Messages in this thread | | | Date | Fri, 27 Jan 2023 20:47:34 -0400 | From | Jason Gunthorpe <> | Subject | Re: [PATCH] iommufd: Add top-level bounds check on kernel buffer size |
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On Fri, Jan 27, 2023 at 02:38:17PM -0800, Kees Cook wrote: > While the op->size assignments are already bounds-checked at static > initializer time, these limits aren't aggregated and tracked when doing > later variable range checking under -Warray-bounds. Help the compiler > see that we know what we're talking about, and we'll never ask to > write more that sizeof(ucmd.cmd) bytes during the memset() inside > copy_struct_from_user(). Seen under GCC 13: > > In function 'copy_struct_from_user', > inlined from 'iommufd_fops_ioctl' at ../drivers/iommu/iommufd/main.c:333:8: > ../include/linux/fortify-string.h:59:33: warning: '__builtin_memset' offset [57, 4294967294] is out of the bounds [0, 56] of object 'buf' with type 'union ucmd_buffer' [-Warray-bounds=] > 59 | #define __underlying_memset __builtin_memset
This seems strange to me
I thought the way gcc handled this was if it knew the value must be in a certain range then it would check it
If it couldn't figure out any ranges it would not make a warning.
So why did it decide "rest" was in that really weird range?
Is this just a compiler bug?
Jason
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