Messages in this thread | | | Date | Fri, 9 Mar 2018 16:49:28 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH][RFC] rslib: Remove VLAs by setting upper bound on nroots |
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On Fri, 9 Mar 2018, Kees Cook wrote:
> Avoid VLAs[1] by always allocating the upper bound of stack space > needed. The existing users of rslib appear to max out at 32 roots, > so use that as the upper bound.
I think 32 is plenty. Do we have actually a user with 32?
> Alternative: make init_rs() a true caller-instance and pre-allocate > the workspaces. Will this need locking or are the callers already > single-threaded in their use of librs?
init_rs() is an init function which needs to be invoked _before_ the decoder/encoder can be used.
The way it works today that it can share the rs_control between users to avoid duplicating the polynom arrays and the setup of them.
So we might change how rs_control works and allocate rs_control for each invocation of init_rs(). That means we need two data structures:
Rename rs_control to rs_poly and just use that internaly for sharing the polynom arrays.
rs_control then becomes:
struct rs_control { struct rs_poly *poly; uint16_t lamda[MAX_ROOTS + 1]; .... uint16_t loc[MAX_ROOTS]; };
But as you said that requires serialization or separation at the usage sites.
drivers/mtd/nand/* would either need a mutex or allocate one rs_control per instance. Simple enough to do.
drivers/md/dm-verity-fec.c looks like it's allocating a dm control struct for each worker thread, so that should just require allocating one rs_control per worker then.
pstore only has an issue in case of OOPS. A simple solution would be to allocate two rs_control structs, one for regular usage and one for the OOPS case. Not sure if that covers all possible problems, so that needs more thoughts.
Thanks,
tglx
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