Re: [PATCH v2 13/19] udf: prevent bounds-check bypass via speculative execution

[Jan Kara]

On Thu 11-01-18 16:47:35, Dan Williams wrote:
> Static analysis reports that 'eahd->appAttrLocation' and
> 'eahd->impAttrLocation' may be a user controlled values that are used as
> data dependencies for calculating source and destination buffers for
> memmove operations. In order to avoid potential leaks of kernel memory
> values, block speculative execution of the instruction stream that could
> issue further reads based on invalid 'aal' or 'ial' values.
> 
> Based on an original patch by Elena Reshetova.
> 
> Cc: Jan Kara <jack@xxxxxxxx>
> Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>

Dan, I've already emailed to you [1] why I don't think this patch is needed
at all. Do you disagree or did my email just get lost?

[1] https://marc.info/?l=linux-arch&m=151540683024125&w=2

								Honza

> ---
>  fs/udf/misc.c |   40 ++++++++++++++++++++++------------------
>  1 file changed, 22 insertions(+), 18 deletions(-)
> 
> diff --git a/fs/udf/misc.c b/fs/udf/misc.c
> index 401e64cde1be..693e24699928 100644
> --- a/fs/udf/misc.c
> +++ b/fs/udf/misc.c
> @@ -22,6 +22,7 @@
>  #include "udfdecl.h"
>  
>  #include <linux/fs.h>
> +#include <linux/nospec.h>
>  #include <linux/string.h>
>  #include <linux/crc-itu-t.h>
>  
> @@ -51,6 +52,8 @@ struct genericFormat *udf_add_extendedattr(struct inode *inode, uint32_t size,
>  	int offset;
>  	uint16_t crclen;
>  	struct udf_inode_info *iinfo = UDF_I(inode);
> +	uint8_t *ea_dst, *ea_src;
> +	uint32_t aal, ial;
>  
>  	ea = iinfo->i_ext.i_data;
>  	if (iinfo->i_lenEAttr) {
> @@ -100,33 +103,34 @@ struct genericFormat *udf_add_extendedattr(struct inode *inode, uint32_t size,
>  
>  		offset = iinfo->i_lenEAttr;
>  		if (type < 2048) {
> -			if (le32_to_cpu(eahd->appAttrLocation) <
> -					iinfo->i_lenEAttr) {
> -				uint32_t aal =
> -					le32_to_cpu(eahd->appAttrLocation);
> -				memmove(&ea[offset - aal + size],
> -					&ea[aal], offset - aal);
> +			aal = le32_to_cpu(eahd->appAttrLocation);
> +			ea_dst = array_ptr(ea, offset - aal + size,
> +					iinfo->i_lenEAttr);
> +			ea_src = array_ptr(ea, aal, iinfo->i_lenEAttr);
> +			if (ea_dst && ea_src) {
> +				memmove(ea_dst, ea_src, offset - aal);
>  				offset -= aal;
>  				eahd->appAttrLocation =
>  						cpu_to_le32(aal + size);
>  			}
> -			if (le32_to_cpu(eahd->impAttrLocation) <
> -					iinfo->i_lenEAttr) {
> -				uint32_t ial =
> -					le32_to_cpu(eahd->impAttrLocation);
> -				memmove(&ea[offset - ial + size],
> -					&ea[ial], offset - ial);
> +
> +			ial = le32_to_cpu(eahd->impAttrLocation);
> +			ea_dst = array_ptr(ea, offset - ial + size,
> +					iinfo->i_lenEAttr);
> +			ea_src = array_ptr(ea, ial, iinfo->i_lenEAttr);
> +			if (ea_dst && ea_src) {
> +				memmove(ea_dst, ea_src, offset - ial);
>  				offset -= ial;
>  				eahd->impAttrLocation =
>  						cpu_to_le32(ial + size);
>  			}
>  		} else if (type < 65536) {
> -			if (le32_to_cpu(eahd->appAttrLocation) <
> -					iinfo->i_lenEAttr) {
> -				uint32_t aal =
> -					le32_to_cpu(eahd->appAttrLocation);
> -				memmove(&ea[offset - aal + size],
> -					&ea[aal], offset - aal);
> +			aal = le32_to_cpu(eahd->appAttrLocation);
> +			ea_dst = array_ptr(ea, offset - aal + size,
> +					iinfo->i_lenEAttr);
> +			ea_src = array_ptr(ea, aal, iinfo->i_lenEAttr);
> +			if (ea_dst && ea_src) {
> +				memmove(ea_dst, ea_src, offset - aal);
>  				offset -= aal;
>  				eahd->appAttrLocation =
>  						cpu_to_le32(aal + size);
> 
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR