)
> @@ -140,7 +151,7 @@ long smh_close(long fd)
>  	return 0;
>  }
>  
> -long smh_flen(long fd)
> +int smh_flen(long fd, size_t *size)
>  {
>  	long ret;
>  
> @@ -149,7 +160,9 @@ long smh_flen(long fd)
>  	ret = smh_trap(SYSFLEN, &fd);
>  	if (ret == -1)
>  		return smh_errno();
> -	return ret;
> +
> +	*size = (size_t)ret;
> +	return 0;

This is completely wrong. long is 32-bits on 32-bit systems, so you
cannot get the upper 64 bits just by casting to a size_t.

--Sean


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